Measurement of lipoprotein (a): comparison of Macra and Imubind methods.

Our specific aim was to compare lipoprotein(a) [Lp(a)] measured by two enzyme-linked immunosorbent assays (the Strategic Diagnostics, Inc. Macra Lp(a) and the American Diagnostica, Inc. Imubind Lp(a) Stripwell) in sequentially referred hyperlipidemic patients. The Macra method binds Lp(a) in serum or plasma to monoclonal anti-Lp(a) in microtiter test wells followed by polyclonal anti-Lp(a) and a chromogenic reaction; the Imubind method is similar but uses two polyclonal anti-Lp(a) antibodies. Within run coefficients of variation were 1.5 percent for the Macra (Lp[a] 27.2 +/- 0.4 mg/dl) and 3.4 percent for the Imubind method (Lp[a] = 18.9 +/- 0.6 mg/dl). Between-run coefficients of variation for the Macra method were 4.7 percent (Lp[a] 14.8 +/- 0.7 mg/dl) and 8.3 percent (Lp[a] of 33.5 +/- 2.8 mg/dl). For the Imubind method in nine separate analytical runs, the between run coefficients of variation were 8.4 percent (Lp[a] of 15.4 +/- 1.3 mg/dl), 3.0 percent (18.8 +/- 0.6 mg/dl), and 5.7 percent (25.6 +/- 1.5 mg/dl). The intraclass correlation was 0.92 (p < or = 0.0001) for duplicate aliquots (n = 210) quantitated by both methods, and the lower limit of the 95 percent confidence interval of the intraclass correlation was 0.90. Comparison of the two methods revealed no systematic bias (p = 0.09), since the lower limit of the 95 percent intraclass correlation confidence interval was > or = 0.75, the two methods for measuring Lp(a) are considered interchangeable. Given the importance of Lp(a) as an independent risk factor for coronary heart disease, it is clinically important to have precise and accurate methods for its measurement.