Value of SDS-polyacrylamide gel electrophoresis, small molecular weight proteins and alpha-1-acid glycoprotein for the diagnosis of tubular damage.

The low molecular weight proteins alpha-1-microglobulin, beta-2-microglobulin, retinol binding protein, alpha-1-acid glycoprotein and the SDS-polyacrylamide gel electrophoresis (SDS-PAGE) were estimated in 31 healthy children and compared to 81 urine samples of children with tubular damage (TD). The tubular damage was diagnosed clinically and established by beta-2-microglobulin determination. Means for healthy children were: beta-2-microglobulin 109 +/- 77 micrograms/l, alpha-1-microglobulin 0.39 +/- 0.0 mg/dl, retinol binding protein 0.49 +/- 0.0 mg/dl, alpha-1-acid glycoprotein 0.69 +/- 0.0 mg/dl. Means for children with TD were: beta-2-microglobulin 8530 +/- 14693, alpha-1-microglobulin 2.98 +/- 2.28 mg/dl, retinol binding protein 1.68 +/- 2.44 mg/dl and alpha-1-acid glycoprotein 2.79 +/- 3.44 mg/dl. Comparing the panel of healthy children with sick children (TD) we found the following: b2m t = 3.2, p = less than 0.0005, a1m t = 6.5, p = less than 0.0005, rbp t = 2.65, p = less than 0.0005, a-1-agp t = 3.4, p = less than 0.005. a1m revealed tubular damage in 77 out of 81 tubular disorders, the rbp in 25 out of 81 and alpha-1-acid glycoprotein showed tissue damage or inflammation in 33 out of 81 patients. SDS-PAGE revealed tubular damage in 46 out of 81 patients with TD. We can assay that alpha-1-microglobulin is a useful marker for tubular damage. The determination of retinol binding protein and alpha-1-acid glycoprotein is useless for this purpose. The SDS-PAGE, though a potent tool for the differential diagnosis between glomerular or tubular damage, alone is not a reliable assay for the diagnosis of TD.