Correlation of ELISA Optic Density with Clinical Diagnosis of Heparin-Induced Thrombocytopenia: A Retrospective Study of 104 Patients with Positive Anti-PF4/Heparin Antibodies

• Published in: Blood 2012-11, Vol.120 (21), p.2242-2242
• Main Authors: Pearson, Marc-Andre, Blais, Normand
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V120.21.2242.2242

Abstract 2242 Heparin-induced thrombocytopenia (HIT), which is characterized by thrombotic events, is a serious complication of heparin use. Its diagnosis is primarily clinical but can be supported by several laboratory tests. ELISA for anti-PF4/heparin antibodies, which is the most widely-available technique, is expressed in terms of optical density (OD) results. This test was shown to have good sensitivity but poor positive predictive value. The goal of this study is to correlate OD levels with the probability of HIT diagnosis. Contrarily to previous studies where the diagnosis of HIT was mainly based on laboratory findings, we have defined HIT based on the strength of the original diagnosis, the retrospective adjudication performed by one or two clinicians familiar with HIT diagnosis, the absence of thrombosis and the absence of a clearly identified alternative diagnosis for the thrombocytopenia. We conducted a retrospective study involving 104 patients with a positive ELISA for anti-PF4/heparin antibodies (Stago Asserachrom HPIA essay) between 2008 and May 2012. For all patients who were hospitalized at the CHUM, an extensive chart review was performed from the day of admission and for a period of 3 months following the positive ELISA assay. For each patient that was included in the study, the Greinacher clinical score was calculated. According to the clinical evolution and the laboratory results, a final, clinical, retrospective diagnosis was made for each patient (which was either HIT-positive or HIT-negative). The OD result was collected only after diagnosis was made. In our study, 28.8% of the patients were HIT-positive and 71.2% HIT-negative. There was a statistically significant difference in ELISA results between these two groups (Figure 1). Mean OD was 0.83 (SD ± 0.62) for HIT-negative patients, versus 2.15 (SD ± 0.76) for HIT-positive ones (P< 0.001). Figure 2 shows a distribution of patients according to Greinacher score and final diagnosis. In patients with low clinical probability, HIT-positive patients had statistically higher mean OD than HIT-negative patients (3.0 ± 0.14 versus 0.66 ± 0.36, P