Impact on result interpretation of correct and incorrect selection of veterinary glucometer canine and feline settings.

Veterinary glucometers should be correctly coded for the patient species; however, coding errors occur in clinical settings and the impact of such errors has not been characterized. We compared glucose concentrations in 127 canine and 37 feline samples using both canine and feline settings on a veterinary glucometer (AlphaTrak; Zoetis). All samples were measured first on the canine setting and then measured using the feline setting. Glucose concentration was also measured using a central laboratory biochemical analyzer (Cobas c311; Roche). Three data comparisons for each species were investigated: incorrectly coded glucometer vs. correctly coded glucometer, correctly coded glucometer vs. Cobas c311, and incorrectly coded glucometer vs. Cobas c311. For each comparison, the following analyses were conducted: Spearman rank correlation coefficient, Bland-Altman difference plot analysis, mountain plot analysis, and Deming regression. For clinical context, Clarke error grids were constructed. There was high positive correlation for all comparisons with both species. For all comparisons, mean difference was low (-0.7 to 0.5 mmol/L for canine samples, 1.0-2.0 mmol/L for feline samples). Incorrect glucometer coding resulted in proportional bias for canine samples and positive constant bias for feline samples, and individual differences could be large (-4.44 mmol/L for one dog, 6.16 mmol/L for one cat). Although the glucometer should be used per the manufacturer's recommendation, coding errors are unlikely to have severe adverse clinical consequences for most patients based on error grid analysis.

Excess EDTA interferes with cortisol measurement using a solid-phase, chemiluminescent enzyme immunoassay.

Hormone assays that use a solid-phase, automated, chemiluminescent enzyme immunoassay (CEIA) with an alkaline phosphatase-tagged hormone or antibody as a reporter are performed on serum or EDTA plasma in our laboratory. CEIA cortisol results appeared to increase in the presence of excess EDTA. We investigated the effect of the addition of different amounts of EDTA on cortisol concentrations in pooled canine serum samples. The recommended EDTA plasma concentration of 4.1 mmol/L (1.8 mg/mL) did not alter cortisol concentrations when added to serum pools; however, the addition of ≥5.1 mmol/L (2.25 mg/mL) of EDTA increased apparent concentrations of cortisol. Supplementation of serum samples with MgCl2 to 5 mmol/L reversed the effect of EDTA up to a concentration of ~8.1 mmol/L (3.6 mg/mL). Our findings show that CEIA cortisol results on EDTA plasma can be artificially increased if the EDTA concentration exceeds 5.1 mmol/L.