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4Ts score for heparin-induced thrombocytopenia

Also called 4Ts, 4 Ts score, HIT pretest probability

Pretest probability of heparin-induced thrombocytopenia from Thrombocytopenia, Timing, Thrombosis and oTher causes; a low score largely rules HIT out.

Thrombocytopenia

A >50% fall caused directly by surgery scores 1.

Timing of platelet fall
Thrombosis or other sequelae
oTher cause of thrombocytopenia

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Formula and scoring

Four items, each 0–2. Total 0–3 low, 4–5 intermediate, 6–8 high.

Exam and ward pearls

  • Its strength is ruling HIT out: the negative predictive value of a low score is high, while the positive predictive value of intermediate and high scores varied widely between centres.
  • The top thrombocytopenia score needs a nadir ≥20 ×10⁹/L; a nadir <10 ×10⁹/L scores 0 and points away from HIT.
  • Rapid fall within 1 day is possible if heparin was given in the previous 30 days.

When not to rely on it

  • Positive predictive value differed sharply between the two centres (intermediate 28.6% vs 7.9%; high 100% vs 21.4%), so intermediate and high scores need laboratory confirmation.

Source

  1. Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost. 2006;4(4):759-65. doi:10.1111/j.1538-7836.2006.01787.x · PMID 16634744

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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