A new equation for calculation of colloid osmotic pressure based on serum total protein concentration and UV-light absorption

SummaryColloid osmotic pressure (COP) plays a major role in transcapillary fluid exchange. COP is generally calculated using the serum total protein (TP) concentration. The difference between calculated and measured COP may be considerable depending on albumin to globulin (A/G) ratio. There is a linear relationship between the absorbance and protein concentration. The aim of this study was to find an equation for calculation of COP based on serum TP and UV-light absorption. Serum samples with different A/G ratio were prepared in vitro, and COP, serum TP concentration and serum UV-light absorption (at 280 nm) were measured. The relationship between COP, serum TP concentration and UV-light absorption were determined. The validity of the obtained equations was confirmed by comparison between measured and calculated COP in 122 hospitalized patients and healthy individuals. By a linear curve fitting, the following equation was obtained for calculation of COP with a highly significant correlation (r2=0.92, p<0.05): COP=1.8×TP×Abs+5.5; where Abs is the serum UV-light absorption at 280 nm. This equation is accurate and simple formula for calculation of COP based on serum TP concentration and UV-light absorption and can be useful in clinic where colloid osmometers are not available.