Heparin Induced Thrombocytopenia: Sensitivity and Specificity

Introduction: Also known as HITT (heparin induced thrombocytopenic thrombosis) because of its predilection for causing thromboses. Note that these can be arterial or venous, though DVT is most common.

Occurs 5-14 days after exposure, unless patient has been exposed to heparin in the preceeding 100 days (in which case it can present earlier than 4 days). Platelet nadir is ~50k, i.e. not as low as for drug-induced immune related thrombocytopenias.

Must treat with a DTI in addition to stopping heparin. Do NOT use coumadin as this can lead to increased thrombosis.

A pretest probability score-based system has been validated (see table in UpToDate: http://www.utdol.com/online/content/topic.do?topicKey=coagulat/8950 or article PMID 16634744).

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Prevalence

The sensitivity and specificity of findings for Heparin Induced Thrombocytopenia are listed below. See the left navigation bar to change the display.

Sensitive and Specific Findings

Finding	Sensitivity	Specificity	Comments, Study
14C-Serotonin Release Assay	95%	95%	"gold standard" Study: http://www.utdol.com/online/content/topic.do?topicKey=coagulat/8950
Platelet Aggregation Test	90%	90%	generally thought of as more specific than sensitive, though different numbers are reported depending on the study. Study: N Engl J Med. 2006 Aug 24;355(8):809-17. PMID: 16928996 and Thromb Haemost 1993 Apr 1;69(4):344-50. PMID 8497847

Sensitive Findings

Finding	Sensitivity	Specificity	Comments, Study
Anti-Heparin-PF4 ELISA	97%	80%	false positives are caused by IgM antibodies that do not cause HIT but do react positively on the ELISA. Study: N Engl J Med. 2006 Aug 24;355(8):809-17. PMID: 16928996