4Ts Score (Heparin-Induced Thrombocytopenia)
Scores the 4Ts pretest probability of heparin-induced thrombocytopenia over four domains of 0 to 2 points.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Thrombocytopenia, 0 to 2
- 2
- Timing of the platelet fall, 0 to 2
- 2
- Thrombosis or other sequelae, 0 to 2
- 2
- Other causes of thrombocytopenia, 0 to 2
- 2
Result: 4Ts score 8 of 8
The tool opens with these values already filled in. Replace them with your own.
What the result means
- 6 to 8
- High probability. Send an immunoassay and consider stopping heparin empirically. A high score is a reason to test, not a diagnosis.
- 4 to 5
- Intermediate probability. An immunoassay is recommended.
- 3 or below
- Low probability. Laboratory testing is recommended AGAINST - the negative predictive value of a low score is near total.
- Thrombocytopenia
- 2 for a fall over 50 percent with a nadir at or above 20; 1 for a fall of 30 to 50 percent or a nadir of 10 to 19; 0 below that.
- Timing
- 2 for a clear onset between DAYS 5 AND 14, or a fall within 1 day with exposure in the past 30 days. Not the narrower 5 to 10 window still widely quoted.
- Thrombosis
- 2 for new confirmed thrombosis, skin necrosis at injection sites, an anaphylactoid reaction after an IV bolus, or adrenal hemorrhage; 1 for progressive or suspected events.
- Other causes
- 2 when none is apparent, 1 when one is possible, 0 when one is definite.
- Missing data
- Where key information is missing, err on the side of a HIGHER score rather than scoring absent data as zero - and testing may be appropriate despite a low score.
What you enter
- Thrombocytopenia, 0 to 2
- Timing of the platelet fall, 0 to 2
- Thrombosis or other sequelae, 0 to 2
- Other causes of thrombocytopenia, 0 to 2
- Key information is missing
How this is calculated
Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A. Evaluation of pretest clinical score (4 Ts) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost. 2006;4(4):759-765, as published by the American Society of Hematology. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.