How it's calculated
Four categories (Thrombocytopenia degree, Timing, Thrombosis/sequelae, oTher causes) are each scored 0-2, for a total of 0-8, estimating the pretest probability of heparin-induced thrombocytopenia.
Score interpretation
| Score | Probability of HIT |
|---|---|
| 0-3 | Low |
| 4-5 | Intermediate |
| 6-8 | High |
Clinical use
- A low 4Ts score has a high negative predictive value — HIT is very unlikely and heparin need not be stopped on this basis alone.
- An intermediate or high score generally warrants stopping all heparin products, starting a non-heparin anticoagulant, and sending confirmatory laboratory testing (e.g. PF4 antibody ELISA, serotonin release assay).
- The score estimates pretest probability only — it does not replace laboratory confirmation of the diagnosis.
- Applies to patients on or recently exposed to heparin (including low-molecular-weight heparin and heparin flushes) with a falling platelet count.
Frequently asked questions
What is the 4Ts Score used for?
It estimates the pretest probability of heparin-induced thrombocytopenia (HIT) in a patient with a falling platelet count on or recently exposed to heparin.
What does a low score mean?
A low score (0-3) has a high negative predictive value, making HIT unlikely — heparin does not necessarily need to be stopped on this basis alone.
What should happen with an intermediate or high score?
Heparin products are generally stopped, a non-heparin anticoagulant started, and confirmatory laboratory testing (PF4 antibody assay) sent while awaiting results.
Does the 4Ts Score confirm the diagnosis of HIT?
No — it estimates pretest probability only. Laboratory testing is needed to confirm or exclude the diagnosis.
References
- Lo GK, Juhl D, Warkentin TE, et al. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia. J Thromb Haemost. 2006;4(4):759-765.
- Cuker 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(22):3360-3392.