Electrophoretic measurement of lipoprotein(a) cholesterol in plasma with and without ultracentrifugation: comparison with an immunoturbidimetric lipoprotein(a) method.

OBJECTIVES: Elevated plasma lipoprotein(a) [Lp(a)] is a significant risk factor for vascular disease. Standardization of Lp(a) mass measurement is complicated by the heterogeneity of apolipoprotein(a) [apo(a)]. We investigated whether Lp(a) cholesterol measurement, which is not influenced by apo(a) size, is a viable alternative to measuring Lp(a) mass. DESIGN AND METHODS: Plasma Lp(a) cholesterol was measured electrophoretically, with and without ultracentrifugation, and results were compared to each other and to immunoturbidimetrically measured Lp(a) mass in 470 subjects. RESULTS: Ultracentrifuged and whole plasma Lp(a) cholesterol levels demonstrated high correlation (R = 0.964). All samples with detectable (>/=2.0 mg/dl) Lp(a) cholesterol had Lp(a) mass >30 mg/dl (the clinically relevant cutpoint), while 59 samples with Lp(a) mass >30 mg/dl did not have detectable Lp(a) cholesterol. CONCLUSIONS: Lp(a) cholesterol can be measured in whole plasma without interference from VLDL lipoproteins. The relative clinical merits of measuring Lp(a) cholesterol vs. Lp(a) mass or both in combination deserves investigation.

Gender differences in C-reactive protein concentrations-confirmation with two sensitive methods.

Two new automated, highly sensitive methods for the measurement of C-reactive protein (CRP) were compared using blood samples from active and retired health care workers (116 males, 114 females). The regression equation was y=1.115x-0.0267 forthe Kamiya K assay immunoturbidimetric method (x) vs. the Behring BNII nephelometric method (y) with medians (IQR) of 0.156 (0.081 to 0.276) and 0.150 (0.060 to 0.240) mg/dl, respectively. Significant differences in hsCRP values between males and females were observed (p=0.013 and p=0.0018 for Behring and Kamiya methods, respectively). This gender difference in CRP levels was confirmed by analysis of serum samples from 1,114 individuals (639 males and 475 females) obtained through Mayo Medical Laboratories reference services, which represents participants from across the United States. The gender difference, which was confirmed (p<0.0001), was independent of age differences as assessed by multiple regression analysis. The observed gender differences have important implications for the establishment of cut-off points for cardiovascular risk stratification.