What is the predictive accuracy of the 4Ts core for heparin-induced thrombocytopenia (HIT)?

Updated: Sep 10, 2021
  • Author: Sancar Eke, MD, FASN; Chief Editor: Srikanth Nagalla, MD, MS, FACP  more...
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A systematic review and meta-analysis by Cuker and colleagues found that a low-probability 4Ts score was a robust means of excluding HIT, with a negative predictive value of 0.998 (95% confidence interval [CI], 0.970-1.000). These researchers proposed that in patients with a low-probability 4Ts score, it may be possible to exclude HIT without further laboratory testing and continue heparin. [42]

Cuker and colleagues reported that the positive predictive value of an intermediate 4Ts score was 0.14 (95% CI, 0.09-0.22) and that of a high-probability score was 0.64 (95% CI, 0.40-0.82). [42] In other studies, the 4Ts model has demonstrated a positive predictive value of 9%–17%. [45]

Overdiagnosis of HIT in surgical patients with critical illness has been reported. [46] A retrospective study in surgical intensive care unit patients by Berry and colleagues found that 8.6 % of patients with low-probability 4Ts scores were positive for HIT on laboratory testing, and 57% of patients with high-probability scores of 6-8 were HIT negative. These researchers concluded that testing or treatment for HIT should not depend on the 4Ts score alone. [47]

HIT expert probability score

The HIT expert probability score (HEP) is a more detailed system developed to improve on the diagnostic utility of the 4Ts score. Testing in a validation cohort showed that the HEP model was 100% sensitive and 60% specific for determining the presence of HIT, and demonstrated better correlation with serologic HIT testing and better interobserver agreement than the 4Ts score. Nevertheless, the researchers cautioned that prospective multicenter validation is warranted.

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