Screening and Diagnosis Laboratory Diagnosis
Assays Can Be Divided Into Two Major Categories According to the End Point They Measure
ÎAntigen assays, the most commonly used being enzyme-linked immunosorbent assays (ELISA), that detect the presence of HIT antibodies are very sensitive but only moderately specific. ELISAs that detect only IgG antibodies appear to have better specificity for HIT.
ÎFunctional assays, such as the serotonin release assay (SRA) and heparin- induced platelet activation (HIPA), that detect evidence of platelet activation (by HIT antibodies) in the presence of heparin are sensitive and specific for HIT because they detect only antibodies that are capable of activating platelets.
Comment: Unfortunately, they are available only at a few centers because they are technically difficult, require human platelets from known reactive donors, and in the case of the SRA, require working with radiation.
Figure 1. Screening for HIT
heparin or LMWH for ≥ 5 days
Patients receiving
Risk < 1%
Risk ≥ 1%
platelet count unnecessary
Monitoring
every 2-3 days for days 4-14 (or until heparin is stopped, whichever occurs first)
Monitor platelet count
