PURPOSE: Prompt diagnosis remains crucial in the management of heparin-induced thrombocytopenia (HIT). There are several clinical scoring tools for determining the likelihood of HIT, but these rubrics have not been prospectively validated.
METHODS: We prospectively evaluated two clinical scoring tools. We calculated in consecutive patients undergoing HIT antibody testing (and while blinded to final diagnosis for thrombocytopenia) both the 4Ts & Chong scores. Raw 4T scores were segregated into risk class groups: low likelihood (score 0-3), intermediate (4-5), and high (>5). The Chong score was also segregated into class groups: unlikely (<3), possible (3-4), probable (5-6), and definite (>6). Both class groups were further dichotomized to low risk (low likelihood for 4Ts; unlikely for Chong) and high risk (all else). We compared the prevalence of HIT antibodies (measured by EIA) and positive serotonin release assays (SRA) in the cohort. A positive SRA represented the gold standard for the diagnosis of HIT.
RESULTS: The cohort included 100 subjects (mean age: 64.0+/-16.2; male: 53%). The mean 4T score was 2.3+/-1.4 and the mean Chong score was 1.8+/-1.5. HIT antibodies were present in 14.0% and SRAs were positive in 2.0%. The prevalence of HIT antibody positivity increased with increasing 4Ts class (9.5% low, 35.7% intermediate, and 50% high; p=0.011). The same was seen with the Chong score (HIT+: 1.4% unlikely, 35.3% possible, 66.7% probable, 100% definite; p<0.0001). Based on SRA findings, the negative predictive value (NPV) of being low risk with the 4Ts and Chong scores were 98.8% and 100%, respectively. As a screening tool for HIT, the 4T class group had an area under the receiver operating characteristic (AUROC) curve of 0.66 (95% CI, 0.49-0.83) and the Chong score had an AUROC of 0.92 (95% CI, 0.821-1.000).
CONCLUSION: The NPV of the 4Ts and Chong score are high.
CLINICAL IMPLICATIONS: The 4Ts and Chong scores can accurately rule out the diagnosis of HIT when risk class is low and preclude the need for further serologic evaluation for HIT.
DISCLOSURE: Chee Chan, Grant monies (from industry related sources) This research project was funded through a research grant by Glaxo Smith Kline (GSK).; No Product/Research Disclosure Information