Blood compatibility testing is elementary for the safety of red blood cell transfusions. It typically consists of three steps: blood typing, antibody screening / identification, crossmatching. The sensitivity and specificity of today's tests for alloantibodies are very high, which has reduced the risk of acute hemolytic transfusion reactions (AHTR). But, there are situations in which alloantibodies can't be completely excluded. Anti-CD38 monoclonal antibodies and panreactive autoantibodies can mask alloantibodies. To reduce the risk of AHTR, recommendations by expert panels have been published (eg, DTT assay, antigen-matched blood transfusion). Additionally, a careful clinical surveillance of the patient during a transfusion is essential and the "biological test", introduced by Franz Oehlecker in the 1930ies, could be helpful in reducing the risk of serious AHTR in cases of a positive crossmatch and situations when relevant alloantibodies can't be excluded.

This survey in German speaking countries seeks to evaluate the current use of the "biological test" in clinical routine by institutions that are involved in blood transfusion. The survey was distributed by E-mail notification to all DGTI members. It consists of two questions: 1: "Is the "biological test" (Oehlecker's test) included in your transfusion recommendations?". 2: "Have you implemented a diagnostic method for the detection / exclusion of an acute / delayed hemolytic transfusion reaction ("in vivo hemolysis test")?".

We received 14 questionnaires until 30 April 2024 (9 institutes of transfusion medicine (ITM), 3 blood banks (BB), 1 blood donation services (BDS), 1 doctor's office). 9/14 (64.3%) participating institutions recommend a "biological test" under certain circumstances. These recommendations include specific transfusion protocols and the clinical examination for transfusion reactions. Additionally, 4/14 (28.6%) participants recommend laboratory tests for the detection of hemolysis ("hemolysis test").

The biological test is used in clinical routine. Most participants use certain transfusion protocols, but also laboratory methods for the detection of hemolysis are implemented. To evaluate the impact of the biological test for the prevention of serious hemolytic transfusion reactions, further prospective investigations are necessary, but complex (low-intervention clinical trial).

The authors declare no conflicts of interest.