Compatibility of the Abbott IMx Homocysteine Assay with Citrate-Anticoagulated Plasma and Stability of Homocysteine in Citrated Whole Blood

Abstract

Hyperhomocysteinemia is widely regarded as a risk factor for arterial thrombosis (1)(2), and it is also implicated as a risk factor for venous thrombosis (3)(4)(5)(6). Therefore, homocysteine (Hcy) often is included in hypercoagulability evaluations (7). The Abbott IMx Hcy fluorescence polarization immunoassay instructions recommend EDTA- or lithium heparin-anticoagulated plasma or serum, whereas other coagulation tests are generally performed on citrate-anticoagulated specimens. To simplify specimen collection and avoid unnecessary phlebotomy, we investigated the compatibility of the Abbott IMx Hcy assay with citrate-anticoagulated plasma. Previous reports have suggested that acidic citrate stabilizes the Hcy concentration in whole-blood specimens for at least 6 h at room temperature (8)(9). Therefore, we also studied the stability of Hcy in whole-blood specimens collected in sodium citrate. To evaluate the correlation between citrate and EDTA Hcy values, 114 sets of paired specimens were concurrently obtained from 96 nonfasting individuals (87 healthy volunteer platelet donors and 9 patients undergoing hypercoagulability evaluation) in Becton Dickinson Vacutainer lavender-top [tripotassium EDTA (K3EDTA)] and blue-top (3.2% sodium citrate) tubes. For each patient, the citrate tube was drawn immediately before the EDTA tube, in accordance with the NCCLS guidelines. The conditions and timing for specimen collection, processing, storage, and assay performance were identical for the two anticoagulants. The specimen pairs were separated from the cells within 30 min of phlebotomy unless specimen transportation would be longer than 30 min, in which case specimen pairs were placed immediately on ice and separated from cells within 4 h. Plasma samples were then kept frozen at −20 °C or lower until blinded analysis using a standard Abbott IMx analyzer and a single lot of Abbott Hcy reagents (kindly donated by Dr. Jessie Shih, Abbott …