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Sensitive and Specific Findings

Sensitive Findings

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: or article PMID 16634744).

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Tags: Autoimmune Hematologic Tag this Diagnosis.


Population / CalculatorPrevalence Comments / Study / Link
Patients taking heparin 2% Blood 2005 Oct 15;106(8):2710-5. PMID 15985543
Heparin type 0% bovine greater risk than porcine. UFH greater risk than LMWH; fondaparinux is thought to be safest, though there are 2 case reports.
Clinical context 0% surgical patients have higher risk than medical patients.
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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 SensitivitySpecificity Comments, Study
14C-Serotonin Release Assay Edit 95%95%

"gold standard"


Platelet Aggregation Test Edit 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 SensitivitySpecificity Comments, Study
Anti-Heparin-PF4 ELISA Edit 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