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Refractometric total protein concentrations in icteric serum from dogs

Aradhana Gupta DVM, MVSc1 and Steven L. Stockham DVM, MS2
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  • 1 Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.
  • | 2 Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

Abstract

Objective—To determine whether high serum bilirubin concentrations interfere with the measurement of serum total protein concentration by refractometry and to assess potential biases among refractometer measurements.

Design—Evaluation study.

Sample—Sera from 2 healthy Greyhounds.

Procedures—Bilirubin was dissolved in 0.1M NaOH, and the resulting solution was mixed with sera from 2 dogs from which food had been withheld to achieve various bilirubin concentrations up to 40 mg/dL. Refractometric total protein concentrations were estimated with 3 clinical refractometers. A biochemical analyzer was used to measure biuret assay–based total protein and bilirubin concentrations with spectrophotometric assays.

Results—No interference with refractometric measurement of total protein concentrations was detected with bilirubin concentrations up to 41.5 mg/dL. Biases in refractometric total protein concentrations were detected and were related to the conversion of refractive index values to total protein concentrations.

Conclusions and Clinical Relevance—Hyperbilirubinemia did not interfere with the refractometric estimation of serum total protein concentration. The agreement among total protein concentrations estimated by 3 refractometers was dependent on the method of conversion of refractive index to total protein concentration and was independent of hyperbilirubinemia.

Abstract

Objective—To determine whether high serum bilirubin concentrations interfere with the measurement of serum total protein concentration by refractometry and to assess potential biases among refractometer measurements.

Design—Evaluation study.

Sample—Sera from 2 healthy Greyhounds.

Procedures—Bilirubin was dissolved in 0.1M NaOH, and the resulting solution was mixed with sera from 2 dogs from which food had been withheld to achieve various bilirubin concentrations up to 40 mg/dL. Refractometric total protein concentrations were estimated with 3 clinical refractometers. A biochemical analyzer was used to measure biuret assay–based total protein and bilirubin concentrations with spectrophotometric assays.

Results—No interference with refractometric measurement of total protein concentrations was detected with bilirubin concentrations up to 41.5 mg/dL. Biases in refractometric total protein concentrations were detected and were related to the conversion of refractive index values to total protein concentrations.

Conclusions and Clinical Relevance—Hyperbilirubinemia did not interfere with the refractometric estimation of serum total protein concentration. The agreement among total protein concentrations estimated by 3 refractometers was dependent on the method of conversion of refractive index to total protein concentration and was independent of hyperbilirubinemia.

Contributor Notes

Presented in abstract form at the Annual Meeting of the American Society for Veterinary Clinical Pathology, Seattle, November 2012.

The authors thank Janice Muller, Jill Newland, Jessica Penner, and Stephanie Ochoa for technical assistance.

Address correspondence to Dr. Stockham (stockham@vet.k-state.edu).