Abstract 13172: What is the Utility of Two Different ELISAs and the 4T's Score in Determining the Probability of Heparin-Induced Thrombocytopenia Following Cardiac Surgery?
Introduction: A platelet activation assay (eg. serotonin-release assay [SRA]), is the “gold standard” to diagnose heparin-induced thrombocytopenia (HIT); however, it is technically demanding, expensive, and not widely available. The ELISA test, to detect presence of HIT antibodies, is more readily available, but has a high false positive rate. The 4Ts score (Thrombocytopenia extent, Timing of thrombocytopenia, Thrombosis and oTher causes for thrombocytopenia) is readily available, but may be difficult to do in cardiac surgery patients who have many reasons for thrombocytopenia, may have platelet transfusions, and in whom heparin timing may be difficult to accurately determine.
Objective: To determine sensitivities (sens)/ specificities (spec) of the two different HIT ELISAs (IgG/A/M ELISA from GTI Diagnostics, and an IgG ELISA from McMaster University) and the 4Ts score in relation to the SRA.
Methods: The 4Ts score was performed on cardiac surgery patients who had the HIT ELISAs and SRA done. Receiver Operating Characteristic (ROC) curves for the tests (as compared to the gold standard SRA - positive or negative) were created to determine cut points for the tests and their sens/spec.
Results: There were 78 samples on 70 patients - 13 having a positive SRA. The area under the curve (AUC) on the ROC curve for the IgG/A/M ELISA was 0.88 (p<0.01); for IgG ELISA it was 0.93 (p<0.01); for 4Ts score it was 0.67 (p=0.10). The sens and spec of having a positive SRA with 4Ts test score of 4 or more (intermediate/high risk of HIT) was < 60% and < 65% respectively. An IgG/A/M ELISA optical density (OD) ≥1.13 was associated with a sens of 92% and spec of 72% and an IgG ELISA OD ≥ 0.99 was associated with a sens of 92% and spec of 70% as related to “gold standard” SRA.
Conclusion: The 4Ts score has less discriminatory power compared to the ELISA in cardiac surgery patients. An OD of 1.0 in either ELISA is a useful cut point to help with management decisions in regards to non-heparin anticoagulation for cardiac surgery patients.
- © 2011 by American Heart Association, Inc.