Immunoassays for heparin-induced thrombocytopenia (HIT)
There are 2 major categories of immunoassays for anti-PF4/heparin (H) antibodies (also called PF4-dependent immunoassays):
- Enzyme immunoassays (EIAs):
- High sensitivity (98–99%) for detecting pathological (platelet-activating) HIT antibodies.
- Semi-quantitative – higher optical densities predict greater likelihood of HIT.
- Lower specificity compared to functional assays such as serotonin release assay.
- Testing occurs in batches, which may delay results for 24 hours or longer.
- Latex immunoturbidimetric assay:
- Possibly higher specificity compared to EIAs.
- High sensitivity (about 98%).
- Semi-quantitative – higher result predicts greater likelihood of HIT.
- Rapid, on-demand, fully-automated laboratory assay (run on standard coagulation instrument).
- Once the sample is in the lab a result can be made available in 30 minutes or less.
In both cases, the assay detects antibodies directed against the anti-PF4/heparin complex.
Enzyme immunoassay (EIA)
Latex immunoturbidimetric assay (LIA)