Heparin-Induced Thrombocytopenia (HIT) Assays

HIT refers to thrombocytopenia that develops during or following the administration of heparin. There are various assays in use, none entirely satisfactory.

There are two groups of assays:

Immunologic: ELISA assays: use specific IgG antibodies; these assays have a high negative and positive predictive value.

Functional: Serotonin release assay, the gold standard for diagnosing HIT. An alternative functional assay is platelet aggregation standardized to use heparin as the aggregating agent.

Normal values

ELISA: negative if <0.4 optical density

Serotonin release assay (depends on the laboratorys own methodology): negative or positive

Use

An HIT assay should be performed whenever HIT is clinically suspected.

Limitations

ELISA requires well-trained, experienced technologists for accurate performance.

Serotonin release requires the use of radioactive materials. It is performed in only a few reference laboratories.