4Ts Score

Pre-test probability of heparin-induced thrombocytopenia (HIT)

Thrombocytopenia

0 — Platelet fall < 30% or nadir < 10 ×10⁹/L

1 — Fall 30–50% or nadir 10–19 ×10⁹/L

2 — Fall > 50% and nadir ≥ 20 ×10⁹/L

Timing of platelet count fall

0 — Fall < 4 days without recent heparin exposure

1 — Consistent with days 5–10 but unclear, onset after day 10, or ≤ 1 day with heparin in the past 30–100 days

2 — Clear onset days 5–10, or ≤ 1 day with heparin in the past 30 days

Thrombosis or other sequelae

0 — None

1 — Progressive / recurrent thrombosis, non-necrotising skin lesions, or suspected but unproven thrombosis

2 — New thrombosis, skin necrosis, or acute systemic reaction after an IV heparin bolus

Other cause of thrombocytopenia

0 — Definite other cause present

1 — Possible other cause

2 — No other cause apparent

Evidence

Original publication

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 management studies. A low score (0–3) had a negative predictive value near 100% for HIT; intermediate (4–5) and high (6–8) scores carried progressively higher probability.

Journal of Thrombosis and Haemostasis, 2006

Open source

Validation

Cuker A, Gimotty PA, Crowther MA, Warkentin TE. Predictive value of the 4Ts scoring system for heparin-induced thrombocytopenia: a systematic review and meta-analysis. Pooled negative predictive value of a low score was 0.998, supporting its use to exclude HIT.

Blood, 2012

Open source

Guideline

The 2018 ASH guidelines on the management of HIT recommend the 4Ts score to stratify pretest probability, reserving immunoassays and functional testing for intermediate- or high-probability patients.

Last reviewed: 2026-09

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