From the Guidelines
The 4T score should be used to estimate the probability of heparin-induced thrombocytopenia (HIT) in patients with suspected HIT, as recommended by the American Society of Hematology 2018 guidelines 1.
Calculation of 4T Score
To calculate the 4T score, evaluate four categories:
- Thrombocytopenia (degree of platelet count fall)
- Timing of platelet count fall
- Thrombosis or other sequelae
- Other causes of thrombocytopenia Each category is scored 0-2 points, with a maximum total score of 8.
Interpretation of 4T Score
A score of 0-3 indicates low probability of HIT (less than 5%), 4-5 indicates intermediate probability (10-50%), and 6-8 indicates high probability (greater than 50%) 1.
Management Based on 4T Score
For patients with intermediate or high probability scores, heparin should be discontinued immediately and replaced with a non-heparin anticoagulant such as argatroban, bivalirudin, or fondaparinux while awaiting confirmatory laboratory testing (typically anti-PF4/heparin antibody ELISA followed by functional assay if positive) 1. Some key points to consider when using the 4T score include:
- If there is uncertainty about the 4T score, HIT laboratory testing may be appropriate even for patients with a low-probability 4T score 1
- In patients with suspected HIT and an intermediate-probability 4T score, discontinuation of heparin is recommended, and initiation of a non-heparin anticoagulant at prophylactic or therapeutic intensity may be considered depending on the patient's risk of bleeding 1
- For patients with a high-probability 4T score and a positive immunoassay, continued avoidance of heparin and continued administration of a non-heparin anticoagulant at therapeutic intensity is recommended 1
From the Research
HIT 4T Score Overview
- The HIT 4T score is a pretest scoring system used to diagnose heparin-induced thrombocytopenia (HIT) in patients, as discussed in 2, 3, 4, 5, 6.
- The score takes into account the degree and timing of thrombocytopenia, thrombosis, and the possibility of other etiologies.
Calculation and Interpretation
- The 4T score categorizes patients into high, intermediate, or low probability of having HIT, as seen in 2, 6.
- A low 4T score has been shown to have a high negative predictive value, making it suitable for ruling out HIT in most situations, as noted in 2, 3, 4, 6.
- Patients with a low 4T score are unlikely to test positive for HIT antibodies, as demonstrated in 2, 3, 6.
Clinical Utility
- The 4T score can help reduce unnecessary HIT antibody testing and treatment, as discussed in 2, 3, 4.
- Implementing the 4T scoring system into institutional core measures can help minimize morbidity and lower healthcare costs, as suggested in 2, 3.
- The score can also guide treatment strategies using non-heparin anticoagulants and avoid unwanted thromboembolic complications, as mentioned in 4, 5.