Urinary lactic dehydrogenase isoenzyme 5 in the differential diagnosis of kidney and bladder infections.

Urinary lactic dehydrogenase (U-LDH) isoenzyme assays were performed on ch2) as well as normal controls (N = 24). Docuemntation of bladder and kidney infection was accomplished by means of the bladder washout test, culture of ureteric urine (in patients with urinary diversion), kidney function studies including the maximal urine concentration test, clinical symptomatology and radiologic appearance of the urinary tract. Total U-LDH in normal children (10.8 +/- 1 mU/ml) was lower than in patients with bladder (27.0 +/- 3.9 mU/ml) or kidney (226 +/- 67.3 mU/ml) infections (P less than 0.005). In normal children isoenzymes 1 and 2 predominated (LDH-1 migrates fastest to anode -- fast zone pattern). In patients with bladder infections, the isoenzyme patterns varied but the concentration of isoenzyme 5 (3.1 +/- 0.8 mU/ml) was lower (P less than 0.005) than in patients with kidney infections (120 +/- 39 mU/ml). In the latter, isoenzymes 4 and 5 predominated (slow zone pattern). Since overlap between kidney and bladder infections regarding isoenzyme 5 concentrations (at 3 SD) occurred in only one individual (patient 37), a correct differential diagnosis using U-LDH-5 alone would have been possible in 94% of the children with pyelonephritis or 97% of the total patient population (kidney + bladder).