**9.1 Tests carried out in case of suspected early hemolytic transfusion reaction**

Laboratory tests—mainly serological—are crucial for the diagnosis of an early haemolytic reaction. The type of laboratory tests performed for early transfusion haemolytic reactions is shown in **Table 7**.

The basic serological examination consists of direct antiglobulin testing (DAT); determination of blood group and RhD in donor and recipient; repetition of the serological compliance test. A test should be performed for the presence of antibodies in the recipient before and after the transfusion. Positive DAT indicates haemolysis of red blood cells of immunisation origin. A negative DAT result does not exclude haemolysis, it may mean that the transfused blood cells have been destroyed by alloantibodies or the method used is not very sensitive. Alvarez et al. [60] compared the sensitivity of DAT performed by technique using monospecific IgG antiglobulin, flow cytometry and antibody elution. The study showed that DAT could only indicate 10% of antibody coated cells [61]. Performing DAT in the red blood cell eluate, its sensitivity was 1%. Flow cytometry proved to be a similarly sensitive method.

The re-determination of the ABO and RhD blood group of the recipient before and after the transfusion and in the donors' blood will exclude errors in the identification of the recipient or blood sample (wrong blood in tube (WBIT)). Test results carried out by Biomedical Excellence for Safer Transfusion Working Party of The International Society for Blood Transfusion in 10 countries with 62 institutions,


**Table 7.**

*Type of laboratory tests and the location of their performance in the case of early transfusion reaction.*


**Table 8.**

*Changes in laboratory indicators in haemolytic transfusion reactions [56].*

which examined a total of 690,000 blood samples, showed that the frequency of WBIT is 1 in 165. In two countries, Sweden and Finland, which have implemented national identification systems, this frequency was 1 for 1986 samples [61].

All-antibody screening for recipients is generally performed using routine testing on standard blood cells. A panel of standard cells should contain clinically important antigens in a homozygous form to detect the presence of weak antibodies. The test should be performed on serum/plasma samples taken before and after transfusion. If positive results indicate alloantibodies are present, they should be identified. Detection of a specific antigen on the donor's blood cells is the confirmation that the detected alloantibodies were responsible for the haemolytic transfusion reaction. If negative results are obtained, additional tests should be performed, for example, PTA PEG, polybrene test and PTA NaCl test. If negative results persist, the test should be repeated after a week and after 2 weeks, as in some patients, the antibodies may have been consumed to destroy transfused incompatible red blood cells.

Laboratory tests that help to differentiate haemolysis include determination of free haemoglobin in the blood and urine, haptoglobin and lactate dehydrogenase (LDH) and bilirubin. While interpreting the obtained test results, it should be kept in mind that haemolysis or shortening the survival time of red blood cells can be caused by non-immunological factors, for example, adding hypotonic fluids to red blood cells, inefficient heating or freezing devices, etc. [62]. **Table 8** presents changes in laboratory indicators in transfusion haemolytic reactions [56].
