Is a Negative ELISA HIT Really Negative?
Joann Lohr1, Emily Wright2, Kurt Leuenberger2, Jay Jiang2.
1Lohr Surgical Specialists, Cincinnati, OH, USA, 2Mercy West, Cincinnati, OH, USA.
OBJECTIVE- To increase awareness that a negative ELISA test may represent a false negative result. Serotonin assays are confirmatory but are no longer being routinely done in order to contain costs. This practice needs to be carefully considered especially when platelet counts remain low. We describe a case of heparin induced thrombocytopenia in a patient with a negative ELISA test.
METHODS - Case report and retrospective review of literature of heparin and HIT antibodies and testing.
RESULTS- The patient is a 58 year old male who underwent aortic prosthetic valve replacement and aortic reconstruction. His hospital course was complicated by bowel perforation and subtotal colectomy seven days post-op. All labs were consistent with his hospital course at that time. Ten days later while the patient was on a heparin drip, he developed a persistent decline in platelet count. At this point, an ELISA test was negative. Further testing, four days later included a serotonin release assay which came back positive for heparin induced thrombocytopenia (HIT). He was treated with Argatroban.
CONCLUSIONS: In a patient population where anticoagulation is imperative, when should we be suspicious of false negatives? The multitude of tests for heparin induced thrombocytopenia have varying degrees of sensitivity and specificity. Providers must be aware that false negatives can and do occur with both platelet aggregation studies and ELISA antibody tests. In a patient who is not recovering as expected, there must be suspicion for heparin induced thrombocytopenia and the most definitive test, the serotonin release assay, must be performed. In some circumstances where there is a high degree of suspicion for HIT, it may be beneficial to bypass initial ELISA or platelet aggregation screening tests in favor of the serotonin release assay which will have the best chance of catching patients who may otherwise not be discovered. Treatment and testing should be tailored to the clinical situation.
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