Objective: To determine the agreement between plasma total solids (TS) concentration as measured by refractometry and plasma total protein (TP) concentration as measured by biuret assay in pet rabbits and ferrets.
Sample: 253 and 146 blood samples from 146 and 121 ferrets and rabbits, respectively, with results of CBC and plasma biochemical analyses.
Procedures: Data were collected from medical records regarding plasma TS and TP concentrations, PCV, plasma biochemical values, plasma appearance, and patient signalment. Agreement was determined between refractometer and biuret assay (reference method) values for plasma TS and TP concentration. Other variables were examined for an impact on this agreement.
Results: Mean ± SD plasma TP and TS concentrations were 6.4 ± 0.8 mg/dL and 6.6 ± 0.8 mg/dL, respectively, for rabbits and 6.3 ± 1.2 mg/dL and 6.4 ± 1.1 mg/dL for ferrets. On average, refractometer values overestimated plasma TP concentrations as measured by biuret assay. Plasma cholesterol, glucose, and BUN concentrations and hemolysis and lipemia had significant effects on this bias for ferrets; only BUN concentration had an effect on bias for rabbits given the available data. Other variables had no influence on bias. The limits of agreement were wider than the total allowable analytic error, and > 5% of the data points were outside acceptance limits, indicating that the 2 methods were not in clinical agreement.
Conclusions and clinical relevance: Refractometer measurements of plasma TS concentration failed to provide a good estimation of biuret assay measurements of plasma TP concentration in rabbits and ferrets, suggesting that these 2 analytic methods and the results they yield cannot be used interchangeably in these species.