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

Alexandra Rose Small Animal Internal Medicine Service, Justus-Liebig University, 35392 Giessen, Germany.

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Deborah Funk Small Animal Internal Medicine Service, Justus-Liebig University, 35392 Giessen, Germany.

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Reto Neiger Small Animal Internal Medicine Service, Justus-Liebig University, 35392 Giessen, Germany.

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DOI:
https://doi.org/10.2460/javma.248.7.789
Volume/Issue:
Volume 248: Issue 7
Online Publication Date:
01 Apr 2016
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Abstract

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. (J Am Vet Med Assoc 2016;248:789–794)

Abstract

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. (J Am Vet Med Assoc 2016;248:789–794)

Contributor Notes

Address correspondence to Dr. Rose (alexandra.rose@gmx.at).
Cover Journal of the American Veterinary Medical Association
Journal of the American Veterinary Medical Association
Publication Date:
01 Apr 2016

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