Direct LDL-cholesterol assay may suit fasting and nonfasting serum samples
MedWire News: Japanese research suggests that epidemiological studies can assess levels of low-density lipoprotein (LDL) cholesterol using direct homogenous assay in both fasting and nonfasting serum samples.
They found that LDL cholesterol levels measured using this method correlated significantly with those more traditionally calculated using the Friedewald formula.
National Cholesterol Education Program Adult Treatment Panel (NCEP-ATP) III categories of LDL cholesterol assessed by direct assay were also highly coincident with those determined by the Friedewald formula in fasting serum samples.
However, Kozo Tanno (Iwate Medical University, Morioka) and co-workers note that discordance increased in samples with higher triglyceride concentrations, particularly in non-fasting serum.
The Friedewald formula derives LDL cholesterol concentrations from total cholesterol, high-density lipoprotein cholesterol, and triglyceride concentrations, and guidelines for preventing atherosclerotic disease recommend its use in a fasting state, say the researchers.
Noting the difficulty of this in a clinic setting, they compared the enzymatic homogenous assay and the Friedewald formula for determining LDL cholesterol concentrations among 21,194 apparently healthy community-dwelling Japanese individuals.
All were aged 40 to 79 years, and had triglyceride concentrations of less than 4.52 mmol/l (400 mg/dl).
LDL cholesterol levels measured using the direct assay highly correlated with those by the Friedewald formula for both the 3270 fasting serum samples and the 17,924 non-fasting samples.
Concordance for NCEP-ATP III categories was 84.8% for fasting samples and 80.1% for nonfasting samples.
However, the bias between the two measurements increased in samples with triglyceride concentrations above 1.69 mmol/l (149 mg/dl), with LDL cholesterol concentrations calculated using the direct assay tending to be slightly higher.
The difference in measurements was particularly noticeable in nonfasting samples, the authors note in the journal Clinica Chimica Acta.
Nonetheless, they conclude: "The findings suggest that the direct assay for LDL cholesterol measurement can be used in epidemiological studies on the association of LDL cholesterol with risk for cardiovascular disease both in fasting and nonfasting samples."
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By Anita Wilkinson