🩸 4Ts Score (Heparin-Induced Thrombocytopenia)
UseEstimate the pretest probability of HIT.
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SourceLo GK, et al. J Thromb Haemost 2006
Runs locally in your browser (no PHI uploaded). For licensed clinicians — not a substitute for clinical judgement.
Stored on this device for revisit reminders
This-shift next steps
After scoring: open the scene pack, peer scores, and the matching pathway. Local reference — no HIS write.
Score + version; reference only — not a substitute for care · no HIS write
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Methodology · worked example, guidelines & full notes
Clinical takeaway
Low score (0–3) has a high negative predictive value — HIT is unlikely.
When to use
Estimate the pretest probability of HIT.
How it works
Four domains (Thrombocytopenia, Timing, Thrombosis, oTher cause) each 0–2. 0–3 low, 4–5 intermediate, 6–8 high probability.
Key points
- Low score (0–3) has a high negative predictive value — HIT is unlikely.
- Intermediate/high scores warrant stopping heparin and immunoassay/functional testing.
- Do not wait for testing to switch anticoagulant if probability is high.
References
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Thrombocytopenia | Fall 30–50% or nadir 10–19 (1) |
|---|---|
| Timing of platelet fall | Consistent but unclear, or after day 10 (1) |
| Thrombosis or sequelae | Progressive/recurrent or erythematous lesions (1) |
| Other cause of thrombocytopenia | Possible (1) |
→4Ts4/8
- Probability：Intermediate probability
- Action：A low score has a high negative predictive value; the positive predictive value of intermediate and high scores varies by setting, and diagnosis relies on antibody and functional assays.
| Thrombocytopenia | Fall > 50% & nadir ≥ 20 (2) |
|---|---|
| Timing of platelet fall | Day 5–10, or ≤ 1 day with recent heparin (2) |
| Thrombosis or sequelae | New thrombosis or skin necrosis (2) |
| Other cause of thrombocytopenia | None apparent (2) |
→4Ts8/8
- Probability：High probability
- Action：A low score has a high negative predictive value; the positive predictive value of intermediate and high scores varies by setting, and diagnosis relies on antibody and functional assays.
Verification & sources · governance
FAQ
Frequently asked questions
- What are the limits and cautions when using 4Ts Score (Heparin-Induced Thrombocytopenia)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- Does 4Ts Score (Heparin-Induced Thrombocytopenia) upload patient data? Where is it calculated?
- Calculation runs locally in the browser; inputs and results are not uploaded. For licensed clinicians only; interpret with history, investigations and local protocols — not a diagnosis or prescription.
- How is 4Ts Score (Heparin-Induced Thrombocytopenia) calculated in practice? Can you show a worked example?
- Inputs: Thrombocytopenia Fall 30–50% or nadir 10–19 (1), Timing of platelet fall Consistent but unclear, or after day 10 (1), Thrombosis or sequelae Progressive/recurrent or erythematous lesions (1), Other cause of thrombocytopenia Possible (1) → Result: 4Ts 4 /8（Probability: Intermediate probability, Action: A low score has a high negative predictive value; the positive predictive value of intermediate and high scores varies by setting, and diagnosis relies on antibody and functional assays.） Inputs: Thrombocytopenia Fall > 50% & nadir ≥ 20 (2), Timing of platelet fall Day 5–10, or ≤ 1 day with recent heparin (2), Thrombosis or sequelae New thrombosis or skin necrosis (2), Other cause of thrombocytopenia None apparent (2) → Result: 4Ts 8 /8（Probability: High probability, Action: A low score has a high negative predictive value; the positive predictive value of intermediate and high scores varies by setting, and diagnosis relies on antibody and functional assays.）