Study of hemolysis interference with a peak rate nephelometric assay of lipoprotein(a)

Lipoprotein(a) [Lp(a)] is considered an independent risk factor in atherosclerosis and thrombosis. Its measurement in clinical laboratories necessitates the use of reliable methods and a strict control of preanalytical conditions. We studied here the potential interference of hemolysis on a peak rate nephelometric method. Serum samples were spiked with up to 500 mu mol/L hemoglobin (Hb), and Lp(a) was measured with a Beckman Array 360 analyzer. Hb supplementation induced a significant decrease of Lp(a) values; -15% and -25% (p < 0.01) for Hb concentrations 200 and 500 mu mol/L, respectively. Similar results were obtained when Hb addition was done before and after the manual step of sample predilution (1/5, v/v) in PEG-containing buffer. No significant difference of Hb interference was noticed according to apo(a) phenotypes. Our results indicate that hemolysis may significantly alter Lp(a) values obtained with this method, probably because of the low-dilution rate of samples. Even if this interference is of limited extent, it should be taken into account when interpretating results close to decisional values used for risk assessment. (C) 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:23-26, 2000.