Diagnostic value of low-molecular mass proteins in serum for the detection of reduced glomerular filtration rate.

The diagnostic value of the low-molecular mass proteins ribonuclease, beta 2-microglobulin, and lysozyme in serum for the detection of reduced glomerular filtration rates was evaluated. The values of these proteins and of serum creatinine investigated in 52 patients suffering from chronic renal diseases were plotted against 99m-Tc-diethylenetriaminopentaacetate clearance as an indicator of glomerular filtration rate. Log-transformed data showed a good fit of linearity. Considering the 95% confidence limits of the regression equations, ribonuclease increased above the normal range when the glomerular filtration rate was lower than 1.24 ml/s whereas the other analytes partly remained within their normal limits. Out of those 18 patients with glomerular filtration rates lower than 1.24 ml/s, all patients showed elevated ribonuclease levels. beta 2-Microglobulin, creatinine, and lysozyme were increased in 17, 14, and 12 cases, respectively. Ribonuclease and beta 2-microglobulin showed similar results when other diagnostic criteria (specificity, efficiency and predictive values) were taken into account. We recommend ribonuclease determination in serum for the detection of reduced glomerular filtration rate in the normal range of creatinine. The test is diagnostically powerful, cheap and easy to perform.