Christopher M.M. and O’neill S.
The objective of this study was to compare and investigate differences in glucose and lactate concentrations in sodium fluoride/potassium oxalate (NaF/Ox) plasma and serum in healthy cats and cats with metabolic disease. Glucose and lactate concentrations were determined in routinely processed serum and NaF/Ox plasma obtained from healthy (n=30), hyperthyroid (n=27) and diabetic (n=30) cats, and in samples from 6 healthy cats stored at 25 degrees C or 4 degrees C for 0, 1, 2, 4, or 8 hours. The packed cell volume (PCV) of blood collected in NaF/Ox was compared with that of blood collected in EDTA. Mean glucose concentration was significantly (P<.05) lower in NaF/Ox plasma than in serum in all groups of cats, by 0.7-2.5 mmol/L (11-45 mg/dL); the difference was greater in hyperthyroid and diabetic cats. In vitro, only serum stored on the clot for >/= 1 hour at 25 degrees C had significantly lower glucose and higher lactate concentrations. The PCV of NaF/Ox-anticoagulated blood was lower that that of EDTA-anticoagulated blood, by 7.0% +/- 1.4% (P<.01). In conclusion, collection of feline blood in NaF/Ox was necessary to prevent in vitro increases in lactate concentration; however, NaF/Ox artifactually decreased plasma glucose concentration because of RBC shrinkage. The PCV should not be determined on blood collected in NaF/Ox.