- a study that helps determine the content of incomplete anti-erythrocyte antibodies in the blood. This antiglobulin test allows you to detect antibodies to in pregnant women.
In addition, it makes it possible to diagnose hemolytic anemia in newborns with Rh conflict at the initial stages. This helps prevent the destruction of red blood cells necessary for normal blood formation. This test was created in 1945 by Robert Coombs, which is why it got its name.
The Coombs test is a versatile test that allows for timely diagnosis of hematopoietic disorders in both adults and children.
There are the following types of such tests:
- Direct Coombs test– allows you to determine antibodies located on the surface of red blood cells. Typically, such a study is prescribed for suspected hemolysis, autoimmune hemolytic anemia, or other autoimmune diseases. In addition, it is carried out after drug therapy drugs based on quinine, penicillin or methyldopa, or after a blood transfusion. To obtain more accurate results, you must completely stop taking medications for at least 1 week before the study.
- Indirect Coombs test– a test that can be used to detect anti-erythrocyte antibodies in plasma. It is usually performed during pregnancy and before a blood transfusion. Anti-erythrocyte antibodies appear in a person’s blood during a reactive immune system or as a reaction to certain medications. For a more accurate study, several samplings are carried out at once with an interval of 2 hours.
Indications for use
The Coombs test is performed only if there are serious indications. This is an expensive and time-consuming study, which is a specific test.
Typically, the following situations are considered indications for its implementation:
- During blood transfusion. The test allows you to determine whether the recipient's blood will take root in the human body, as well as whether donation is possible. In this case, it is necessary to examine the material from both the donor and the recipient. It is important to determine the nature of the antibodies, because if they are incompatible in the body against the background of Rh conflict, the immune system is destroyed. This leads to the development serious illnesses, and in rare cases even death.
- Before surgery when there is a risk of blood loss. This is done so that the doctor can immediately introduce suitable blood to restore the body.
- To detect Rh sensitization. Rhesus is a specific antigen that appears in the body of every woman during pregnancy. If the mother has positive Rh and the father negative, or vice versa, there is no dependence for the child - he can inherit anyone. If the child receives the opposite rhesus from the mother, there is a high risk of sensitization. This phenomenon is characterized by the mixing of the blood of mother and child. This can happen both during gestation and during birth.
If a Rhesus conflict occurs in the body of a pregnant woman, then the mother’s immune system begins to perceive her fetus as foreign body. Because of this, there is a high risk that he will begin to attack him.
As a result of such actions, the baby may develop serious pathologies. Most often, erythroblastosis occurs - a phenomenon in which the child’s body cannot produce enough red blood cells.
In addition, due to Rh conflict, fetal death may occur in the womb or immediately after birth. At the right approach Such serious consequences can be easily avoided by treatment.
Deviations from the norm
If the Coombs test is positive, the doctor concludes that there are antibodies to red blood cells in the blood serum. This means that the donor's blood may not be compatible with the patient's blood.
If a positive result is diagnosed in the body of a pregnant woman with Rh-negative blood, then her body contains antibodies to the blood of the fetus.
This indicates a Rh conflict, which requires an extremely careful approach to pregnancy management on the part of the doctor, as well as compliance with all instructions and recommendations from the woman.
If antibodies are present in the child’s blood, it is diagnosed hemolytic disease newborns. In this case, a repeat study is carried out to determine whether the increase in antibody levels in the blood of the expectant mother occurs or not.
Possible complications from the Coombs test
The Coombs test is a fairly safe test that makes it possible to diagnose a number of autoimmune diseases. It rarely causes complications, usually negative consequences associated with blood sampling.
They are:
- Bleeding or hemorrhages under the skin
- Dizziness and fainting
- Infectious infection
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– an antiglobulin test aimed at identifying in Rh-negative blood incomplete anti-erythrocyte antibodies to the Rh factor - a specific protein that is located on the surface of the erythrocytes of Rh-positive blood. There are two types of this test: direct - detection of antibodies on the surface of red blood cells, indirect - detection of antibodies in blood serum. Direct testing is carried out in the diagnosis and monitoring of treatment of blood diseases: hemolytic anemia, hemolytic disease of newborns and others. An indirect test is performed to assess the compatibility of the blood of the donor and recipient during transfusion, as well as to determine the presence and risk of Rh conflict when planning and managing pregnancy. The material for the Coombs test is venous blood; the study is carried out using methods based on the agglutination reaction. Normally, both tests give a negative result. The analysis is completed within one day.
Coombs test – clinical trial Rh-negative blood, aimed at detecting antibodies to the Rh factor. The test is used to identify the risk of developing Rh conflict and hemolytic reactions. In each person, the surface of red blood cells contains a certain set of antigens or agglutinogens - compounds of various natures, the presence or absence of which is used to determine the blood type and Rh factor. There are many types of antigens, including medical practice Agglutinogens A and B, which determine the blood group, and agglutinogen D, the Rh factor, are of greatest practical importance. With a positive Rh factor, D antigens are detected on the outer membrane of erythrocytes, but with a negative factor, they are not.
The Coombs test, also called the antiglobulin test, is aimed at detecting incomplete anti-erythrocyte antibodies to the Rh factor system in the blood. Antibodies to the Rh factor are specific immunoglobulins that are produced in Rh-negative blood when red blood cells with agglutinogens D enter it. This can happen when the blood of a fetus and a pregnant woman is mixed, during blood transfusions carried out without prior blood typing. The Coombs test exists in two versions - direct and indirect. When performing a direct Coombs test, antibodies attached to the surface of red blood cells are detected. The study is used to determine the cause of the hemolytic reaction. The indirect Coombs test is aimed at detecting anti-erythrocyte antibodies in blood plasma. It is necessary to determine the compatibility of blood between donor and recipient or mother and fetus, and helps prevent the development of Rh conflict and subsequent hemolysis of red blood cells.
Blood for both versions of the Coombs test is taken from a vein. The analysis is performed by agglutination using antiglobulin serum. The results of the study are used in hematology to identify the causes of hemolytic reactions, in surgery and resuscitation when conducting blood transfusions, in obstetrics and gynecology when monitoring pregnancies in women with Rh-negative blood.
Indications
The direct Coombs test, which detects antibodies attached to the surface of red blood cells, is prescribed for hemolytic reactions (destruction of red blood cells) of various origins. The study is indicated for primary autoimmune hemolytic anemia, post-transfusion hemolytic anemia, hemolytic disease of the newborn, hemolysis of erythrocytes caused by autoimmune, tumor or infectious diseases, as well as reception medicines, for example, quinidine, methyldopa, procainamide. The indirect Coombs test, which determines antibodies in blood plasma, is used to prevent the development of Rh conflict. It is indicated for patients in preparation for blood transfusions, as well as for pregnant women with a negative Rh factor, provided that the future father of the child has a positive Rh factor.
To determine Rh compatibility, the Coombs test is not prescribed to patients with Rh-positive blood. In these cases, there are already antigens on the surface of red blood cells; the production of antibodies cannot be provoked by blood transfusion or the entry of fetal blood into the bloodstream of the pregnant woman. Also, the study is not indicated for pregnant women if both parents have a negative Rh factor - an inherited recessive trait. The child in such couples always has Rh-negative blood; an immunological conflict with the mother is impossible. In hemolytic pathologies, the antiglobulin test is not used to monitor the success of therapy, since the results do not reflect the activity of the process of destruction of red blood cells.
A limitation of the Coombs test is the laboriousness of the research procedure - to obtain reliable results, it is necessary to comply with temperature and time conditions, rules for the preparation of reagents and biomaterial. The advantages of the Coombs test include its high sensitivity. In hemolytic anemia, the results of this test remain positive, even if the hemoglobin, bilirubin and reticulocyte levels are normalized.
Preparation for analysis and collection of material
The material used to perform the Coombs test is venous blood. There are no special requirements for the time of the blood sampling procedure and for the preparation of the patient. As with any study, it is recommended to take a break after eating for at least 4 hours, and stop smoking in the last 30 minutes. physical activity, avoid emotional stress. It is also worth discussing with your doctor in advance the need to stop taking medications - some drugs can distort the results of the Coombs test. Blood is taken using a syringe from the cubital vein, less often from the vein on back side brushes Within a few hours, the material is delivered to the laboratory.
When performing a direct Coombs test, antiglobulin serum is added to the patient's blood serum. After some time, the mixture is examined for the presence of agglutinates - they are formed if there are antibodies on the red blood cells. If the result is positive, the agglutinating titer is determined. The indirect Coombs test consists of more steps. First, antibodies present in the serum are fixed on the injected red blood cells during incubation. Then antiglobulin serum is added to the sample, after some time the presence and titer of agglutinates is determined. The analysis period is 1 day.
Normal results
Normally, the result of the direct Coombs test is negative (-). This means that there are no antibodies associated with red blood cells in the blood, and they cannot cause hemolysis. The normal result of the indirect Coombs test is also negative (-), that is, there are no antibodies to the Rh factor in the blood plasma. When preparing for blood transfusion for the recipient, this means compatibility with the donor’s blood; when monitoring pregnancy, this means the absence of Rh sensitization of the mother, a low risk of developing an immunological conflict. Physiological factors, such as dietary habits or physical activity, cannot affect the test result. Therefore, if the result is positive, a doctor’s consultation is necessary.
Diagnostic value of the analysis
A positive Coombs test result is expressed qualitatively, from (+) to (++++), or quantitatively, by titers from 1:16 to 1:256. Determination of the concentration of antibodies on red blood cells and in blood serum is performed in both types of samples. If the direct Coombs test is positive, antibodies are detected on the outer membrane of red blood cells, which lead to the destruction of these blood cells. The cause may be blood transfusion without prior typing - post-transfusion hemolytic reaction, as well as erythroblastosis of the newborn, hemolytic reaction due to the use of drugs, primary or secondary autoimmune hemolytic anemia. Secondary destruction of red blood cells can be caused by systemic lupus erythematosus, Evans syndrome, Waldenström macroglobulinemia, paroxysmal cold hemoglobinuria, chronic lymphocytic leukemia, lymphoma, infectious mononucleosis, syphilis, mycoplasma pneumonia.
A positive result of the indirect Coombs test indicates the presence of antibodies to the Rh factor in the plasma. In practice, this means that Rh sensitization has occurred, and there is a possibility of developing Rh conflict after infusion of donor blood during pregnancy. To prevent pregnancy complications, women with a positive Coombs test result are placed on a special register.
Treatment of abnormalities
The Coombs test refers to isoserological studies. Its results make it possible to identify a hemolytic reaction, as well as determine the compatibility of the blood of the donor and recipient, mother and fetus, in order to prevent the development of Rh conflict. If the test result is positive, then you need to seek advice from your attending physician - obstetrician-gynecologist, hematologist, surgeon.
An antiglobulin test, designed to detect incomplete anti-erythrocyte antibodies, was proposed by Coombs, Morant, Reis in 1945 and was later called the Coombs test. The essence this method is that antiglobulin serum containing antibodies to human immunoglobulins, when reacting with red blood cells sensitized with incomplete antibodies, leads to their agglutination.
Depending on whether antibodies are fixed on the surface of red blood cells or are in free state in blood plasma, direct or indirect sample Coombs.
A direct Coombs test is performed in cases where there is reason to assume that the red blood cells being studied are already in vivo have been sensitized with appropriate antibodies, i.e. the first phase of the reaction - the fixation of antibodies on the surface of red blood cells - occurred in the body and the subsequent addition of antiglobulin serum causes agglutination of the sensitized cells.
Using the indirect Coombs test, incomplete antibodies present in the test serum are detected. IN in this case the reaction occurs in two stages. The first stage is the incubation of test erythrocytes with the test serum, during which the antibodies contained in the test serum sample are fixed on the erythrocyte surface. The second step is the addition of antiglobulin serum.
Until now, the Coombs test is widely used in laboratory practice for the diagnosis of immunopathological conditions, in particular in autoimmune hemolytic anemia, characterized by the destruction of red blood cells due to binding cell membrane with antibodies and (or) components of the complement system. It is used to detect the presence of Ig G on the erythrocyte membrane (usually Ig G1 and Ig G3), which can activate complement, and sometimes complement (C3d). However, in acute period diseases due to the destruction of red blood cells, on which a large number of antibodies were recorded, during a hemolytic crisis, as well as with an insufficient number of antibodies during chronic course disease, a negative direct Coombs test may be observed.
It must be emphasized that the indirect Coombs test remains the best method individual selection of transfusion media, as it allows you to most accurately determine the individual compatibility of the donor and recipient by erythrocyte antigens.
An additional direct antiglobulin test for the presence of autoantibodies is recommended when examining all organ and tissue recipients in the pretransplantation period and hematopoietic stem cell recipients also after transplantation.
In addition to immunohematology and transfusiology, antiglobulin tests are widely used in the diagnosis of a number of pathological conditions: hematological diseases, including lymphoproliferative diseases, systemic diseases connective tissue, Sjogren's disease, chronic active hepatitis, etc.
Coombs tests are actively used in medical genetics and forensic medicine to determine surface erythrocyte antigens.
The Coombs test is a rather labor-intensive research method that requires special care in its implementation. When using it, there are some difficulties associated, in particular, with the interpretation of weakly positive reactions. It is known that false weak positives or negative reactions when performing Coombs tests, they may be a consequence of insufficiently effective washing of red blood cells, neutralization of the antiglobulin reagent by traces of serum, as well as contact with a non-greasy surface on which antiglobulin can be fixed, thereby losing its activity. Another disadvantage of the Coombs test is the instability of the antiglobulin reagent, the preparation and storage of which has certain features, which also makes it difficult to quantify the hemagglutination reaction with antiglobulin serum.
In addition, studies conducted by A. Holburn, D. Voak et al. , showed that the cause of false-negative results may be excessive shaking when resuspending the red blood cell suspension. Erroneous results when performing antiglobulin tests can also be caused by the presence in the antiglobulin reagent of an admixture of anti-complementary antibodies, in particular to C3d-, C3c-, C4c- and C4d- complement components, which are adsorbed on the surface of test red blood cells during incubation and create the appearance of a positive result.
These disadvantages can be easily eliminated by thoroughly washing the samples under study and monitoring the reaction conditions.
In the last decade, low ionic strength isotonic saline (LISS) has been used to reduce the time required to perform the indirect Coombs test and increase its sensitivity.
The undeniable advantage of antiglobulin tests, according to a number of authors, is their high sensitivity, which significantly exceeds their resolution. alternative methods tests that are used to detect non-agglutinating antibodies.
We compared the resolution of methods for studying blood sera for the presence of incomplete antibodies using polyglucin, gelatin and antiglobulin serum. During the study, titers of incomplete anti-D antibodies were monitored in 140 blood serum samples from isoimmune donors using gelatin, polyglucin and indirect antiglobulin tests. The formulation of these methods was carried out in accordance with generally accepted methods.
It was found that, in terms of their resolution, methods for detecting sensitization of erythrocytes by anti-D antibodies are arranged as follows: the most sensitive is the indirect Coombs test, then the gelatin test and the least informative is the polyglucin test. The results obtained in this series of experiments fully correspond to the literature data, which allows us to conclude that high level the sensitivity of Coombs tests, which makes it possible to identify with a high degree of certainty the presence in the body of anti-erythrocyte antibodies that do not cause agglutination of red blood cells.
However, when performing Coombs tests in practice, there are cases when incomplete antibodies are not detected, although the clinical picture of the disease or previous immunization indicates their possible presence. In such cases, it can be assumed that the amount of antibodies is insufficient for them to be precipitated by the antibodies of the antiglobulin serum.
This conclusion was confirmed by our own experiment, in which, using the method of analytical microelectrophoresis of cells, the presence of anti-D antibodies on test erythrocytes, which were not detected in the indirect Coombs test, was established. In this series of experiments, antiglobulin serum was added to erythrocytes pre-incubated with sera obtained from the blood of immunized donors during the period of antibodyogenesis in progress, i.e. during a period when antibodies were not detected in them using known methods, including the Coombs test.
In the studies conducted, statistical evidence of the presence of incomplete antibodies on the surface of red blood cells was provided. significant change the magnitude of the electrophoretic mobility of sensitized red blood cells after the addition of antiglobulin serum. It should be noted that anti-D antibodies were subsequently determined in all immunized donors in the indirect Coombs test in the blood serum.
Gillerand et al. also showed that antiglobulin tests are characterized by a certain sensitivity threshold: a positive result is noted only when at least 500 Ig G molecules are recorded on the surface of one red blood cell.
In addition, the literature provides evidence that a possible negative result of the Coombs test may be associated with the low affinity of antibodies that sensitize red blood cells, as a result of which they easily elute from the surface of red blood cells during the washing process.
Taking into account the above, we can conclude that in some cases a negative result of the Coombs test is not yet evidence of the absence of antibodies fixed on the surface of red blood cells.
It is known that Coombs reactions are highly specific and can detect most types of incomplete antibodies. However, as some experimental data show, antiglobulin tests can also be positive in non-immunological conditions. E. Muirhead et al. on the second day after administration of phenylhydrazine to dogs, a positive Coombs test was observed. Such a rapid appearance of a positive reaction argues against its immunological nature and, rather, is associated with nonspecific adsorption of protein on the surface of erythrocytes.
M. Williams et al. found that clavulanic acid can also cause a positive reaction, which, according to the authors, is associated with nonspecific adsorption of plasma proteins on the erythrocyte surface. A similar effect was observed during treatment with cephalosporin antibiotics.
The authors of the above studies emphasize the non-immunological nature of the positive results of Coombs tests and insist that these substances are capable of causing modification of the membranes of red blood cells, as a result of which red blood cells can adsorb proteins (in particular, albumin) that are normally present in the blood plasma and do not have properties of antibodies. In addition, it is possible that the xenobiotic, adsorbed on the cell surface, serves as a link between the cell membrane and plasma proteins.
To correctly interpret the results of antiglobulin tests, the quantitative ratio between young and mature red blood cells in the peripheral blood should also be taken into account. It was found that reticulocytes isolated from the body during the period of enhanced erythron regeneration can be agglutinated by antiglobulin serum.
Positive direct antiglobulin test result It also occurs in various pathological conditions accompanied by disorders immune system, inflammatory processes, leading to nonspecific adsorption of antibodies of different specificities on erythrocyte membranes. This suggests that Ig G molecules do not interact with specific antigens of erythrocytes, but are only fixed on the surface of the cells under study.
It should be taken into account that when performing a Coombs test in cases of diseases characterized by the development of dysproteinemia or the appearance of paraproteins, a positive result is due to the presence on the surface of erythrocytes of proteins that do not have the properties of antibodies, which also indicates the lack of specificity of antiglobulin tests regarding the nature of the protein detected with their help.
Thus, as numerous studies have shown, positive results direct and indirect antiglobulin tests are not absolute proof of the presence of antibodies, since positive reactions can also be observed in various pathological conditions not associated with isosensitization or autosensitization of the body. Therefore, only comparison of the results of several immunoserological methods with clinical picture diseases allows us to fully assess the developing pathological process.
A positive indirect antiglobulin test with a negative direct test usually indicates the presence of free alloantibodies in the test serum, associated with previous blood transfusions or pregnancies.
The Coombs test is often positive during exacerbation of paroxysmal nocturnal hemoglobinuria; a positive Coombs test with anti-C3 and anti-C3dg is a marker of cold agglutinin disease.
In cases where there is a high risk of developing hemolytic disease of the newborn, great importance To make a diagnosis (most often during pregnancy) and, if necessary, dynamic monitoring of the appearance and change in antibody titer, have the results of direct and indirect antiglobulin tests. Most often, hemolytic disease of newborns is associated with incompatibility of mother and fetus for antigen D, less often for antigens of the ABO system, and even less often for other antigens (C, c, K, etc.). Antibodies formed during this process La, being, as a rule, incomplete antibodies of the Ig G class, are clearly detected in the indirect antiglobulin test. With this disease, the correctly established titer and specificity of the identified antibodies are of great importance, since there is a certain correlation between the level of anti-erythrocyte antibodies in the blood of a pregnant woman and possible prognosis severity of hemolytic disease.
An indirect Coombs test is also necessary in clinical practice in order to ensure safe transfusion therapy. Its implementation is a mandatory component of immunohematological studies of donors and various categories of recipients, as well as routine examinations of all patients in medical institutions who may require transfusion of blood and its components.
The indirect antiglobulin test is used in the following cases:
For a more accurate determination of Rh affiliation (antigen D) in case of unclear results of determining the Rh factor by other methods (polyglucin, gelatin, etc.);
To identify weak erythrocyte antigens (Kell, Duffy, Kidd, Lewis, etc. systems) and antibodies to these antigens;
For the detection and identification of alloimmune anti-erythrocyte antibodies, including antibodies that cause hemolytic post-transfusion reactions;
To determine the presence of immune antibodies of the AB0 system during transfusion hemolytic complications;
As a compatibility test for individual selection of transfused blood and its components.
Thus, the Coombs test is an important diagnostic test used in various fields of medicine (hematology, obstetrics, rheumatology, transfusiology, clinical and laboratory diagnostics, etc.). Knowledge of the peculiarities of performing the Coombs test will help increase the reliability of the results obtained and will contribute to the correct interpretation of laboratory data.
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Of the many existing antigens in medical practice highest value focuses on three types of blood agglutinogens. One of them is the type responsible for the manifestation of the Rh factor: if it is present on the erythrocyte membrane, the blood group is diagnosed as Rh+, if absent - Rh-. If erythrocytes with Rh+ agglutinogens enter the Rh-negative blood, the body triggers an immune response and begins to produce antibodies to this antigen, which causes pathological conditions.
REFERENCE! The Rh factor is a complex multicomponent system of several dozen antigens. The most common of them are agglutinogens type D (85% of cases), as well as E and C.
The Coombs test is performed only if there is direct evidence. General list of reasons for prescribing the Coombs test:
- planning and management of pregnancy (parents have different Rh);
- donation and preparation for blood transfusion (blood mismatch according to Rh is no less destructive than mismatch according to the AB0 system);
- planned surgical intervention(in case of replenishment of blood loss with blood transfusion);
- diagnosis of hemolytic diseases.
More specific indications depend on the type of study being performed.
Direct Coombs test
The direct test detects antibodies on the surface of red blood cells. This is necessary to diagnose existing hemolytic pathologies:
- autoimmune (red blood cells and hemoglobin are destroyed as a result of an attack by the body’s own antibodies);
- medicinal ( pathological process triggers the use of certain medications such as quinidine or procainamide);
- post-transfusion (if the blood type does not match during transfusion), as well as in the form of Rh conflict during pregnancy (erythroblastosis of newborns).
REFERENCE! Hemolytic anemia is a disease associated with the premature destruction of red blood cells as a result of hemolysis, which leads to insufficient oxygen saturation of the blood and hypoxia of the brain and/or internal organs.
Hemolysis of blood elements is observed in oncological, infectious, and rheumatic diseases, therefore the direct Coombs test can be used as an additional diagnostic tool pathological condition. It is worth remembering: a negative test value does not exclude the possibility of hemolysis, but is a reason for additional examination.
Indirect Coombs test
Indirect testing is more often used to prevent pathological situations. It helps to detect antibodies in blood plasma, which is necessary for assessing transfusion compatibility and diagnosing the risks of Rh conflict during pregnancy.
More than 80% of people have a positive Rh factor (Rh+), respectively, just under 20% are Rh negative. If an Rh- mother develops an Rh+ child, her body begins to produce antibodies that attack the red blood cells of the fetus, causing hemolysis.
Taking into account the fact that the percentage of “different rhesus” marriages reaches 12-15%, the risk of hemolytic disease of newborns should be high, but in reality, only in 1 out of 25 such cases, women experience the phenomenon of sensitization (for 200 successful births there is 1 example of hemolytic pathology). This is partly due to the fact that the first Rh-positive child usually does not cause open aggression from the mother’s body; The overwhelming majority of cases occur in the second and subsequent children. The same principle applies as with conventional sensitization to a particular allergen.
There is no reaction upon first contact. The body is just getting acquainted with a new antigen, producing antibodies of the IgM class, which are responsible for a rapid immune response, but rarely penetrate the placental barrier into the child’s blood. All pathological reactions manifest themselves upon a second “meeting”, when the body begins to produce IgG class antibodies that easily penetrate the fetal bloodstream, starting the process of hemolysis.
Indirect Coombs test during pregnancy allows you to detect the presence of antibodies in the mother’s body and timely identify the initial stage of sensitization. A positive answer requires registration with a monthly antibody titer test and mandatory hospitalization 3-4 weeks before birth.
REFERENCE! Rh factor incompatibility does not affect the mother's condition in any way; hemolytic disease develops only in the child. In severe cases and in the absence of a timely response, the fetus may die in the womb or immediately after birth.
Preparation for the procedure and its implementation
Venous blood is used for diagnosis. No special long-term preparation is required for the Coombs test. Try to follow a standard set of rules before taking blood from a vein for analysis:
- give up alcohol for 3 days, medications(if possible);
- Plan your last meal later than 8 hours before taking blood for analysis;
- give up smoking, physical, mental and emotional stress within 1 hour;
- Before the procedure, drink a glass of clean still water.
The research method is based on the hemagglutination reaction.
When performing a direct test a blood sample is exposed to pre-prepared antiglobulin serum with known indicators, the mixture is kept for some time and checked for agglutinates, which are formed when antibodies are present on red blood cells. The level of agglutinates is diagnosed using the agglutinating titer.
Indirect sample Coombs has a similar technique, but a more complex sequence of actions. Antigenic erythrocytes (with Rh factor) are introduced into the separated blood serum, and only after these manipulations antiglobulin serum is added for diagnosis and agglutinate titer.
Research results
Normally both straight and indirect Coombs test should give a negative result:
- a negative direct test indicates that specific antibodies to the Rh factor associated with red blood cells are absent in the blood and cannot cause hemolysis
- a negative indirect test shows that there are also no free antibodies to the Rh factor in the blood plasma; this fact indicates the compatibility of the donor’s blood with the recipient’s blood (or the blood of the mother and child) according to the Rh factor.
A positive Coombs test indicates the fact of Rh sensitization of the body, which is main reason Rh conflict in case of blood transfusion or when carrying a child with a different Rh status. In this case, the results remain unchanged for 3 months (the lifespan of red blood cells). If the cause is autoimmune hemolytic anemia, then a positive test can follow the patient for several years (in some cases, throughout his life).
REFERENCE! Antiglobulin test is different high sensitivity, but has little information content. It does not record the activity of the hemolytic process, does not determine the type of antibody and is not able to identify the cause of the pathology. To get a more complete picture, the attending physician must prescribe additional research(blood microscopy, general and biochemical analysis, rheumatic tests, ESR, iron and ferritin levels).
The degree of sensitization can be expressed qualitatively (from “+” to “++++”) or quantitatively in the form of a titer:
- 1:2 - low value, does not pose a danger;
- 1:4 - 1:8 - the beginning of the development of an immunological reaction; does not pose a danger, but requires constant monitoring;
- 1:16 -1:1024 - a strong form of sensitization, immediate action should be taken.
Reason positive test I can be:
- transfusion of untyped blood (or with a typing error), when the Rh factor of the donor and recipient do not match;
- Rh conflict during pregnancy (if the composition of blood antigens in the father and mother do not match);
- autoimmune hemolytic anemia - both congenital (primary) and secondary, which is a consequence of certain diseases (Evans syndrome, infectious pneumonia, syphilis, cold hemoglobinuria, lymphoma);
- drug hemolytic reaction.
None of the above problems can be solved by the patient without medical care. In all cases, urgent consultation, registration or emergency hospitalization will be required.
ATTENTION! In rare cases, a false-positive Coombs test is possible. The reason for this can be frequent blood transfusions, as well as a number of diseases: rheumatoid arthritis, lupus erythematosus, sarcoidosis. This phenomenon can also be observed after removal of the spleen, as well as when the reaction is disrupted (frequent shaking of the contents, the presence of contaminants).
The Coombs test is a method laboratory research, made by influencing hemagglutination. It is based on the susceptibility of antibodies to immunoglobulins and enzyme elements, as well as their ability to agglutinate erythrocytes coated with C3 or Lg.
Direct Coombs diagnosis
Used to detect antibodies or complement components installed on the outside of cells. The direct Coombs test is performed as follows.
The use of such a sample
Direct Coombs diagnosis is used in certain cases, such as:
- transfusion effects;
- autoimmune hemolysis;
- drug-induced hemolytic anemia.
Indirect Coombs test
This diagnosis makes it possible to detect antibodies to cells in serum, which is incubated, as a rule, with donor red blood cells of type 0, and then a direct test is carried out. Apply indirect diagnosis Coombs in the following cases:
How to prepare for analysis
There are some rules for preparing for the examination.
- If the patient is a newborn, parents need to be aware that the test will help diagnose hemolytic disease of the newborn.
- If the patient has suspicions of hemolytic anemia, he should be explained that the analysis will allow him to find out whether it is caused by protective disorders, medications, or other factors.
- The Coombs test, direct and indirect, does not make any restrictions on nutrition or diet.
- It is necessary to notify the patient that the examination will require taking blood from a vein, and also tell him exactly when the venipuncture will be performed.
- You should also be warned about the possibility discomfort during the period of applying the bandage to the arm and the procedure itself.
- Drugs that can affect the sample result should be discontinued.
These medications include:
- "Streptomycin";
- "Methyldopa";
- "Procainamide";
- sulfonamides;
- "Melphalan";
- "Quinidine";
- "Rifampin";
- "Isoniazid";
- cephalosporins;
- "Hydralazine";
- "Chlorpromazine";
- "Levodopa";
- "Tetracycline";
- "Diphenylhydantoin";
- "Ethosuximide";
- "Penicillin";
- mefenamic acid.
Blood sampling is done in the morning on an empty stomach.
How the event is held
The Coombs test is carried out in the following order:
- When performing diagnostics in an adult patient, after venipuncture, blood is taken into tubes with EDTA (ethylenediaminetetraacetate).
- The newborn's blood is drawn from the umbilical cord into a beaker containing EDTA.
- The puncture area is pressed with a cotton swab until bleeding stops.
- If a bruise appears at the venipuncture site, warm compresses are prescribed.
- After blood collection, the patient is allowed to return to taking medications.
- It is necessary to inform the parents of the newborn that secondary analysis may be required to monitor the dynamics of anemia.
Advantages of the Coombs test
Such research has some advantages, namely:
Disadvantages of analysis
The positive Coombs test is a rather labor-intensive examination method, which requires a characteristic accuracy of execution. When using it, you may encounter certain difficulties, especially related to the interpretation of weakly positive effects.
It has been established that erroneous negative or weakly positive reactions during the production of Coombs tests can be the consequences of unsatisfactorily active cell washing, weakening of the antiglobulin reagent by serum residues, as well as connections with non-fat surfaces, on which antiglobulin can attach, thereby losing its effectiveness.
The Coombs test has another drawback - the low stability of the antiglobulin reagent, the acquisition and storage of which individual characteristics, which similarly makes it difficult to numerically assess the effect of antiglobulin serum on hemagglutination.
Diseases that can be detected during examination
Coombs diagnostics makes it possible to detect certain types of diseases, such as:
- hemolytic malaise of the newborn;
- various transfusion reactions;
- autoimmune hemolysis;
- drug-induced hemolytic anemia.
Today, the Coombs test is considered a fairly popular blood test system for both adults and newborns. It makes it possible to identify many different diseases.
