Background. Defining the clinical relevance of donor-specific HLA antibodies (DSA) detection by Luminex single-antigen (LSA) flow beads assay is critical in monitoring posttransplant outcome. Methods. Sera of kidney transplanted patients were tested by LSA1 and LSA2 with One Lambda Labscreen (test 1) and Immucor Lifecodes (test 2), at the time of a graft biopsy. The first group (G1, n = 50) had a biopsy highly suggestive of humoral rejection, and the second (G2, n = 50) had no criteria of rejection. Positivity criteria for DSA was mean fluorescence intensity greater than 500 for test 1, whereas specificity assignation respected the provider’s recommendations for test 2. Results. In G1, we identified at least 1 DSA in 44 patients with test 1, and in 39 patients with test 2. In G2, test 1 identified at least 1 DSA in 16 (32%) patients and test 2 in 7 (14%) patients. Sensitivity and specificity for antibody-mediated rejection diagnosis was 88% and 68%, respectively, with One Lambda, and 78% and 86%, respectively, with Immucor. Correlation and agreement were found in class I and II between intensity parameters of the 2 manufacturers. The use of the sum of the intensity of DSA improved the sensitivity and specificity of the 2 tests. Conclusions. We report the first comparative study of the 2 Luminex assays available for detecting DSA in the postkidney transplant setting. Although there is a good correlation and reliability between the 2 assays, significant differences exist. Positivity criteria for DSA determination differ and interpretation should take these specificities into account.