Total protein determination in pigeon plasma and serum: comparison of refractometric methods with the biuret method

Total protein concentration established by the biuret method in plasma and serum from pigeons was compared with results obtained by temperature-compensated and nontemperature-com- pensated refractometers in plasma. Plasma total protein concentration and serum total protein con- centration measured by the biuret method were highly correlated (r = 0.99); plasma values were on average 1.74 g higher than serum values because of the presence of fibrinogen. Values obtained by refractometer were higher than values obtained by the biuret method. Values obtained by the temperature-compensated refractometer were significantly higher than those obtained by the non- temperature-compensated refractometer and were not considered to be accurate. Plasma protein concentration measured by refractometer can only be considered a rough estimate of total protein concentration obtained by the biuret method (r = 0.89) after applying a correction formula for the species and specific refractometer.