We measured urinary enzyme activities, such as urinary-γ-glutamyl transpeptidase (U-γ-GTP) and microalbumin in 77 gouty patients without overt protei nuria, hypertension or diabetes mellitus in order to estimate renal derangement associated with gout, and investigated the relationship between these parameters and other renal function tests. Mean U-γ-GTP index was significantly higher in gouty patients than that in control subjects (p< 0.01), and U-γ-GTP index over 48 U/g⋅Cr was seen in 45.5% of gouty patients. Microalbuminuria, and elevated levels of urinary alanine aminopeptidase(U-AAP), urinary N-acetyl-β-glucosaminidase(U-NAG), urinary β2-microglobulin(U-β2-MG) and serum β2-microglobulin(S-β2-MG) were noted in 12.9%,11.7%,7.8%,5.2% and 6.5%of the gouty patients, respectively.
The levels of S-β2-MG and U-β2-MG were not different for patients with U-γ-GTP index of more than 48 U/g⋅Cr and those with U-γ-GTP index of less than 48U/g⋅Cr. However, a high level of U-NAG and significantly low level of Ccr were noted in patients having U-γ-GTP index over 48 U/g⋅Cr. The results of Fishberg's concentration test were not different for the two groups. As a result, it is considered to be desirable to perform simultaneous measurement of U-γ-GTP, U-NAG and U-β2-MG in evaluating whether or not proximal tubular damage really exists in gouty patients. In addition, microalbuminuria over 15μg/ml was seen in some patients without elevated levels of S-β2-MG. Therefore, it is suggested that microalbuminuria level is a sensitive indicator of renal damage, especially that of the glomerulus. However, whether microalbuminuria level can be used to predict the progression of gouty nephropathy remains unclear and will require long-term follow-up studies.
