Globulin correction of the albumin gradient: correlation with measured serum to ascites colloid osmotic pressure gradients

Abstract

The albumin difference or gradient between serum ascites is presumed to be an effective estimate of the colloid osmotic pressure gradient, although this has never been directly demonstrated. The colloid osmotic pressure gradient is controlled by the degree of portal hypertension. Thus the albumin gradient is clinically useful in detecting patients with ascites caused by portal hypertension, although some overlap in such patients' albumin gradients exists compared with those of patients without portal hypertension. Part of this overlap is related to the inverse correlation of the albumin gradient with serum globulin; globulins also contribute to colloid osmotic pressure. The ability to calculate colloid osmotic pressure in serum and ascites with albumin and globulin concentration or to correct the albumin gradient for the impact of globulins might improve the clinical usefulness of the ascitic fluid analysis in determining the presence of portal hypertension in ascitic patients with borderline albumin gradients. Thus we developed equations to calculate colloid osmotic pressure from multivariate discriminate analyses of albumin and globulin concentrations in serial dilution samples of pooled serum and subsequently validated these equations, along with older methods of calculating colloid osmotic pressure. In an initial set of dilution experiments, globulin concentration was closely correlated with the colloid osmotic pressure to albumin concentration ratio (r = 0.956; p less than 0.001). Multivariate discriminate analysis yielded an equation for calculating colloid osmotic pressure from albumin (A) and globulin (G) concentration with a ratio of colloid osmotic pressure to albumin (calculated colloid osmotic pressure = A(1.058G + 0.163A + 3.11) and two other equations.(ABSTRACT TRUNCATED AT 250 WORDS)