Table 1. Diagnostic sensitivity of various laboratory tests for anti-PF4 disorders.
| cHIT | aHIT | SpHIT | VITT | |
|---|---|---|---|---|
| PF4/polyanion-EIA | >99% | >99% | >99% | >99% |
| Rapid immunoassay a | >95% | >95% | >80% b | <25% |
| PAA (washed): heparin | >95% | >95% c | >80% b | ∼50% d |
| PAA (washed): PF4 | >95% | >95% | >95% b | >95% |
Abbreviations: aHIT, autoimmune heparin-induced thrombocytopenia; cHIT, classic heparin-induced thrombocytopenia; EIA, enzyme immunoassay; PAA, platelet activation assay (e.g., serotonin-release assay [SRA], heparin-induced platelet activation [HIPA] test); PF4, platelet factor 4; RIA, rapid immunoassay; SpHIT, spontaneous HIT; VITT, vaccine-induced immune thrombotic thrombocytopenia.
Note: Diagnostic specificity depends on the clinical context, but, in general, specificity is highest for the PAAs and lowest for the EIAs.
Rapid immunoassays include chemiluminescence immunoassay, latex immunoturbidimetric assay, lateral flow immunoassay, and particle gel assay.
Very rough estimate (given the paucity of cases of SpHIT reported in the literature).
Platelet activation can be seen even in the absence of adding heparin.
Estimated frequency based on any positive reaction at 0, 0.1, or 0.3 U/mL heparin (without regard to whether there is enhanced or inhibited reactivity in the presence of heparin).