How is the 4Ts score interpreted?

Scores 0–3 = Low probability (HIT unlikely; testing usually unnecessary). Scores 4–5 = Intermediate probability (stop heparin, send PF4/heparin immunoassay). Scores 6–8 = High probability (stop heparin, start non-heparin anticoagulant, confirm with functional testing).

Why is the 4Ts score important?

The 4Ts score prevents over-testing and guides safe anticoagulant management. A low score has >98% negative predictive value for HIT, helping clinicians avoid unnecessary PF4 testing and therapy changes.

What are the components of the 4Ts score?

1) Thrombocytopenia: degree of platelet fall; 2) Timing: onset after heparin exposure; 3) Thrombosis: new or progressive thrombosis; 4) Other causes: presence of alternative explanations.

What actions are recommended for intermediate or high 4Ts scores?

Stop all heparin products, begin a non-heparin anticoagulant such as argatroban or fondaparinux, and send PF4/heparin immunoassay ± functional assay as per ASH 2018 guidelines.

Does the HIT Calculator replace laboratory testing?

No. The calculator provides a pretest probability estimate. Laboratory confirmation with PF4/heparin antibody testing is required for intermediate or high scores.

HIT Calculator | 4T Score for Heparin Induced Thrombocytopenia

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.

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.

Explore more Hematology calculators:

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HIT Calculator

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.

HIT Calculator 4T Score table showing thrombocytopenia, timing of platelet fall, thrombosis, and other causes with 0, 1, and 2 point scoring criteria.

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.

Flowchart for suspected heparin-induced thrombocytopenia (HIT) showing 4T score calculation, with management steps for low versus intermediate or high probability cases.

FAQs

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 out other Website Hits Calculators

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).

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.

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.

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).
Validation & interpretation of 4Ts (probability bands; negative predictive value).
Action steps for intermediate/high probability (immunoassay ± functional assays; non-heparin anticoagulants).