Clinically relevant differences in prothrombin time and INR values related to blood sample collection in plastic vs glass tubes.
We compared prothrombin times (PTs) and international normalized ratios (INRs) for blood samples drawn into plastic vs glass collection tubes. We collected 60 venous blood samples into 4.5-mL glass and 2 plastic tubes (2.7 and 3.5 mL). An additional 153 samples, including 63 from warfarin-anticoagulated patients, were collected only in glass and 2.7-mL plastic tubes. The PTs and INRs were determined following routine laboratory procedures. A subset of 35 frozen aliquot samples was analyzed with a different instrument-reagent combination. The PTs and INRs for samples in plastic tubes were significantly lower than for samples in glass tubes. The mean INR differences increased with INR magnitude from approximately -0.1 (INR, 1.5) to -0.7 (INR, 4.5). Of the plastic tube INRs, 50% were more than 10% lower than INRs from samples collected in glass tubes. Therapeutic monitoring based on plastic-tube INRs could result in higher doses of warfarin.
Fiebig
Eberhard W
EW
Department of Laboratory Medicine, University of California San Francisco, USA.
Etzell
Joan E
JE
Ng
Valerie L
VL
D001800:Blood Specimen Collection / Q000295:instrumentation*; D005898:Glass; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods; D010969:Plastics; D011517:Prothrombin Time / Q000379:methods
D010969:Plastics