4Ts Score Calculator

The 4Ts Score Calculator is a clinical assessment tool used to evaluate the probability of heparin-induced thrombocytopenia (HIT), a serious complication of heparin therapy. This calculator helps healthcare professionals assess four key criteria: Thrombocytopenia, Timing of platelet count fall, Thrombosis, and other causes of Thrombocytopenia.

What is HIT?

Heparin-induced thrombocytopenia (HIT) is a potentially serious immune-mediated adverse drug reaction to heparin therapy. There are two types:

• Type 1 HIT: Non-immunological, more common, with mild thrombocytopenia and good prognosis
• Type 2 HIT: Immunological, rare but more severe, with worse outcomes

Understanding the 4 Ts

The 4Ts scoring system evaluates four critical components:

1. Thrombocytopenia

   • Measures the magnitude of platelet count fall
   • Evaluates the platelet nadir (lowest point)

2. Timing

   • Assesses when the platelet count fall occurred relative to heparin exposure
   • Different scoring for various timing scenarios

3. Thrombosis

   • Evaluates presence of new blood clots
   • Includes skin necrosis and acute systemic reactions

4. oTher causes

   • Considers alternative explanations for thrombocytopenia

Scoring System

Each category is scored from 0 to 2 points:

Category	2 Points	1 Point	0 Points
Thrombocytopenia	>50% fall AND nadir ≥20×10⁹/L	30-50% fall OR nadir 10-19.9×10⁹/L	<30% fall OR nadir <10×10⁹/L
Timing	Clear onset between 5-10 days or ≤1 day with recent exposure	Consistent with days 5-10 but unclear or >10 days	≤4 days without recent exposure
Thrombosis	Confirmed new thrombosis or skin necrosis	Progressive/recurrent thrombosis or suspected thrombosis	None
Other Causes	None apparent	Possible	Definite

Interpreting Results

Total score interpretation:

• 6-8 points: High probability (~80%)
• 4-5 points: Intermediate probability (~14%)
• 0-3 points: Low probability (<1%)

Important Notes

• This calculator is a clinical decision support tool and should not replace professional medical judgment
• Always consult with a healthcare provider for proper diagnosis and treatment
• Laboratory confirmation may be necessary for definitive diagnosis
• Consider additional clinical factors not captured by the 4Ts score

Other Possible Causes of Thrombocytopenia

Common alternative causes include:

• Sepsis
• Recent surgery (within 72 hours)
• Bloodstream infections
• Chemotherapy/radiation (within 20 days)
• DIC (Disseminated Intravascular Coagulation)
• Drug-induced thrombocytopenia
• Immune thrombocytopenia