Heparin‐induced thrombocytopenia: towards standardization of platelet factor 4/heparin antigen tests

• Published in: Journal of thrombosis and haemostasis Vol. 8; no. 9; pp. 2025 - 2031
• Main Authors: GREINACHER, A., ITTERMANN, T., BAGEMÜHL, J., ALTHAUS, K., FÜRLL, B., SELLENG, S., LUBENOW, N., SCHELLONG, S., SHEPPARD, J. I., WARKENTIN, T.E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-09-2010
• Subjects: Adult; Aged; Female; heparin; Heparin - adverse effects; Heparin - chemistry; Heparin - pharmacology; heparin‐induced thrombocytopenia; Humans; Immunoenzyme Techniques - methods; Immunoglobulin G - chemistry; laboratory testing; Male; Middle Aged; Platelet Factor 4 - chemistry; platelets; Reference Values; Regression Analysis; Reproducibility of Results; Risk; Serotonin - chemistry; Sex Factors; Thrombocytopenia - metabolism
• ISSN: 1538-7933; 1538-7836; 1538-7836
• DOI: 10.1111/j.1538-7836.2010.03974.x

Background: Laboratory confirmation of heparin‐induced thrombocytopenia (HIT) is based on detection of heparin‐dependent platelet‐activating antibodies. Platelet factor 4 (PF4)/heparin enzyme‐immunoassays (EIA) are a widely available surrogate for platelet‐activating antibodies. Objective: Defining the optical density (OD) reactivity profiles of a PF4/heparin EIA in reference subject and patient populations and the correlation of the EIA results (expressed in OD units) with the prevalence of platelet‐activating antibodies. Patients/methods: Using quantile regression we determined the 97.5th percentile of PF4/heparin‐immunoglobulin G (IgG) EIA reactivities in non‐heparin‐treated individuals [blood donors (n = 935)] and patients before heparin therapy (n = 1207). In patients with suspected HIT, we compared the correlation of EIA‐IgG reactivities (Greifswald laboratory; n = 2821) and the heparin‐induced platelet activation assay (HIPA) with the correlation of reactivities of another EIA‐IgG (McMaster laboratory; n = 1956) with the serotonin‐release assay (SRA). Results: PF4/heparin‐IgG EIA OD reactivities had a lower OD 97.5th percentile in blood donors compared with patient groups before heparin treatment (P < 0.001). The percentage of sera testing positive in the functional assays strongly correlated with PF4/heparin‐IgG EIA OD reactivities in both laboratories with very similar results (correlation coefficient > 0.9) when normalized OD ranges (maximum OD divided by 10) were used instead of absolute OD values. Conclusions: Results of PF4/heparin‐IgG EIA should not be reported as only positive or negative as there is no single acceptable cut‐off value. Instead, reporting PF4/heparin‐IgG EIA OD results in ranges allows for risk‐stratified prediction for presence of platelet‐activating antibodies. Use of normalized OD ranges permits a standardized approach for inter‐laboratory comparisons.