CORRECTION

Abstract On page 978 of the June issue of Clinical Chemistry, the abstract appearing under #395 is incorrect. The correct abstract appears below. Automated Chromogenic Substrate Assay for Factor VIII:C Using a Microcentrifugal Analyzer. VE Cruz, SL Aleshire, CH Wallas, AJ Swett, FF Parl, CA Bradley (Clin. Path., Vanderbilt Univer., Nashville, TN 37232) Hemophilia A is a sex-linked recessive disorder characterized by a variable deficiency of Factor VIII coagulant activity (FVIII:C). The disease may be mild (5·35% FVIII:C), moderate (1-5% FVIII:C) or severe ( < 1% FVIII:C). Traditionally, FVIII:C has been measured by a clotting assay. Despite semi-automation, this method often lacks precision and accuracy. Synthetic chromogenic substrates have recently been used in coagulation studies. A chromogen is enzymatically cleaved from a synthetic peptide, measured spectrophotometrically and related to enzyme activity. One chromogenic substrate assay for FVIII:C (Kabi Diagnostica: Helena Labs. ) relics on the FVIII:C-dependent activation of FX to cleave p-nitroanilide (pNA) from the FXa-specific substrate S-2222. We adapted the Kabi chromogenic FVIII:C assay to Instrumentation Laboratory's. Multistat III Microcentrifugal Analyzer. Our assay requires 25 µl of prediluted plasma sample. 74 µl of reagent A (FIXa + PX, phospholipid and CaCl2). and 50 µl of reagent B (S-2222 plus thrombin inhibitor S-2581). Sample was first incubated with reagent A for 600 seconds at 37°, followed by addition to reagent B. After 240 seconds, the absorbance was read at 405 nm. The assay was standardized with a lyophilized assayed plasma pool obtained from the Bureau of Biologies (Bethesda, MD). Assay of a series of samples with known concentrations of FVIII:C showed the method to be linear from 1.2% to 150%. Mean recovery of FVIII:C in a range of 4.8% to 150%. Mean recovery of FVIII:C in a range of 4.8% to 150% was 102%. Precision studies made on two control pools showed the following results: Level I. X¯: 14.1%, CV: 5.1%; Level II. X¯: 148%, CV: 2.8%. Comparison with a one stage clotting assay for FVIII:C yielded a correlation coefficient of 0.94. We conclude that this chromogenic substrate assay for FVIII:C using a microcentrifugal analyszer is simple, rapid, reproducible and accurate. Small reagent volumes makes the assay economically competitive with current methods.