A clinical-laboratory algorithm incorporating optical density value to predict heparin-induced thrombocytopenia

The diagnosis of heparin-induced thrombocytopenia (HIT) is complex and involves integrating both clinical and laboratory findings. Readily available diagnostic tests such as the heparin-dependant antibody assay (HDAA) lack desired specificity when utilised alone. A diagnostic algorithm incorporating the 4T pretest probability score, HDAA, and optical density (OD) value was implemented as a tool to assist in the diagnosis of HIT and with the decision to treat patients. Patients with a 4T score >3 and/or positive HDAA result with an OD ≥1 were considered positive. Utilisation of this algorithm was hypothesised to improve the identification of patients without SRA confirmed HIT and improve overall specificity compared to other diagnostic strategies. Retrospective chart review was conducted and included patients with a positive or equivocal HDAA result and a serotonin release assay result during a two-year period. Each patient was evaluated for the diagnosis of HIT using the algorithm. The specificity and sensitivity of the diagnostic algorithm to identify subjects with SRA confirmed HIT was evaluated. A total of 83 patients were identified for inclusion in the study. The diagnostic algorithm identified 22 patients for direct thrombin inhibitor (DTI) therapy. Nine of these patients were SRA positive. The sensitivity of the algorithm was 0.9 with a specificity of 0.822. The diagnostic algorithm was found to be both more specific and sensitive than other diagnostic strategies including the 4T score alone, HDAA alone, and the combination of the 4T score and HDAA results. This preliminary data suggest a diagnostic algorithm combining 4T score, HDAA, and OD value may be a tool to aid in the identification SRA positive patients for DTI therapy.