Von Willebrand factor (vWF) antigen levels and function in healthy Thais

Type I von Willebrand disease (vWD) is very common in caucasians. Its genetic basis is possibly heterogenous, lying both within and out of the vWF gene locus. We sought to investigate vWF levels in the Thai population, to compare with those of western countries. The vWF antigen and activity were measured using ELISA and Collagen Binding Assay (CBA), respectively, in 311 healthy Thai volunteers. The mean age was 32.3, ranging from 18 to 75 years. Fifty-four percent were female. Low vWF antigen and activity (below 50 U/dl) were found in 3.5% and 10.2%, respectively. Around 75% and 20% of these cases had O and A blood groups, respectively. Three (0.96%) had definitely low levels of vWF (vWF antigen level below 35 U/dl), suggesting the diagnosis of vWD. Similar to previous studies, vWF levels were lowest in subjects with group O blood. We found that subjects with blood group A had higher vWF levels than group O subjects, but significantly lower vWF levels than those with group B. The average ratio between the vWF activity and antigen was 0.96, ranging from 0.66 to 1.66. These ratios were inversely correlated with age (p=0.047), suggesting a decline in vWF activity per vWF protein with advancing age. Low levels of vWF are common in healthy Thais. Clinicians should be aware of vWD in bleeding patients and beware low levels of vWF in therapeutic plasma products, especially from blood groups O and A.