Evaluation of anticoagulants for serologic assays of cholera vaccination

Blood collected with an anticoagulant is beneficial for simultaneous evaluation of immune cells and humoral components such as antibodies. However, it is critical that the anticoagulant does not affect quantitative and qualitative analyses of antibodies. In the present study, we examined the potential interference of the widely used anticoagulants heparin, EDTA, and acid citrate dextrose (ACD) on vibriocidal antibody activities and Vibrio cholerae lipopolysaccharide (LPS)-specific IgG, IgM, and IgA levels in the plasma and sera obtained from cholera patients or vaccinees. Serum vibriocidal antibody titer was inhibited in the presence of EDTA or ACD but not in the presence of heparin. Moreover, 100% (8/8) of the vibriocidal antibody titers of plasma samples obtained from the vaccinees in tubes containing heparin were identical to the titers of matched sera when compared with 37.5% (3/8) and 50% (4/8) of the plasma samples prepared with EDTA and ACD, respectively. Among LPS-specific Igs, the Pearson correlation coefficient (r) for IgA in serum and plasma was low (r = 0.716), and the coefficients for IgG and IgM were relatively high (r = 0.997 and r = 0.945, respectively) in heparinized plasma samples compared with the coefficient for IgG and IgM of EDTA- and ACD-treated plasma. Our results suggest that heparin is an appropriate anticoagulant for the collection of blood when measuring vibriocidal activities and antibody levels in plasma samples.