In the direct determination of the ABO group, the patient’s RBCs are tested against known antisera. The presence of the antigens (agglutinogens) present on the surface of the red cells is detected by the agglutination that occurs after contact with the antisera. A positive reaction (agglutination) indicates that the corresponding antigen is present on the surface of the red cells under examination. In the indirect determination of the ABO group, the patient’s serum (or plasma) is tested against red blood cells of a known group. The patient’s serum contains natural antibodies (agglutinins IgM) against anti gens that are not present on the surface of their own red cells. A positive reaction (agglutination) indicates that antibodies are present in the serum, and therefore the relative antigen is missing on the surface of the red cells. Figure 1 shows direct and indirect ABO group analysis with RHD type determination.

Fig1. Determination of the direct and indirect ABO Group, with RHD type determination; some examples. The first sample reacts with the anti-A and anti-AB sera, does not react with the anti-B serum, it reacts with the anti-D sera (both Dvi− and Dvi+), plasma reacts with group B but not group A red blood cells, therefore the subject is A D positive. The second sample does not react with the anti-A serum, but reacts with the anti-B and anti-A sera, B, reacts with the anti-D sera (both Dvi− and Dvi+), plasma reacts with group A but not group B red blood cells. It is, therefore, a B D positive. The third sample reacts with the anti-A, anti-B and anti-A,B sera, does not reacts with the anti-D sera (both Dvi− and Dvi+), plasma does not react with group A and group B red blood cells. It is therefore a subject of AB D negative group. The fourth sample does not react with the anti-A, anti-B, anti-A,B sera, such as with the anti-D sera (both Dvi− and Dvi+), plasma reacts with group A and group B red blood cells. It is, therefore, a subject of group O D negative

In rare cases, subjects who do not react with anti-A, anti B and anti-A, B sera strongly agglutinate the red cells of group O. If this agglutination is not due to the presence of cold agglutinins (in this case it disappears completely after 5 minutes at 37 °C), it could be the so-called Bombay phenotype (hh), an exceptional finding.

Weak variants of A and B are known. The best known A2 reacts well (4+) with anti-A, B sera and weaker (2+) with anti-A sera, does not react with anti-A lectin. A1 but reacts well with anti-H lectin. Natural anti-B antibodies are always present in the serum, and in 2–3% of cases anti-A antibodies may be present which react with group A1 red cells but not with group A2 ones. The variants called A3 and B3 have the characteristic of reacting very weakly with the anti-A and anti-B sera (respectively), while they react well with the anti A, B serum. The expected natural antibodies are present in the serum of these subjects.

From these observations it follows that the ABO group must be determined using always and, on all samples, complete anti-A, anti-B and anti-A, B sera. The search for “natural” antibodies in the serum must be carried out using at least group A1 and B red blood cells.

There may be discrepancies between direct and indirect determination of the ABO group, mostly attributable to technical causes or anomalies present in the sample.

Technical causes: False negatives may be attributable to failure to add a reagent, errors in interpretation or registration (hemolysis) of the results, incorrect relationship between red blood cells and antisera, too low working temperature. False positives can be due to excessive centrifugation, use of contaminated reagents, misinterpretation or recording of results.

Sample anomalies: Interferences with the direct test can be observed in patients recently transfused with nonhomo group red blood cells (i.e., red blood cells O to a recipient A) or with weak subgroups of A or B, in case of poly agglutination of the red blood cells, presence of Wharton’s gelatine in umbilical cord) or high concentrations of abnormal proteins (myeloma), cold agglutinins. Interference with the indirect test can be observed in specimens with clots, presence of alloantibodies to erythrocytes, auto-antibodies to erythrocytes, immunosuppressed patients, children under 6 months. Transplanted with ABO-incompatible allogenic marrow, recent transfusions with nonhomo group plasma. Figure 2 shows direct ABO determination with evidence of a double red cells population.

Fig2. Direct ABO determination with evidence of a double red cells population. This is a sample from a B group patient that in emergency room received two units of O group packed red cells. In the anti B column are present two RBC population: the patient’s B RBC (top) and the transfused O RBC (bottom) of the tube

Search and titration of immune or natural anti-A and anti B antibodies is done primarily to support ABO incompatible solid organ and hematopoietic stem cells transplant programs. The titration of anti-A and anti-B is carried out by diluting the serum to the doubling in saline and evaluating the reaction after immediate centrifugation. The last dilution of the serum in which hemolysis and / or agglutination is highlighted determines the titer of the hemolysins or anti-A and anti-B agglutinins. Subjects with high titer (>1/128) of anti-A and anti-B have antibodies of an immune nature alongside the natural ones. Search for anti-A and anti-B immune antibodies can be carried out with the same method after denaturation of the IgM with 2-mercaptoethanol. Alternatively, two doubling dilutions of the serum can be prepared, one incubated at 37 °C and the other at 4 °C. The difference in the titer (always greater in that incubated at 37 °C) will be attributable to the presence of IgG. Group O subjects naturally have IgG class anti-AB.

اخر الاخبار

اخبار العتبة العباسية المقدسة

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لطلبتها وملاكاتها جامعة الكفيل تواصل تنظيم الورشة التدريبية للإسعافات الأولية استعدادًا لزيارة الأربعين

مصنع الجود للمحاليل الوريدية: نحرص على إنتاج دواءٍ آمن وفعّال بأيدٍ وطنيّة دعمًا للقطّاع الصحي العراقي

المزيد

الآخبار الصحية

"شعور لا مفر منه" في الحياة يهدد حياة الملايين بالموت المبكر!

أعراض للخرف قد تظهر في المشي.. كيف نكتشفها؟

ماذا يحدث لسكر الدم عند شرب القهوة؟

سرطان القلب.. لماذا يعد من أندر أنواع السرطانات؟

المزيد

الآخبار التكنلوجية

صهر أردوغان يطلق منصة تواصل جديدة.. تنافس فيسبوك ؟!

غوغل تطلق "مرشد الويب" لتنظيم نتائج البحث بالذكاء الاصطناعي

بعد 20 عاما.. رصد أصغر أفعى في العالم مجددا في بربادوس !

ذكر أم أنثى؟.. دراسة تنسف الاعتقاد الشائع حول جنس المولود

المزيد

مواضيع ذات صلة

Partial thromboplastin time, activated (APTT, Partial thromboplastin time [PTT])

parathyroid scan (Parathyroid scintigraphy)

parathyroid hormone (PTH, Parathormone)

Paracentesis (Peritoneal fluid analysis, Ascitic fluid cytology, Peritoneal tap)

Clinical Immunology Laboratory (Diagnostic Testing)

Determination of Type D and Rh Phenotype

Platelet and Granulocyte Antigens and Antibodies

pancreatobiliary fish testing

pancreatic enzymes (Pancreatic secretory test, Amylase, Lipase, Trypsin, Chymotrypsin)

pancreatic elastase (PE, EL1, Elastase-1, Fecal Elastase)

Trends in Immunoassay Automation

Flow Cell Cytometry