Heparin‐induced thrombocytopenia in end‐stage renal disease: Reliability of the PF4‐heparin ELISA

BACKGROUND: Diagnosing heparin‐induced thrombocytopenia (HIT) in patients with end‐stage renal disease (ESRD) can be difficult, as they are frequently exposed to heparin and have multiple etiologies for thrombocytopenia. OBJECTIVE: To correlate 4T scores, IgG heparin–platelet factor 4 (PF4‐heparin) ELISA results, and serotonin release assay (SRA) results in patients with ESRD. METHODS: We performed a retrospective review of patients with ESRD (creatinine clearance < 15 mL/min or on renal replacement therapy [RRT]) who underwent PF4‐heparin ELISA testing from October 2015 to September 2019. True‐positive PF4s required an intermediate to high 4T score (≥4), a positive SRA, and receipt of treatment for a HIT diagnosis. False‐positive PF4s were defined as a positive PF4 with a negative SRA, low 4T score (<4), or lack of treatment for HIT. Indeterminant cases were classified on the basis of clinical assessment by the treating team (eg, hematology or vascular medicine). RESULTS: Of 254 patients with ESRD (92% on RRT), 29 patients (11.4%) had a positive PF4. Eleven (37.9%) had a confirmed diagnosis of HIT: 10 patients who met all of the above criteria, and one who met the 4T criteria and was treated for HIT but did not have SRA testing due to high clinical suspicion and a positive PF4 test. False‐positive PF4 values occurred in 8 patients (27.5%). Of 10 (34.5%) indeterminant cases of patients with a negative SRA but intermediate to high 4T and positive PF4, only 3 patients were treated for HIT, whereas the other 7 were judged not to have HIT as assessed by the treating clinician. In patients with an intermediate to high 4T score and PF4 optical density > 0.4 but negative SRA, who were not treated for HIT, there were no adverse outcomes documented such as new or progressive thrombosis. CONCLUSION: In our ESRD population, 4T scores and PF4 testing were not predictive of a clinical diagnosis of HIT.