Abstract
BackgroundImmunoassays are crucial in the work-up of patients with suspected heparin-induced thrombocytopenia (HIT) and rapid tests have been recently developed. However, comparative data on diagnostic accuracy, reproducibility, and analytical costs of different immunoassays in clinical practice are limited.MethodsSamples of 179 consecutive patients evaluated for suspected HIT in clinical practice using a polyspecific enzyme-linked immunoabsorbent assay (GTI diagnostics; ELISA) and a rapid particle gel immunoassay (PaGIA), were additionally analysed with a IgG-specific chemiluminescent immunoassay (AcuStar HIT-IgG). Presence of HIT was defined as a positive functional heparin-induced platelet aggregation test. Diagnostic accuracy was determined for low, intermediate and high thresholds as previously established (ELISA: optical density 0.4, 1.3, and 2.0 respectively; PaGIA: positive/negative, titre of 4, titre of 32; AcuStar HIT-IgG: 1.0 U/ml, 2.8, 9.4) and reproducibility was assessed by repeated measurements. Costs of test determination were calculated taking reagents, controls, and working time of technicians according to Swiss health care system into account.ResultsData on PaGIA results were available for 171 patients (95.5%), ELISA for 144 patients (80.4%), and AcuStar HIT-IgG for 179 patients (100%). Sensitivity was above 95% for all assays at low and intermediate thresholds. Specificity increased with higher thresholds and was above 90% for all assays with intermediate and high thresholds. Specificity of AcuStar HIT-IgG (92.8%; 95% CI 87.7, 96.2) was significantly higher than PaGIA (83.0%; 95% CI 76.3, 88.5) and higher than ELISA (81.8%, 95% CI 74.2, 88.0) at low threshold (p<0.05). Reproducibility was adequate for all assays. Total costs per test were CHF 51.02 for ELISA, 117.70 for AcuStar HIT-IgG, and 83.13 for PaGIA.ConclusionsWe observed favourable diagnostic accuracy measures and a high reproducibility for PaGIA and AcuStar HIT-IgG. Implementation into 24-hours-service might improve patient care but the results must be confirmed in other settings and larger populations as well.
Highlights
The work-up of patients with suspected heparin-induced thrombocytopenia is difficult due to major practical problems and methodological restrictions [1]
Data on particle gel immunoassay (PaGIA) results were available for 171 patients (95.5%), enzyme-linked immunoassays (ELISA) for 144 patients (80.4%), and AcuStar heparin-induced thrombocytopenia (HIT)-IgG for 179 patients (100%)
A decision whether or not heparin shall be stopped and treatment with alternative anticoagulants started must be taken rapidly to prevent major complications [2]. Clinical scoring systems such as the 4Ts score are available to guide decision-making at bedside, but rating is difficult in inexperienced hands [1,3,4,5] and their positive predictive value is too low for diagnosing HIT [6,7]
Summary
The work-up of patients with suspected heparin-induced thrombocytopenia is difficult due to major practical problems and methodological restrictions [1]. A decision whether or not heparin shall be stopped and treatment with alternative anticoagulants started must be taken rapidly to prevent major complications [2] Clinical scoring systems such as the 4Ts score are available to guide decision-making at bedside, but rating is difficult in inexperienced hands [1,3,4,5] and their positive predictive value is too low for diagnosing HIT [6,7]. Functional assays such as the serotonin release assay (SRA), the heparin-induced platelet activation assay (HIPA) or the heparin-induced platelet aggregation test (PAT) are regarded as gold-standard for the diagnosis of HIT. Comparative data on diagnostic accuracy, reproducibility, and analytical costs of different immunoassays in clinical practice are limited.
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