4Ts Score for Heparin-Induced Thrombocytopenia
Estimates pre-test probability of heparin-induced thrombocytopenia (HIT) to guide confirmatory testing and management
Also written as: 4Ts, 4Ts HIT, 4T score.
- Highest activation tier
- Mandatory
- How it is scored
- Scored in code; a detected disagreeing draft value is flagged for correction
- Care settings
- ICU, Inpatient
When it activates
Scribeable activates a calculator from the encounter. The 4Ts Score for Heparin-Induced Thrombocytopenia can activate when the transcript or pasted chart context documents any of these:
- Thrombocytopenia on heparin
- Platelet drop during heparin therapy
- Suspected HIT evaluation
- New thrombosis on heparin
- Heparin exposure with falling platelets
A coded diagnosis can also activate it. ICD-10 prefixes carried by the registry: D75.82, T45.515.
Note-type scope: it activates on notes whose subject resolves to hospital medicine, critical care. A note that resolves to another subject does not carry it even when the clinician's specialty matches; a note with no resolvable subject (a generic consultation) falls back to the specialty match.
Inputs the note needs
4 inputs. Each is resolved from the transcript, the pasted chart context and charted labs; an input marked "asks you" is requested as a clarification when it is undocumented.
| Input | Type | Unit / options | Guidance |
|---|---|---|---|
| Degree of platelet fall: >50% and nadir ≥20K (2), 30-50% fall or nadir 10-19K (1), <30% fall or nadir <10K (0) | lab | ||
| Timing of platelet fall: days 5-10 or ≤1 day if prior heparin within 30d (2), consistent but unclear or after day 10 (1), ≤4 days without recent exposure (0) | history | ||
| Thrombosis or other sequelae: new thrombosis, skin necrosis, or acute systemic reaction (2), progressive/recurrent or erythematous skin lesions (1), none (0) | exam | ||
| Other causes of thrombocytopenia: no other apparent cause (2), possible other cause (1), definite other cause present (0) | history |
Scoring
Four categories, each scored 0-2: Thrombocytopenia (degree of platelet fall), Timing (of platelet fall onset), Thrombosis (or other sequelae), oTher causes (of thrombocytopenia). Total range: 0-8.
Thrombocytopenia Degree of platelet fall: >50% and nadir ≥20K (2), 30-50% fall or nadir 10-19K (1), <30% fall or nadir <10K (0) + Timing Timing of platelet fall: days 5-10 or ≤1 day if prior heparin within 30d (2), consistent but unclear or after day 10 (1), ≤4 days without recent exposure (0) + Thrombosis Thrombosis or other sequelae: new thrombosis, skin necrosis, or acute systemic reaction (2), progressive/recurrent or erythematous skin lesions (1), none (0) + Other causes Other causes of thrombocytopenia: no other apparent cause (2), possible other cause (1), definite other cause present (0) (each 0-2)
Interpretation
Score 0-3: Low probability (~5% HIT). May continue heparin, HIT antibody testing optional. Score 4-5: Intermediate probability (~14-25% HIT). Send HIT antibody (ELISA or SRA), consider switching to non-heparin anticoagulant. Score 6-8: High probability (~50-80% HIT). Discontinue all heparin, start non-heparin anticoagulant (argatroban, bivalirudin, fondaparinux), send confirmatory testing. Do NOT use warfarin until platelets recover.
Evidence
Sources carried in Scribeable's citation registry for this calculator; guideline version: Lo GK et al. 2006.
- Lo GK et al. Evaluation of pretest clinical score (4T's) for the diagnosis of heparin-induced thrombocytopeniaLo et al. (4Ts HIT) 2006 · 2006 · Level I · link last verified 2026-03-28
How Scribeable handles it in the note
When an encounter activates the 4Ts Score for Heparin-Induced Thrombocytopenia at the mandatory tier, Scribeable resolves its inputs from the transcript, the pasted chart context and any charted labs, and asks you for a missing input you can supply before the note is finalised. Bedside-exam and separately ordered study values are not requested one input at a time; a calculator that carries a combined clarification question may still put that single question to you.
The score is computed in code from the resolved inputs, not recalled by the language model. If the draft states a 4Ts Score for Heparin-Induced Thrombocytopenia value that disagrees with the computed one, the disagreement is flagged to the second drafting pass, which is instructed to correct the score and its interpretation before you see the note.
Classified as a risk score: activated strictly, by a documented trigger, never by a permissive reading of the encounter.
See it activate on your own encounter
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