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


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.
Greinacher
A
A
Institut für Immunologie und Transfusionsmedizin, Ernst-Moritz-Arndt Universität, Greifswald, Germany. greinach@uni-greifswald.de
Ittermann
T
T
Bagemühl
J
J
Althaus
K
K
Fürll
B
B
Selleng
S
S
Lubenow
N
N
Schellong
S
S
Sheppard
J I
JI
Warkentin
T E
TE
D000328:Adult; D000368:Aged; D005260:Female; D006493:Heparin / Q000009:adverse effects / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods; D007074:Immunoglobulin G / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D010978:Platelet Factor 4 / Q000737:chemistry*; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results; D012306:Risk; D012701:Serotonin / Q000737:chemistry; D012737:Sex Factors; D013921:Thrombocytopenia / Q000378:metabolism*
D007074:Immunoglobulin G; D012701:Serotonin; D010978:Platelet Factor 4; D006493:Heparin