Effect of subcutaneous administration of dalteparin on lupus anticoagulant assays.
BACKGROUND
Treatment with unfractionated heparin (UH) is known to affect screening tests for lupus anticoagulant (LA). False positive test results are common because confirmatory steps lack sufficient specificity to distinguish between LA and the presence of heparin. In this study, we wanted to see if therapeutic levels of low-molecular weight heparin (LMWH) may cause false positive tests for LA or alter the LA test results in LA-positive patients. We also wanted to evaluate the need to include heparin-neutralizing agents in the reagents.


METHODS
Six healthy subjects without LA and six LA-positive patients were given 100 IU/kg dalteparin subcutaneously (s.c.). Samples for three in-house and two commercially available LA tests were taken before and 4 h after the injection. LA test results were calculated as normalized screening/confirm ratios or as recommended by the manufacturers.


RESULTS
With both healthy subjects and LA patients, only small and clinically unimportant differences in mean clotting times and final test results were seen 4 h after subcutaneous dalteparin injections, at anti-FXa activities within the therapeutic range.


CONCLUSIONS
Our study with dalteparin suggests that LMWH therapy with plasma concentrations within the therapeutic range does not cause false positive tests for LA when normalized screening/confirm ratios are applied; nor do test results for LA-positive patients seem to be significantly altered. Heparin-neutralizing agents did not influence test performance.
Liestøl
Sigurd
S
Haematological Research Laboratory, Medical Clinic, Ullevål University Hospital, N-0407 Oslo, Norway. sigurdli@ioks.uio.no
Wisløff
Finn
F
D000328:Adult; D001780:Blood Coagulation Tests; D017985:Dalteparin / Q000008:administration & dosage*; D005189:False Positive Reactions; D005260:Female; D006493:Heparin / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007279:Injections, Subcutaneous; D016682:Lupus Coagulation Inhibitor / Q000032:analysis* / Q000097:blood; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D016682:Lupus Coagulation Inhibitor; D006493:Heparin; D017985:Dalteparin