Seven direct methods for measuring HDL and LDL cholesterol compared with ultracentrifugation reference measurement procedures

Abstract

Background: Methods from 7 manufacturers and 1 distributor for directly measuring HDL cholesterol (C) and LDL-C were evaluated for imprecision, trueness, total error, and specificity in nonfrozen serum samples.

Methods: We performed each direct method according to the manufacturer's instructions, using a Roche/Hitachi 917 analyzer, and compared the results with those obtained with reference measurement procedures for HDL-C and LDL-C. Imprecision was estimated for 35 runs performed with frozen pooled serum specimens and triplicate measurements on each individual sample. Sera from 37 individuals without disease and 138 with disease (primarily dyslipidemic and cardiovascular) were measured by each method. Trueness and total error were evaluated from the difference between the direct methods and reference measurement procedures. Specificity was evaluated from the dispersion in differences observed.

Results: Imprecision data based on 4 frozen serum pools showed total CVs <3.7% for HDL-C and <4.4% for LDL-C. Bias for the nondiseased group ranged from -5.4% to 4.8% for HDL-C and from -6.8% to 1.1% for LDL-C, and for the diseased group from -8.6% to 8.8% for HDL-C and from -11.8% to 4.1% for LDL-C. Total error for the nondiseased group ranged from -13.4% to 13.6% for HDL-C and from -13.3% to 13.5% for LDL-C, and for the diseased group from -19.8% to 36.3% for HDL-C and from -26.6% to 31.9% for LDL-C.

Conclusions: Six of 8 HDL-C and 5 of 8 LDL-C direct methods met the National Cholesterol Education Program total error goals for nondiseased individuals. All the methods failed to meet these goals for diseased individuals, however, because of lack of specificity toward abnormal lipoproteins.

Fig. 1. Box-and-whisker plot of the differences in percentage between the direct and RMP results for HDL-C for each direct method (D, diseased group; N, nondiseased group; De, Denka; Ky, Kyowa; Ro, Roche; Sr, Serotek; Sk, Sekisui; Sy, Sysmex; Um, UMA; and Wa, Wako)

The median is the center line, the ends of the box represent 25th and 75th percentiles, the end of the lines extend to the 10th and 90th percentiles, and individual results are shown beyond the lines.

Fig. 2. Box-and-whisker plot of the differences in percentage between the direct and RMP results for LDL-C for each direct method (abbreviations as defined in the Fig. 1 legend)

The median is the center line, the ends of the box represent 25th and 75th percentiles, the end of the lines extend to the 10th and 90th percentiles, and individual results are shown beyond the lines.

Fig. 3. Percentage mean deviation from RMP values (A) and the percentage of direct method HDL-C results greater than the NCEP total error goal (B) for samples grouped by tertiles of triglycerides (TG) concentrations (abbreviations as defined in the Fig. 1 legend)

Open bars TG <0.94 mmol/L (83 mg/dL); shaded bars TG 0.94 mmol/L (83 mg/dL) to 1.60 mmol/L (142 mg/dL); striped bars TG >1.60 mmol/L (142 mg/dL). The solid lines in (A) represent the total error goal as ±13% from the RMP. Note the total error goal becomes larger at HDL-C concentrations below 1.09 mmol/L (42 mg/dL) (see footnote in Table 1), and this criterion was used in the calculation for (B).

Fig. 4. Percentage mean deviation from RMP values (A) and the percentage of direct method LDL-C results greater than NCEP total error goal (B) for samples grouped by tertiles of triglyceride concentrations (abbreviations as defined in the Fig. 1 legend)

The solid lines in (A) represent the total error goal as ±12% from the RMP.