EFFECTS OF REPEATED FREEZE-THAW CYCLES ON ANTICARDIOLIPIN ANTIBODY IMMUNOREACTIVITY

The effect of repeated freeze-thaw cycles on anticardiolipin antibody levels was evaluated using an enzyme-linked immunosorbent assay. Norma l human serum was spiked with known quantities of freeze-dried human p olyclonal anticardiolipin antibody Ige and IgM (19 samples each) or Ig A (11 samples). Each spiked sample was split into four identical aliqu ots; one aliquot was never frozen, and the remaining three were taken through successive freeze-thaw cycles. All aliquots from each sample w ere evaluated on the same day using the same plate and reagents. A sig nificant decline in mean anticardiolipin IgG levels occurred between t he aliquot which had never been frozen and the one which had been thro ugh three freeze-thaw cycles (Student's t-test, P = .04). Although mea n IBM and IgA values declined as well, the differences were not signif icant. When individual samples were evaluated the decline appeared to occur most often between the second and third freeze-thaw cycle. Eight anticardiolipin IgG and three IgM-containing samples which had been p ositive initially became negative by the third freeze-thaw cycle. Thes e data show that handling and storage of serum used to perform anticar diolipin antibody assays are important potential sources of assay vari ability.