Effect of freeze/thawing cycles on the plasma concentration of TAC. Ten different plasmas, collected on K-EDTA were assayed for TAC following the manual method described in the Material and Methods section. In A, different plasma volumes were assayed after 1–4 freezing cycles. In B, the calculated TAC concentration per μl of plasma was reported over the number of freezing cycles. Mean ± SEM of 10 different plasma samples, from normal individuals.