Cut-off levels based on deviation from standard negative control is better than moderate level based on fixed cut-off for ACA assessed using ELISA for the diagnosis of antiphospholipid syndrome.

Aim: To assess the consistency of the standard negative control of IgG and IgM ACA levels within runs and batches of tests, and levels of ACA agreement between those established according to deviation from standard negative control and those established based on a fixed level cut off.

Methods: Serum samples of 148 patients who presented an INR < 0.9 or prothrombin activity of > 130% or aPTT below 0.