Humoral rejection caused by the presence of HLA- specific complement- binding antibodies remains to be an obstruction in transplantation medicine. To achieve the best possible transplantation results and avoid futile transplantation attempts resulting in graft failure, a pre-transplant evaluation of the patients’ sera is done to recognize and eliminate possible risk factors, in this case complement- binding antibodies against HLA- antigens. The currently used methods for the detection of such antibodies are the gold-standard complement-dependent cytotoxicity test and the Luminex based single antigen bead assay, which shows better sensitivity and specificity. The new C1q-Screen Kit, established by One Lambda, US, is, according to the company, able to combine the advantages of both methods in one single test. It could serve as a possible alternative at the Department for Blood Group Serology and Transfusion Medicine at the Medical University of Vienna, Austria. The aim of this study will be comparing the results of 30 patients’ sera, which were tested with the C1q-Screen, the complement- dependent cytotoxicity and Luminex- based single antigen bead assay. The test results were matched using HLA- Loci and specificity, as well as HLA- class and mean fluorescent intensities of each detected antibody. The C1q- Screen assay showed good correlation with Luminex Single Antigen Bead Assay (~43%), in comparison to cytotoxicity test more cytotoxic HLA- antibodies could be detected with C1q- Assay; that could be, however, a hint for higher sensitivity, but this higher sensitivity and their clinical relevance could not be confirmed within this study.