What is the 4Ts Score?

The 4Ts Score is a clinical scoring system for estimating the pretest probability of Heparin-Induced Thrombocytopenia (HIT), an immune-mediated thrombocytopenia caused by heparin. It assesses four categories — Thrombocytopenia, Timing, Thrombosis, and oTher causes — each worth 0, 1, or 2 points, for a total of 0–8.

How is the 4Ts Score calculated?

Select one option (0, 1, or 2 points) for each category: (1) Thrombocytopenia — the magnitude of the platelet fall and its nadir; (2) Timing — when the fall began relative to heparin exposure; (3) Thrombosis — the presence or absence of new thrombosis, skin necrosis, or a systemic reaction; (4) oTher causes — the presence or absence of another evident cause of thrombocytopenia. Add the four scores for a total of 0–8.

What do 4Ts scores of 0–3, 4–5, and 6–8 mean?

A score of 0–3 means LOW probability (HIT unlikely, high negative predictive value). A score of 4–5 means INTERMEDIATE. A score of 6–8 means HIGH probability. With an intermediate or high score, the steps commonly considered are stopping all heparin exposure and ordering PF4/heparin antibody testing — always discuss with the treating clinician.

Can this calculator diagnose HIT?

No. This calculator is an educational tool for estimating pretest probability, not for establishing a diagnosis. Diagnosing HIT requires a thorough clinical assessment and laboratory testing such as PF4/heparin immunoassay and functional assays. Always discuss the result with the doctor or clinician caring for the patient.

What are the common steps for an intermediate or high 4Ts score?

As general educational information, with intermediate or high probability the steps commonly considered are: stopping all heparin (including heparin flushes and LMWH), ordering PF4/heparin antibody testing, and considering a non-heparin anticoagulant if anticoagulation is still needed. This is not medical advice for a specific case — the decision must be made by the treating clinician.

What are the limitations of the 4Ts Score?

The 4Ts Score depends on clinical judgment for each category, so there is an element of subjectivity, especially for the oTher causes category. It is most useful when scored by a clinician who understands the patient context. It also does not replace laboratory testing and is not intended for laypeople to make their own treatment decisions.

4Ts Score Calculator — HIT Pretest Probability

The 4Ts Score estimates the pretest probability of Heparin-Induced Thrombocytopenia (HIT) from four categories — Thrombocytopenia, Timing, Thrombosis, and oTher causes — each worth 0, 1, or 2 points. The total score of 0–8 is interpreted as Low (0–3), Intermediate (4–5), or High (6–8).

⚠ Medical disclaimer: This tool is educational and not a substitute for clinical assessment. This score does not establish a HIT diagnosis. If you are a patient or a patient\u2019s family member, discuss the result with the treating doctor/clinician — do not change or stop treatment on your own.

Calculate the 4Ts Score

Select one option in each category. The score updates automatically.

Score Result

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Category	Points

Example Cases

Load an example to see each interpretation level:

Interpretation History

A brief history of calculations on this device (stored locally in your browser).

Frequently Asked Questions (FAQ)

Scope Boundary

This tool only calculates the 4Ts Score as an estimate of HIT pretest probability. It does not diagnose HIT, does not replace laboratory testing (e.g., PF4/heparin immunoassay or functional assay), and does not give treatment advice for specific cases. The oTher causes category requires clinical judgment — when in doubt, discuss with the treating clinician.

Free tool by NRTechStudio

4Ts Score Calculator — HIT Pretest Probability

Calculate the 4Ts Score

Score Result

Example Cases

Interpretation History

Frequently Asked Questions (FAQ)

Scope Boundary

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