Measurements of serum colloid osmotic pressure are of limited usefulness

We examined the usefulness of serum colloid osmotic pressure measurement in patients with chronic rather than acutely occurring low serum protein concentrations. We used two oncometers, the IL 186 Weil Oncometer and the Wescor Model 4100; results from the two instruments were interchangeable. Values for the colloid osmotic pressure were compared with those for serum total protein (r = 0.783) and albumin concentrations (r = 0.882), which were similar to previously published values. Our day-to-day CV was 2.8%. In studying over 100 patients we found that the previously reported occurrence of pulmonary edema in almost all patients whose colloid osmotic pressure was less than 12.5 mmHg was not seen in the chronic hypoproteinemic patients. We noted only one fatality in our patients whose colloid osmotic pressure was less than 10.5 mmHg, a value found to be associated with fatality in one previous study of acutely ill patients. Factors such as ambulation, fasting, dehydration, and the nature of the blood sample can markedly affect the value for colloid osmotic pressure value, and this, coupled with the good correlation with the serum albumin in several studies, leads us to question the usefulness of measuring colloid osmotic pressure in a non-specialist hospital environment, either as an adjunct to the measurement of serum protein or albumin, or as an independent test.