Comparison of refractometry and biuret assay for measurement of total protein concentration in canine abdominal and pleural fluid specimens.

OBJECTIVE: To compare total protein (TP) concentrations in canine pleural and abdominal fluid specimens as measured by refractometry and biuret assay. DESIGN: Diagnostic test evaluation. SAMPLE: Data regarding 92 pleural and 148 abdominal fluid specimens from dogs with various diseases. PROCEDURES: TP concentrations in fluid specimens as measured by refractometry and biuret assay were recorded. Strength of association between sets of measurements was assessed by Spearman rank correlations and Bland-Altman plots. Optimal concentration cutoff for diagnostic discrimination between exudate and nonexudate was identified by construction of receiver operating characteristic curves. RESULTS: Median TP concentration in pleural fluid specimens was 2.7 g/dL (range, 0.3 to 4.8 g/dL) for refractometry and 2.9 g/dL (range, 0.7 to 5.8 g/dL) for biuret assay. Median TP concentration in abdominal fluid specimens was 3.5 g/dL (range, 0.1 to 6.0 g/dL) for refractometry and 3.5 g/dL (range, 0.6 to 5.7 g/dL) for biuret assay. Correlation was significant between refractometric and biuret results for pleural (ρ = 0.921) and abdominal (ρ = 0.908) fluid. Bland-Altman plots revealed bias of -0.18 g/dL for pleural fluid and -0.03 g/dL for abdominal fluid for refractometry versus biuret assay. With a TP concentration of ≥ 3 g/dL used to distinguish exudate from nonexudate, sensitivity of refractometry was 77% for pleural fluid and 80% for abdominal fluid. Specificity was 100% and 94%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Refractometry yielded acceptable results for measurement of TP concentration in canine pleural and abdominal fluid specimens, providing a more rapid and convenient method than biuret assay.

Comparison of manual and laboratory PCV and total protein using EDTA and lithium heparin canine samples.

OBJECTIVES: To evaluate if lithium heparin (LiH) and potassium ethylenediaminetetraacetic acid (EDTA) can be used interchangeably to obtain packed cell volume (PCV) and total protein by refractometry (TPr), and to compare those values with laboratorywderived haematocrit (Hct) and total protein (TP) concentration, respectively, in canine blood samples. METHODS: Blood samples taken in LiH and EDTA were manually assessed for PCV and TPr. Results were correlated to Hct and TP. RESULTS: 238 EDTA and corresponding serum/LiH samples were obtained. There was excellent correlation but statistically significant difference between LiH and EDTA PCV (n=43). LiH and EDTA TPr (n=43) were excellently correlated without significant difference. PCV and Hct (n=176) were excellently correlated without significant difference. LiH (n=105) and serum (n=133) TP was respectively fairly or well correlated with TPr but with significant differences. An increase in cholesterol of 1 mmol/L was associated with a mean independent increase in TPr of approximately 1 g/L. CLINICAL SIGNIFICANCE: LiH and EDTA can be used interchangeably for TPr. Although TPr and serum/plasma TP were correlated, there were statistically significant differences that could impact on clinical decision making. TPr is increased by cholesterol but this alone could not account for the magnitude of the difference observed.