Evaluation of automated immunoassays in the diagnosis of heparin induced thrombocytopenia.
BACKGROUND
Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies that recognize platelet factor 4/heparin (PF4/hep) complexes. The in vitro demonstration of PF4/hep antibodies using functional and immunological methods is essential for optimal management of patients suspected to have HIT. Since functional assays are technically challenging and limited to specialized laboratories, antigen-binding assays are commonly used in routine laboratories.


METHODS
Blood samples from 448 consecutive patients in whom HIT was suspected were investigated using a latex agglutination test HemosIL® HIT-Ab(PF4-H) (HemosIL-Ab), two chemiluminescence tests HemosIL AcuStar HIT-Ab(PF4-H) (HemosIL AcuStar-Ab) and AcuStar HIT-IgG(PF4-H) (HemosIL AcuStar-IgG), an in-house PF4/hep IgG enzyme immunoassay (EIA) and the heparin induced platelet aggregation (HIPA) test.


RESULTS
Antibodies against PF4/hep were detectable in 44 out of 119 samples using HemosIL-Ab among which 20 samples were also reactive in the HIPA; and in 122, 64 and 108 out of 448 sera using HemosIL AcuStar-Ab, HemosIL AcuStar-IgG and in-house PF4/hep IgG-EIA, respectively, among which 52 sera were also reactive in the HIPA. All assays had high sensitivities of >95% for platelet activating antibodies; however, they differed in their specificities. The highest specificity and positive predictive value was observed by HemosIL AcuStar-IgG (96% and 78%, respectively).


CONCLUSIONS
Automated immunoassays are useful in the laboratory investigations of HIT and present a potential improvement toward standardization of laboratory investigations of HIT. The high positive predictive capability may justify treating the patient with alternative anticoagulants without waiting for the results of a functional assay.
Institute for Immunology and Transfusion Medicine, Ernst-Moritz-Arndt University Greifswald, Germany.
Karina
K
Althaus
Gregor
G
Hron
Ulrike
U
Strobel
Rosanna
R
Abbate
Angela
A
Rogolino
Simon
S
Davidson
Andreas
A
Greinacher
Tamam
T
Bakchoul
D000371:Agglutination; D001331:Automation; D006493:Heparin / Q000009:adverse effects* / Q000737:chemistry; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000737:chemistry; D007840:Latex / Q000737:chemistry; D049449:Luminescence; D010974:Platelet Aggregation; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013921:Thrombocytopenia / Q000139:chemically induced / Q000175:diagnosis* / Q000276:immunology*
D007074:Immunoglobulin G; D007840:Latex; D006493:Heparin