Clinical Scoring, the PF4 ENHANCED Assay, and the ¹⁴ C-Serotinin Release Assay for the Diagnosis of Heparin Induced Thrombocytopenia (HIT) in Complex Medical and Surgical Patients.

BACKGROUND: Heparin-induced thrombocytopenia (HIT) is a clinico-pathological entity that presents a diagnostic challenge, especially in medically complex patients.

PATIENTS AND METHODS: In this observational and prospective study, 34 consecutive patients with suspected HIT were enrolled. They were clinically scored using two different clinical scoring systems and underwent testing for PVS-ELISA and ¹⁴C-SRA. ¹⁴C-SRA results were also available from 21 medical and surgical patients who had previously been tested.

PURPOSE: The objective of our study was to evaluate the sensitivity and specificity of the PF4 ENHANCED (GTI Diagnostics) ELISA for HIT performed at two institutions using the serotonin-release assay (¹⁴C-SRA) and clinical scoring systems as reference methods.

RESULTS: With the ¹⁴C-SRA as the reference method, the sensitivities and specificities of the ELISA were 100% and 57% respectively at one institution and 93% and 65% at the other. There was only one false-negative ELISA with the ¹⁴C-SRA as the reference standard. When compared with the clinical scoring by Greinacher et al., the sensitivity and specificity for PVS-ELISA was 81.82% and 50% and for ¹⁴C-SRA 40% and 100% respectively. Five of eleven patients who scored ’Very Likely’ by the Greinacher scoring system were either ’Unlikely’ or ’Possible’ with the Paulpard scoring system. Seven of 11patients with ’Very likely’ HIT and 7 of 8 with ’Possible’ HIT by Greinacher clinical criteria were ¹⁴C-SRA negative.

CONCLUSIONS: Our study did confirm the high specificity of ¹⁴C-SRA, however the sensitivity was low with clinical scoring as reference standard. Clinical scoring was discordant in more than 50% of patients with ’Very Likely’ HIT by Greinacher score when compared with Paulpard scoring. Thus neither the clinical score nor the ¹⁴C-SRA appears suitable as the ’gold standard’ for diagnosis of HIT. Because of its high sensitivity with the ¹⁴C-SRA as the reference method, we believe the PF4 ENHANCED ELISA should be used to identify HIT in patients with multiple potential causes of thrombocytopenia, although false-positive results will not be uncommon.