Refractometric total protein concentrations in icteric serum from dogs

Area of Science:

• Veterinary Clinical Pathology
• Analytical Chemistry

Background:

• Refractometry is a common method for estimating serum total protein concentration in veterinary diagnostics.
• Hyperbilirubinemia, a condition of elevated bilirubin, can potentially interfere with spectrophotometric and other analytical methods.

Purpose of the Study:

• To evaluate the interference of high serum bilirubin concentrations on refractometric total protein measurements.
• To assess potential biases among different clinical refractometers in estimating total protein.

Main Methods:

• An evaluation study using sera from two healthy Greyhounds was conducted.
• Bilirubin was added to sera to achieve concentrations up to 40 mg/dL.
• Serum total protein was measured using three clinical refractometers and a biochemical analyzer (biuret assay).

Main Results:

• No interference was observed with refractometric total protein measurements even at bilirubin concentrations up to 41.5 mg/dL.
• Significant biases were detected in refractometric total protein concentrations.
• These biases were directly related to the conversion method of refractive index to total protein concentration.

Conclusions:

• Hyperbilirubinemia does not interfere with the refractometric estimation of serum total protein concentration.
• Agreement between refractometers is dependent on the conversion algorithm used, independent of bilirubin levels.
• Standardization of refractive index to total protein conversion is crucial for accurate refractometric analysis.