An application of apo(a) isoforms for the clinical assessment of Lp(a)

To examine whether or not Lp(a) is applicable as a diagnostic marker for at herosclerosis, we studied the correlation between Lp(a) levels and molecula r weights of apo(a) isoforms in sera from both normal healthy adults and di abetic patients. Serum Lp(a) level was measured by turbidimetric immunoassa y (TIA) and the molecular weight of apo(a) isoform was determined by Wester n blotting analysis. The serum Lp(a) levels of the diabetic patients (25.0 mg/dl +/- 2.2 [mean +/- SE], n = 54) were significantly higher than those o f the normal subjects (14.4 mg/dl +/- 0.57, n = 500). With respect to the c orrelation between serum Lp(a) levels and the molecular weights of apo(a) i soforms, there was an inverse correlation in sera from normal subjects (n = 298), whereas there was no correlation in sera from the diabetic patients. Statistical significant inverse correlation (r = -0.91, y = 224.25 - 3.07x ) was especially observed in 50 representative apo(a) isotypes from the nor mal subjects, By applying a standardized curve based on the significant inv erse correlation to serum Lp(a) levels, 40.7% (22/54) of the diabetic patie nts were revealed to have an abnormally high value of serum Lp(a). Moreover , it was found that the significantly higher mean value of serum Lp(a) in t he diabetic group was caused by the 22 patients with higher value of Lp(a), The present findings suggest that determination of apo(a) isoform size pro vides estimation of the serum Lp(a) value and that the inverse correlation curve between serum Lp(a) level and the molecular weight of apo(a) isoform may be applicable to the clinical use of Lp(a). J. Clin. Lab. Anal. 14:53-5 8. 2000. (C) 2000 Wiley-Liss, Inc.