Study Exposures
Our hypothesis was the greater vitamin B12 or folate deficiency in patients with VVS than in controls. Therefore, we measured serum levels of vitamin B12, folic acid, and homocysteine, a metabolite that its increase indicates functional vitamin B12 or folate deficiency. Blood samples were drawn from the case group after inserting the intravenous line as a routine preparation for HUTT and before conducting the test. Blood samples of the control group were drawn during standard procedures of TeCS. Participants were instructed to fast for at least eight hours prior to blood sampling. All blood samples were handled in dark containers designed for light-sensitive biochemicals, centrifuged a few hours after sampling, and stored at -80˚C. The analyses were done using Abbott Diagnostic chemiluminescence kits.
Vitamin B12 deficiency was defined as serum vitamin B12<187 pg/mL, and folate deficiency was defined as serum folate<3.1 ng/mL. Increased serum levels of homocysteine may indicate a functional deficiency of either vitamin B12 or folate.20 Thus, we defined another variable named vitamin B12/folate deficiency defined as serum homocysteine>16.2 and >13.6 µmol/L in males and females, respectively, or vitamin B12 deficiency, or folate deficiency.