False-Negative Platelet Factor 4 Antibodies and Serotonin Release Assay and the Utility of Repeat Testing in the Diagnosis of Heparin-Induced Thrombocytopenia and Thrombosis

Abstract

Objective To report a case of false-negative serological tests in the diagnosis of heparin-induced thrombocytopenia (HIT) followed by a brief review of the literature on this topic. Case Presentation A 75-year-old Caucasian female patient was admitted with a traumatic right ankle fracture that required open reduction and internal fixation. Despite postoperative subcutaneous heparin chemoprophylaxis, she developed deep vein thrombosis (DVT) and pulmonary embolism (PE) on day 4 and subsequently started on continuous heparin infusion. On day 5, she suffered a stroke from a complete occlusion of the right common carotid artery with tandem occlusion of the right middle cerebral artery. She underwent successful thrombectomy of both arteries. The proposed stroke mechanism was paradoxical embolism through a patent foramen ovale. Over the next few days, thrombocytopenia was noted, the heparin drip was stopped, and HIT antibodies (antibodies targeting the complex of platelet factor 4 and heparin; PF4-H AB) and serotonin release assay (SRA) tests were sent. Because of the suspicion for HIT, she was started on bivalirudin with subsequent improvement in platelet count. Initial PF4-H AB and SRA tests were negative, bivalirudin was stopped, and heparin was restarted. Subsequently, her platelets trended down, again raising clinical suspicion of HIT. Repeat PF4-H AB and SRA testing resulted positive. Conclusions A positive SRA in the appropriate context is considered for the diagnosis of heparin-induced thrombocytopenia. This case report highlights that false-negative serological evaluation is possible early in the course of the disease. Repeat testing is recommended in patients with high clinical suspicion.

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“…86,89 Recently, some false-negative test results have been observed for both PF4 antibodies and functional assays, thus justifying the recommendation to repeat the tests when the clinical suspicion remains very strong. 87,90 Nevertheless, perhaps the biggest problem in the identification of pathological HIT is that of "false-positives" since most antibodies identified by initial immunological testing do not lead to activation of platelets in a functional HIT assay. 69,87 Heparin-Dependent Antibodies Many immunological assays have been developed for identifying heparin-PF4 complexes and/or heparin-platelet antibodies causing HIT.…”

Heparin-Induced Thrombocytopenia in COVID-19

“…His subsequent tests (ELISA and SRA) were found to be positive. [ 30 ] All these evidences indicate a very significant role of clinical suspicion and repeated scoring by 4Ts test in all patients on heparin.…”

Using novel PF4-dependent P-selectin expression assay to diagnose heparin-induced thrombocytopaenia postliver transplantation

“…This can lead to false positive diagnoses in approximately 1 in 5 patients tested with immunoassays alone. With a higher specificity at >95%, the SRA is considered to be the gold standard in diagnosing HIT; however, case reports have found that the SRA may be falsely negative in patients who have received massive transfusions, are on immunosuppression, have low antibody titres early in the disease or have undergone multiple rounds of plasmapheresis 2 12–15. A history of cirrhotic coagulopathy may also skew diagnostic testing for HIT 12.…”