Beta 2-microglobulin excretion and urinary cytology in analgesic nephropathy

Patients with analgesic nephropathy are at risk from uro-epithelial malignancy. Enhanced secretion of beta 2-microglobulin occurs from epithelial cancer cells. In order to find a screening test for malignancy in analgesic nephropathy, urinary levels of this protein were measured in patients with analgesic nephropathy with urine cytological abnormalities and were compared to a control group with glomerulonephritis. Mean fractional excretion of beta 2-microglobulin was higher (8.61 +/- 1.76 SEM) in patients with analgesic nephropathy than in those with glomerulonephritis (1.13 +/- 0.76) (P less than 0.025). Those patients with analgesic nephropathy who had malignant cells in the urine had higher mean fractional excretion (18.56 +/- 5.77) than those with only atypical cells (8.5 +/- 2.0) (P less than 0.05) who in turn had higher mean values than those with normal cytology (2.12 +/- 0.62) (P less than 0.0025). It is suggested that the increased beta 2-microglobulin excretion in analgesic nephropathy is due to secretion from abnormal urothelial cells as well as reduced tubular catabolism. Beta 2-microglobulin may be of use as a screening test for malignancy in analgesic nephropathy.