4Ts score for heparin-induced thrombocytopenia
Pretest probability of HIT from four clinical criteria; low scores rule it out.
Switch how results are explained
Low probability of HIT (0-3). HIT is unlikely; look for another cause of thrombocytopenia and continue heparin if otherwise indicated.
- Evidence grade
- A
What it is and when to use it
The 4Ts score scores four criteria from 0 to 2 - thrombocytopenia, timing of the fall, thrombosis, and other causes - to estimate the pretest probability of HIT.
How to interpret it
0–3 is low probability, 4–5 intermediate, 6–8 high. A low score has a high negative predictive value and avoids unnecessary testing and anticoagulant changes.
Limitations and when not to use it
This is a pretest probability, not a diagnosis: an intermediate or high score must be confirmed with an immunoassay plus a functional assay. The decision to stop heparin remains clinical.
Formulas and cut-offs are from the original authors of each score; see the references.
Last reviewed: June 2026
References
- 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):759-765. PMID:16634744