Reevaluation of serum-plasma differences in total cholesterol concentration.

We measured total cholesterol levels in serum and disodium ethylenediaminetetraacetate (EDTA) plasma samples obtained from 84 healthy medical students during their entrance physical examinations and 48 adults from a cholesterol screening program who were resampled because they had initial values of 5.17 mmol/L (200 mg/dL) or higher. Plasma cholesterol concentrations were 4.7% lower than those in serum samples. The plasma and serum values were highly correlated (r = .994), however, suggesting that measurements in EDTA plasma can be converted readily to equivalent serum concentrations. Thus, the negative bias in EDTA plasma was greater than the 3% value cited in the National Cholesterol Education Program Guidelines, probably because the amount of EDTA now provided in evacuated blood collection tubes is 50% greater than in those used when the 3% value was established. These findings are relevant to the interpretation of both cholesterol screening measurements and follow-up lipoprotein analyses.