Gout and age cause lower GFR

Gout and age cause lower GFR

Is low GFR caused by gout, age, or something else?

Gout and age cause lower GFR chart is from:
Gibson, T., J. Highton, C. Potter, and H. A. Simmonds. “Renal impairment and gout.” Annals of the rheumatic diseases 39, no. 5 (1980): 417.