Pre-analytical, analytical and biological sources of variation of lipoprotein(a).

The pre-analytical, analytical and biological sources of variation were estimated for serum lipoprotein(a) concentrations, as measured with a new commercially available procedure. There were no significant differences between the concentrations of lipoprotein(a) measured in EDTA plasma and serum. The analyte is stable in specimens stored for up to two weeks in the refrigerator, or up to three months at-20 degrees C. Fasting is not essential before the lipoprotein(a) determination. Data on analytical (between-run coefficient of variation < 15.7%), within-subject (8.6%) and between-subject variation (85.8%) were used to calculate the analytical goal for imprecision (< 4.3%), the critical difference between serial values from an individual that represents a significant change (36.3%), the number of specimens which should be collected to estimate the homeostatic value for an individual to within +/- 5% (26), and to establish the marked individuality of lipoprotein(a) (index of individuality, 0.1).