Comparison of Washed Platelet and cPRP Activation Assays

It became evident during the mid-1980s that the sensitivity of c-PRP aggregation assays for HIT was relatively poor (Kelton et al., 1984; Pfueller and David, 1986). Favaloro and colleagues (1992) first compared the c-PRP aggregation assay with the washed platelet SRA. They observed that only 6 of 13 HIT sera or plasmas that tested positive in the SRA also tested positive in the c-PRP aggregation assay. In contrast, no sample was identified that tested positive only in the aggregation assay. Chong and colleagues (1993a) also found a higher sensitivity for the SRA method. However, considerable variability in sensitivity for HIT antibodies among the various platelet donors was seen, ranging from 39-81% (c-PRP assay) to 6594% (washed platelet SRA).

Strong evidence in favor of a higher sensitivity for washed platelet assays was provided by direct comparison using platelets prepared and tested in parallel that were obtained simultaneously from the same platelet donors (Greinacher et al., 1994a). Only 23 of 70 HIT sera that tested positive by the HIPA assay also tested positive using c-PRP aggregation. In contrast, all but one of 24 sera testing positive in the c-PRP aggregation assay also tested positive in the HIPA test.

More recently, Walenga and colleagues (1999) also found a lower sensitivity of the c-PRP aggregation test compared with the SRA. In contrast, Pouplard et al. (1999) reported a similarly high sensitivity of the c-PRP as the SRA (91% vs. 88%), but with a lower specificity (77% vs. 100%).

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