Influence of Low-DensIty- Llpoprotein Particle ... - Clinical Chemistry

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mara et al. (3). The sera were sepa- rated into two fractions. (LDL. + HDL, ... J, Wilson PWF, Schaefer LI. Ef- feet of gender, age, and lipid status on low density.
Influence of Low-DensItyLlpoprotein Particle Size on Measurement of Apollpoproteln

different g/L (2.44

L), respectively].

B

To the Editor: Radial immunodiffusion (RID) has been applied widely to assay apolipoprotein (ape) B, mainly in low-density lipoprotein (LDL). This technique, however, has several drawbacks (1). For assay of apo B by RID, the standards to be used must have a particle size comparable with that of the lipoproteins to be assayed (2). In fact, however, the particle size of human

LDL appears to be heterogeneous (3), whereas that of standard LDL is generally homogeneous. Thus, the results of apo B assay in LDL by RID may be influenced by the heterogeneity of

LDL particle

size.

To test this hypothesis, we exammed the effect of LDL particle size on the relation between apo B measured by RID and apo B measured by rate immunonephelometry (INA) in 88 samples of fasting serum from 44 pa-

tients

with type fib hyperlipoproteine-

mia (serum cholesterol 8 mmol/L, serum triglyceride 2 mmolIL). Fortyfour sera were taken before diet or lipid-lowering drug therapy and another 44 sera were obtained during treatment with diet (15 samples), simvastatin (16 samples), or gemfibrozil (13 samples). To measure LDL particle size, we subjected 5 L ofserum to 2-16% polyacrylainide gradient gel (Pharmacia LKB, Uppsala, Sweden) electrophoresis as described by McNamara et al. (3). The sera were separated into two fractions (LDL + HDL,

and VLDL)

by ultracentnifugation

the median

size was above value

the small 46) and the large LDL particle group (group B; ii 42). In group A, mean (± SD) apo B concentrations measured by INA and by RiD were not significantly

LDL particle

group

=

(23.5

or below

nm):

(group

A; n

However,

in group B,

mean ape B concentrations measured by INA were significantly (P