False-positive tests for heparin-induced thrombocytopenia in patients with antiphospholipid syndrome and systemic lupus erythematosus.
BACKGROUND
Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy that can be associated with arterial or venous thrombosis and is caused by antibodies against platelet factor 4 (PF4)-heparin complex. Patients with antiphospholipid syndrome (APS) have been reported with positive tests for PF4-heparin complex antibodies by antigen assay. Whether such patients can be treated with heparin is a dilemma.


OBJECTIVE
To determine the incidence and nature of the HIT immune reaction in patients with APS and/or systemic lupus erythematosus (SLE).


METHODS
Antibodies against PF4-heparin complex were assayed by particle gel immunoassay (PaGIA), or enzyme immunoassay (EIA) with or without an excess of heparin. EIA for PF4 alone was also performed. Functional assays for HIT, that is, heparin-induced platelet activation (HIPA) and heparin-induced platelet aggregation, were also performed.


RESULTS
In 32 of 42 patients (76.2%) with APS, APS and SLE, SLE, or SLE with antiphospholipid antibodies, EIA IgG or PaGIA for PF4-heparin complex antibodies were positive. Of these 32 samples, 26 (81.3%) tested positive for anti-PF4 antibodies. All 24 samples that were positive for PF4-heparin complex by EIA IgG were also positive for EIA IgG in the presence of heparin excess, and all were negative by the HIPA and heparin-induced platelet aggregation tests.


CONCLUSIONS
A large proportion of patients with APS and/or SLE give false-positive HIT antigen test results that are presumably related to autoantibodies against PF4, which can be distinguished from true HIT antibodies by EIA for PF4-heparin complexes tested with heparin excess, and by functional assays.
Pauzner
R
R
Department of Internal Medicine E, Sheba Medical Center and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Greinacher
A
A
Selleng
K
K
Althaus
K
K
Shenkman
B
B
Seligsohn
U
U
D000328:Adult; D016736:Antiphospholipid Syndrome / Q000150:complications*; D005189:False Positive Reactions; D005260:Female; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000150:complications*; D008297:Male; D008875:Middle Aged; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000150:complications / Q000175:diagnosis
D006493:Heparin