Hammerer-Lercher, Angelika; Nilius, Henning; Studt, Jan-Dirk; Tsakiris, Dimitrios A; Greinacher, Andreas; Mendez, Adriana; Schmidt, Adrian; Wuillemin, Walter A; Gerber, Bernhard; Kremer Hovinga, Johanna A; Vishnu, Prakash; Graf, Lukas; Bakchoul, Tamam; Nagler, Michael (2023). Limited concordance of heparin/PF4 antibody assays for the diagnosis of heparin-induced thrombocytopenia: an analysis of the TORADI-HIT study. Journal of thrombosis and haemostasis, 21(9), pp. 2559-2568. Wiley-Blackwell 10.1016/j.jtha.2023.05.016
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BACKGROUND
Anecdotal reports suggest that the correlation between heparin/PF4 antibody assays for the diagnosis of heparin-induced thrombocytopenia (HIT) is limited. To address this issue, we investigated the correlation between widely used assays and examined possible factors contributing to variability.
METHODS
This is a large, prospective cohort study with 10 participating tertiary care hospitals including 1'393 patients with suspected HIT in clinical practice. HIT was defined by a positive heparin-induced platelet activation assay (HIPA; washed-platelet reference standard test). Three different immunoassays were used to measure heparin/PF4 antibodies: chemiluminescent immunoassay (CLIA), enzyme-linked immunosorbent assay (ELISA), and particle gel immunoassay (PaGIA). Various factors that could influence the assays were examined: sex (male, female), age (< 65 years, ≥ 65 years), unfractionated heparin exposure, presence of thrombosis, cardiovascular surgery, and intensive care unit. Spearman's correlation coefficients were calculated. Z-scores, and diagnostic odds ratios (DOR) were determined in above-mentioned subgroups of patients.
RESULTS
Among 1,393 patients, 119 were classified as HIT positive (prevalence 8.5%). The median 4Ts score was 5 in patients with HIT (interquartile range, IQR, 4-6), compared to 3 in patients without (IQR 2-4). Correlations (rs) between immunoassays were weak (0.53 to 0.65). Inconsistencies between immunoassays could not be explained by further analyses of z-scored test results and DOR in subgroups of patients.
CONCLUSIONS
The correlation between widely used heparin/PF4 antibody assays was weak and key factors could not explain this variability. Standardization of immunoassays is requested to improve comparability.
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