Heparin-induced thrombocytopenia is a life threatening thrombotic disorder caused by antibodies to platelet factor 4 (PF4) and heparin. Commercial immunoassays are frequently used for the detection of PF4-heparin antibodies, and several studies have reported that higher antibody titers are more frequently associated with adverse events. It is not known if conditions involving sample preparation and/or storage affect the operational characteristics of PF4-heparin immunoassays. We compared the detection of PF4-heparin antibodies from 48 patient samples collected concordantly in serum separator tubes or tubes containing EDTA or sodium citrate. We also examined the effects of extended sample storage on whole blood collected in serum separator, EDTA, or citrate tubes at 4 degrees C for up to 96 hours on antibody detection. We noted that serum or plasma anticoagulated with sodium citrate or EDTA yielded comparable results. In addition, we could not demonstrate any significant sample deterioration after storage at 4 degrees C in any medium for up to 4 days. These findings suggest that PF4-heparin antibodies are largely insensitive to the effects of sample preparation and storage.