Use this hit calculator (4Ts scoring system) to estimate the pretest probability of heparin-induced thrombocytopenia (HIT) in patients exposed to heparin. Enter the four “T’s” below and get an instant score with risk category and next-step guidance (per ASH 2018 recommendations).
Clinical note: Low 4Ts (0–3) → HIT is unlikely; consider not ordering HIT testing. Intermediate (4–5) or High (6–8) → stop heparin, consider a non-heparin anticoagulant, and send PF4/heparin immunoassay ± functional testing.
4Ts Score — HIT Calculator
Total 4Ts: 0 / 8
Risk: —
This tool supports, not replaces, clinical judgment.Sources
- American Society of Hematology (ASH) Pocket Guide: Diagnosis & Management of HIT (2018)
- ASH Clinical Practice Guideline (full text): Blood Advances. 2018;2(22):3360–3392
- Original 4Ts development: Lo et al. J Thromb Haemost. 2006
- 4Ts meta-analysis (NPV of low 4Ts): Cuker et al. Blood. 2012
Medical Disclaimer
This HIT calculator is provided for educational purposes for trained clinicians. It does not constitute medical advice and does not replace clinical judgment, institutional protocols, or consultation with a hematology specialist. Do not start, stop, or change any anticoagulant or other medication based solely on this calculator. If this is an emergency, call your local emergency number.
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What is the HIT Calculator?
This hit calculator implements the 4Ts score to estimate the pretest probability of HIT in patients exposed to heparin. Each of the four domains—Thrombocytopenia, Timing, Thrombosis, and Other causes—is scored 0–2, for a total of 0–8. Categories: Low (0–3), Intermediate (4–5), High (6–8) probability.
Why the 4Ts score matters
A low 4Ts score has a very high negative predictive value and usually rules out HIT—helping avoid unnecessary, costly tests. Intermediate/high scores prompt stopping heparin, starting a non-heparin anticoagulant, and sending PF4/heparin immunoassay with functional testing as indicated.
Interpretation at a glance
- 0–3 (Low): HIT unlikely; usually avoid HIT testing.
- 4–5 (Intermediate): Stop heparin, send immunoassay; consider non-heparin anticoagulant; confirm with functional assay.
- 6–8 (High): Stop heparin, start non-heparin anticoagulant; confirmatory testing.
Disclaimer: Educational tool only. Always use clinical judgment; follow institutional protocols.
FAQs
Q1: Is a hit calculator the same as a website hits calculator?
No. This page’s HIT calculator is a medical tool for heparin-induced thrombocytopenia. A website hits calculator estimates web traffic/visits and is unrelated to medicine. If you’re looking for web analytics, check our Website Hits Calculator (create a separate page/slug later and interlink from here).
Q2: What does the 4Ts “hit calculator” measure?
It sums 4 items—Thrombocytopenia, Timing, Thrombosis, Other causes—to predict HIT probability (Low 0–3; Intermediate 4–5; High 6–8).
Q3: Are “hit points calculator”, “calculate hit points”, or “hit point calculator” related to this?
Those are gaming terms (e.g., “hit points” in RPGs) and not related to the medical HIT calculator. We include these terms here only to clarify the difference for users who land on the wrong topic.
Q4: When should clinicians act on a high 4Ts score?
With intermediate/high scores, stop heparin, consider non-heparin anticoagulation, and send PF4/heparin immunoassay ± functional testing per ASH.
Q5: Does the hit calculator replace lab tests?
No. It guides pretest probability. Testing strategy depends on the risk category and clinical context.
Sources
- ASH 2018 Guidelines / Pocket Guide for HIT (4Ts use, thresholds, and management flow). American Society of Hematology
- Validation & interpretation of 4Ts (probability bands; negative predictive value). PubMed Central
- Action steps for intermediate/high probability (immunoassay ± functional assays; non-heparin anticoagulants). American Society of Hematology