Refractometric total plasma protein measurement as a cage-side indicator of hypoalbuminemia and hypoproteinemia in hospitalized dogs

Abstract

To assess the relationship between total plasma protein (TPP) as measured by refractometry and serum hypoalbuminemia and hypoproteinemia in hospitalized dogs. Retrospective, observational study conducted over 6-month period between March and August 2008. University teaching hospital. Four hundred and three hospitalized dogs in an ICU. None. TPP, serum albumin, total protein, glucose, urea, cholesterol was measured from dogs enrolled in study. TPP was evaluated as a predictor for hypoalbuminemia defined both as albumin <25 g/L (<2.5 g/dL) and albumin <20 g/L (<2.0 g/dL), and serum hypoproteinemia, defined as serum total protein <40 g/L (<4.0 g/dL), using logistic regression. Impact of glucose, urea, cholesterol, and total bilirubin on refractometric readings were also assessed. TPP predicted hypoalbuminemia at albumin concentrations of <25 g/L (<2.5 g/dL) and <20 g/L (<2.0 g/dL) (P<0.001). A TPP<60 g/L (<6.0 g/dL) predicted albumin <25 g/L (<2.5 g/dL) with 73% sensitivity and 86% specificity. A TPP<58 g/L (<5.8 g/dL) predicted a serum albumin <20 g/L (<2.0 g/dL) with 70% sensitivity and 80% specificity. For dogs with known risk factors where specificity optimization may be appropriate, refractometer TPP<50 g/L (<5.0 g/dL) and <48 g/L (<4.8 g/dL) predicted hypoalbuminemia at each level with >95% specificity, although sensitivity was poor. Refractometer TPP<58 g/L (<5.8 g/dL) predicted serum total protein of <40 g/L (<40 g/dL) with sensitivity of 82% and specificity of 84%. Hypercholesterolemia and hyperglycemia significantly affected TPP readings; an increase in serum glucose by 10 mmol/L (180 mg/dL) was associated with an average independent increase in refractometer TPP of 2.27 g/L (0.23 g/dL) (P<0.001, 95% confidence interval=1.08-3.47) and an increase in serum cholesterol of 1 mmol/L (38.6 mg/dL) was associated with an average independent increase in refractometer TPP of 1.36 g/L (0.14 g/dL) (P<0.001, 95% confidence interval=1.12-1.59). Suboptimal sensitivity limits the use of refractometric TPP for prediction of hypoalbuminemia in the context of patient screening; a high proportion of false negatives may result. However, identification of a refractometric TPP<58 g/L is strongly indicative of both serum hypoalbuminemia and hypoproteinemia, with high specificity, and warrants further investigation. Refractometric readings may be falsely increased in patients with hyperglycemia or hypercholesterolemia.