4Ts Score (HIT)

4Ts Score: Used to assess the pre-test probability of Heparin-Induced Thrombocytopenia (HIT). Clinical score should be calculated before ordering HIT antibody tests.

1. Thrombocytopenia

2. Timing of Platelet Fall

3. Thrombosis or Sequelae

4. oTher Causes for Platelet Fall

Guidelines & Evidence

Verified

Last Review: 2026-07-17

When to Use

Clinical Use

Assessing the pre-test probability of Heparin-Induced Thrombocytopenia (HIT).

Deciding whether to discontinue heparin and start an alternative anticoagulant (e.g., argatroban, danaparoid).

Determining if HIT antibody testing (PF4/heparin EIA) or functional assays (SRA) are indicated.

How it Works

Criteria

Category	2 Points	1 Point	0 Points
Thrombocytopenia	>50% fall and nadir ≥20k	30-50% fall or nadir 10-19k	<30% fall or nadir <10k
Timing of fall	Days 5-10 (or <1d if recent heparin)	After Day 10 (or unclear)	≤4 days (no prior heparin)
Thrombosis	New thrombosis, skin necrosis	Progressive/recurrent thrombosis	None
oTher causes	None apparent	Possible	Definite

Clinical Pearls

Interpretation

Score	Probability	Management
0-3	Low (< 1%)	Continue heparin; do not test for HIT.
4-5	Intermediate (~10%)	Stop heparin; start alternative; test for HIT.
6-8	High (~50%)	Stop heparin; start alternative; test for HIT.

Last Comprehensive Review: 2026-07-17

In Recent Clinical News

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4Ts Score (HIT)

1. Thrombocytopenia

2. Timing of Platelet Fall

3. Thrombosis or Sequelae

4. oTher Causes for Platelet Fall

When to Use

Clinical Use

How it Works

Criteria

Clinical Pearls

Interpretation

The Evidence

Key Reference

Evaluation of pretest clinical score (4 Ts) for the diagnosis of heparin-induced thrombocytopenia

In Recent Clinical News

4Ts Score (HIT)

1. Thrombocytopenia

2. Timing of Platelet Fall

3. Thrombosis or Sequelae

4. oTher Causes for Platelet Fall

When to Use

Clinical Use

How it Works

Criteria

Clinical Pearls

Interpretation

The Evidence

Key Reference

Evaluation of pretest clinical score (4 Ts) for the diagnosis of heparin-induced thrombocytopenia

In Recent Clinical News