BACKGROUND: Recently, the in vitro bleeding time test (IVBT) was proved to be a very sensitive screening method for the detection of vWD, showing rather good correlation between the closure time and the level of vWF. The vWF levels have been found to be significantly lower in healthy humans who are group O than in those who belong to the other ABO blood groups (non-group O). The aim of this study was to detect whether these differences in vWF levels in normal persons correspond to differences in nonvascular primary hemostasis when investigated by the IVBT.
MATERIAL AND METHODS: Healthy blood donors (n = 162) without evidence of hemostatic disorders, without ingestion of drugs for at least 2 weeks, and with normal in vivo bleeding time endpoints, normal factor VIII clotting activity levels, normal structure of vWF multimers, and normal ristocetin-induced platelet aggregation were examined by IVBT. IVBT was performed with two automated systems (Thrombostat 4000, VDG [TST]; and a platelet function analyzer (PFA-100, Dade Behring [PFA]). CaCl2 and ADP were used as aggregants for the two TST tests (TST-CaCl2 and TST-ADP), and ADP- or epinephrine (Epi)-coated membranes were used with the two PFA tests (PFA-ADP and PFA-Epi).
RESULTS: Closure time in the IVBT significantly correlated with the blood groups, but in reverse order (as did blood volume; data not shown): TST-ADP (mean ± SD): group O, 89 ± 14.6 seconds versus non-group O, 82 ± 13 seconds (p<0.01); TST-CaCl2: group O, 154 ± 28.9 seconds versus non-group O, 140 ± 31.3 seconds (p<0.01); PFA-ADP: group O, 91 ± 13.4 seconds versus non-group O, 86 ± 11.9 seconds (p<0.05); PFA-Epi: group O, 112 ± 15.4 seconds versus non-group O, 104 ± 16.7 seconds (p<0.05). Donors with vWF ≤77.5 % had longer closure time than those with vWF >77.5 % (p<0.05).
CONCLUSION: Significant ABO-group-specific differences in nonvascular primary hemostasis could be found by IVBT. The differences are small, however, and lie within the normal range. Whether these differences have any biologic relevance can only be speculated.