COMPARISON OF LP(A) LEVELS IN FRESH AND FROZEN PLASMA USING ELISAS WITH EITHER ANTI-APO(A) OR ANTI-APO-B REPORTING ANTIBODIES

Sandwich ELISAs with an anti-apo(a) trapping antibody and either an an ti-apolipoprotein B or anti-apolipoprotein(a) reporting antibody, were used to measure the concentrations of Lp(a) in 230 plasma samples tha t were either freshly drawn or stored at -20 degrees C for 4-6 weeks. The assays produced significantly different results for the fresh and frozen samples, however, the magnitudes of these differences were smal l, about 8% higher for the frozen samples, and independent of total ch olesterol, HDL cholesterol, triglyceride, apolipoprotein B or Lp(a) co ncentration or assay configuration. A similar difference was seen for a freshly drawn plasma sample assayed at the same time as the fresh an d frozen samples, indicating the differences were due to inherent diff erences in the assays at the times the assays were performed. The assa y configuration was an important factor in determining the Lp(a) conce ntrations for identically treated samples. ELISAs using the apoB repor ting antibody yielded concentrations that were significantly less than those determined by ELISAs using the anti-apo(a) reporting antibody. The assay differences did not correlate with total cholesterol, HDL ch olesterol, triglyceride, or apoB concentration. However, the magnitude of the difference did correlate well with Lp(a) amount. Low Lp(a) con centrations produced greater assay differences than high Lp(a) concent rations.