4Ts Score for Heparin-Induced Thrombocytopenia
What is the pretest probability of heparin-induced thrombocytopenia?
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About this tool
Four-domain clinical score guiding testing and management for suspected HIT.
Intended use
Patients with thrombocytopenia during or after heparin exposure.
Outcome
Probability of HIT
Time horizon
Current episode
Derivation population
Patients evaluated for HIT in Canadian and German centres.
Limitations
- Inter-observer variability, especially in ICU.
- Intermediate and high scores require laboratory confirmation.
Clinical problems
Evidence
Evidence level
Strong evidence
Derived and externally validated in multiple cohorts (including prospective studies) and incorporated into major clinical guidelines. Methodology
Guideline status
Recommended by the ASH 2018 guideline for management of HIT.
Discrimination
Low scores have a high negative predictive value (~99.8% in a 2012 meta-analysis).
References
- Original publicationLo GK, Juhl D, Warkentin TE, et al. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost 2006;4:759-765. Find on PubMed (opens in a new tab)
- Validation studyCuker A, Gimotty PA, Crowther MA, Warkentin TE. Predictive value of the 4Ts scoring system for heparin-induced thrombocytopenia: a systematic review and meta-analysis. Blood 2012;120:4160-4167. Find on PubMed (opens in a new tab)
- GuidelineCuker A, Arepally GM, Chong BH, et al. American Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia. Blood Adv 2018;2:3360-3392. Find on PubMed (opens in a new tab)
Version history
| Version | Formula | Effective | Reviewer | Changes |
|---|---|---|---|---|
| v1.0.0 | Lo 2006 | 2026-10-03 | — | Initial implementation with reference test vectors. |
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