HIT 4T Score Calculator

A clean bedside-style calculator for estimating pretest probability of heparin-induced thrombocytopenia using the 4Ts: Thrombocytopenia, Timing, Thrombosis, and oTher causes.

1. Thrombocytopenia

Select the platelet count fall that best matches the case.

2 points Platelet fall >50% and nadir ≥20 × 10⁹/L 1 point Platelet fall 30–50% or nadir 10–19 × 10⁹/L 0 points Platelet fall <30% or nadir <10 × 10⁹/L

2. Timing of platelet fall

Match the onset to recent heparin exposure.

2 points Clear onset day 5–10, or platelet fall ≤1 day with heparin exposure within past 30 days 1 point Consistent with day 5–10 but not clear, onset after day 10, or fall ≤1 day with heparin exposure 30–100 days ago 0 points Platelet fall ≤4 days without recent heparin exposure

3. Thrombosis or other sequelae

Consider new thrombosis, skin necrosis, or acute systemic reaction.

2 points New thrombosis, skin necrosis, or acute systemic reaction after IV heparin bolus 1 point Progressive/recurrent thrombosis, non-necrotizing skin lesions, or suspected thrombosis not yet proven 0 points None

4. Other causes of thrombocytopenia

Judge how likely an alternate explanation is.

2 points No other cause is evident 1 point Possible other cause is present 0 points Definite other cause is present

Calculated score

out of 8 total points

High probability

A score of 6–8 suggests a high pretest probability of HIT. Stop and think carefully before giving more heparin, and pair this with clinical judgment plus confirmatory testing pathways.

0–3: low probability
4–5: intermediate probability
6–8: high probability

This tool is for clinical support and education, not a diagnosis engine. Use local protocols, platelet trend review, heparin exposure history, and laboratory testing such as immunoassay/functional assays where appropriate.

Static deployment, so no app port is needed. That keeps it tidy and avoids stepping on anything in PORTS.md.