Heparin Induced Thrombocytopenia: Likelihood Ratios
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
| Population / Calculator | Prevalence | 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. |
| More, Edit... | ||
The likelihood ratios of findings for Heparin Induced Thrombocytopenia are listed below. See the left navigation bar to change the display.