To the Editor.
—Cloey et al1 reported that the mean cholesterol concentration in plasma samples prepared with disodium EDTA (ethylenediaminetetraacetic acid) was 4.7% lower than the mean cholesterol concentration in serum samples. The difference they observed is larger than the previously established value.2,3 However, Lipid Research Clinics Laboratory Methods Committee2 reported mean plasma cholesterol concentrations that ranged from 1% to 4% lower than the mean serum cholesterol concentration. The reevaluation report1 suggested that the increased difference was due to a higher concentration of disodium EDTA, now routinely used in blood collection tubes.We drew blood samples from 110 patients (aged 53 ± 14 years) who presented for lipoprotein analysis. Samples were collected with Vacutainer Systems collection tubes, (Becton-Dickinson, Rutherford, NJ) and the collection order of the paired serum and plasma specimens was alternated. Disodium EDTA tubes (final concentration, 4.46 mmol/L) were completely filled and mixed.
Wickus GG, Dukerschein RO. Serum-Plasma Differences in Total Cholesterol: What Correction Factor Should Be Used?. JAMA. 1992;267(2):234-235. doi:10.1001/jama.1992.03480020044024