Coombs test

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Schematic representation. Above, direct Coomb test : recipient or patient erythrocytes have antibodies on their cell membrane and are incubated with the Coomb serum. As a result, the red blood cells clump together. Indirect Coobstest below : recipient or patient serum contains (non-clumping) antibodies of the IgG type . For this purpose, donor erythrocytes (blood to be transfused) are given. The free serum antibodies bind to the donor erythrocytes and agglutination occurs after the addition of the Coombs serum.

The Coombs test, also antihuman globulin test (short: AHG test ), rarely also Race Coombs test (according to Robert Russell Race ), subsumes two tests named after the Cambridge pathologist Robin Royston Amos Coombs based on rabbit antihuman globulin (antibody against immunoglobulin ). They are used to detect so-called incomplete (i.e. non-clumping) antibodies ( IgG ) against red blood cells ( erythrocytes ), which cannot cause agglutination of erythrocytes on their own. These antibodies of the IgG class are also known as “incomplete” antibodies. On the other hand, the antibodies of the IgM class are able, due to their pentamer structure, to cause agglutination of the erythrocytes even without adding a reaction enhancer and are therefore also called complete antibodies.

The Coombs test was described by Carlo Moreschi (1876–1921) in 1908, but was not further developed and used by Robin Coombs until the mid 1940s.

As part of an indirect Coombs test, the so-called Coombs serum or anti-human globulin (leporoidal antibodies against human IgG antibodies) and complement components are used as reaction intensifiers to detect the antibodies. Coombs serum is obtained from the serum of rabbits which have been immunized against human antibodies of the IgG class. Since there is also the direct Coombs test in addition to the indirect Coombs test, the terms 'Coombs tests' are not to be equated with the ' antibody test '.

They are used in hematology to diagnose haemolytic anemia , for example in newborns with rhesus incompatibility . Transfusion medicine they use in serological compatibility study, short and cross matching of blood products .

Direct Coombs Test (Direct Anti-Human Globulin Test, DAT, Direct AHG)

The direct Coombs test can be used to provide immunohematological evidence of whether the patient's erythrocytes are loaded with incomplete antibodies (immunoglobulins or complement factors ). The direct Coombs test is used to detect in vivo loading by sensitizing patient or newborn erythrocytes, with irregular blood group antibodies or complement. The indications for a direct Coombs test:

  • if a transfusion incident is suspected,
  • suspected haemolyticus neonatorum disease , the breakdown of erythrocytes in the fetus due to a blood group incompatibility between mother and child,
  • if autoimmune hemolytic anemia is suspected, i.e. the destruction of red blood cells by the body's own production of antibodies that direct their activity to its own erythrocytes,
  • in the case of a positive self-sample in the indirect Coombs test.

For the immunohematological examination, polyspecific Coombs sera are used; they are monoclonal or polyclonal . They contain antibodies that react with immunoglobulins as well as with complement factors with which the erythrocyte membranes are loaded.

Indirect Coombs test (indirect anti-human globulin test, IAT, indirect AHG)

The indirect Coombs test detects unbound antibodies that are circulating in the serum . The test is particularly important for the detection of incomplete antibodies in the mother's serum in the case of rhesus incompatibility . See also antibody search test . The indirect Coombs test is carried out in two laboratory clinical steps. In the first step, the blood plasma to be examined is incubated with defined test erythrocytes . If the examined patient serum contains antibodies, binding to the test erythrocytes occurs, but not agglutination. Only in the second step, when the Coombs serum is added to the previously treated (incubated) test erythrocytes, does agglutination occur if the results are positive.

The indirect Coombs test is used in cases of rhesus incompatibility for the detection of incomplete, circulating antibodies in the mother's serum.

However, the Coombs test can also be positive for no apparent cause (idiopathic). Coombs negative hemolytic anemias may exist. a. in paroxysmal nocturnal hemoglobinuria , in Wilson's disease , and in hereditary diseases such as thalassemia .

The indications for an indirect Coombs test are:

  • when determining blood groups, more precisely, as an integral part of the so-called antibody search test,
  • when preparing blood transfusions for patients who have already been transfused frequently, so-called polytransfused patients,
  • in the case of anamnestic or clinical suspicion of immunized persons due to pregnancy or previous transfusions,
  • for maternity check-ups between the 4th to 8th and 24th to 27th week of pregnancy ,
  • in the case of anamnestic and clinical suspicion of rhesus incompatibility or intolerance,
  • in oncological patients who are to receive a blood transfusion,
  • if autoimmune hemolytic anemia is suspected.

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Individual evidence

  1. ^ Carlo Moreschi, Università degli Studi di Pavia [1]
  2. ^ Carlo Moreschi: New Facts About Blood Cell Agglutinations. Zbl. Bakt. 46, 49, 456 (1908)
  3. ^ Christian Mueller-Eckhardt, Volker Kiefel: Transfusion Medicine. Basics - Therapy - Methodology . 3. Edition. Springer-Verlag, Berlin / Heidelberg 2004, ISBN 3-540-00991-4 , pp. 161 ( limited preview in Google Book search).
  4. ↑ Example: Instructions for use AHG blend diagnostics Polyspecific Coombs serum, sd-nostik.de [2]
  5. ↑ John P. Greer et al. (Ed.): Wintrobe's Clinical Hematology . 12th edition. Lippincott Williams & Wilkins, Philadelphia 2009, ISBN 978-0-7817-6507-7 , pp. 1011 ( limited preview in Google Book search).
  6. ↑ For medical professionals. EuroWilson, September 18, 2009, accessed March 6, 2014 .