Beta 2-microglobulin and other proteins as parameter for tubular function.

Urinary excretion of the low molecular weight protein beta 2-microglobulin and tubular enzymes--alanine aminopeptidase (AAP), gamma-glutamyl transpeptidase (gamma-GT) and alkaline phosphatase (AP)--are very sensitive parameters for proximal tubular lesions. In patients with preeclampsia the renal excretion of beta 2-microglobulin allows to differentiate between a primary preeclampsia and a preeclampsia superimposed upon chronic pyelonephritis. In the first group the increase is 3- to 4-fold and in the second group up to 300-fold. In patients with kidney transplantation the urinary excretion of beta 2-microglobulin, AAP, gamma-GT and AP are several times higher than in normals. In case of a rejection episode a further increase of these proteins occur in more than 80% several days before clinical symptoms are present. The application of analgetics (paracetamol, acetylsalicylic acid) in healthy individuals in therapeutical dosages on 3 consecutive days does not show any tubular alteration by the measurement of urinary beta 2-microglobulin. Aminoglycosides (tobramycin, UK 18,892) lead to a cumulative increase of the renal excretion of beta 2-microglobulin and AAP while cephalosporins induce an increase of total proteins in the final urine under the same conditions.