Rapid immunoassays for diagnosis of heparin-induced thrombocytopenia: comparison of diagnostic accuracy, reproducibility, and costs in clinical practice
A. Bankova1, Y. Andres2, M. Horn3, L. Alberio4, M. Nagler3 (1Lucerne, Switzerland, 2Muri, Switzerland, 3Bern, Switzerland, 4Lausanne, Switzerland)
Time: 17:15 - 18:15
Objective: Immunoassays are crucial in the work-up of patients with suspected heparin-induced thrombocytopenia (HIT) and a number of rapid tests have been recently developed. However, comparative data on diagnostic accuracy, reproducibility, and analytical costs of different immunoassays in clinical practice are limited.
Methods: Samples of 187 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 analyzed with two fully automatable assays: polyspecific chemiluminescent immunoassay (HIT-Ab), and IgG-specific chemiluminescent immunoassay (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 2, titre of 4; HIT-Ab/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.
Results: Data on PaGIA results were available for 177 patients (94.7%), ELISA for 146 patients (78.1%), HIT-Ab for 54 patients (28.9%), and HIT-IgG for 187 patients (100%). Sensitivity was 100% 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 HIT-IgG was higher than PaGIA at all thresholds and higher than ELISA at low threshold. Reproducibility was adequate for all assays. Total costs per test were CHF 51.02 for ELISA, 117.70 for HIT-Ab and HIT-IgG, and 83.13 for PaGIA.
Conclusion: In clinical practice, we observed favourable diagnostic accuracy measures and a high reproducibility for rapid immunoassays PaGIA and chemiluminescent immunoassays. Implementation into 24-hours-service might improve patient care.