A comparative study of three kidney biomarker tests in autosomal-dominant polycystic kidney disease

BACKGROUND: The relationship between the progress of tubular damage and renal insufficiency in autosomal-dominant polycystic kidney disease (ADPKD) is a subject of doubtless interest, and is the object of this present work. METHODS: A total of 92 adult ADPKD patients of both genders were studied, none of which presented end-stage renal disease (ESRD), and classified according to an ultrasound score based on kidney size and number of cysts. Urinary albumin and beta-N-acetylhexosaminidase (Hex) and its isoenzymes were determined, together with serum glutathione peroxidase, cystatin C, creatinine, and urea. RESULTS: A frequent elevation of the urinary Hex was found and an alteration of its isoenzymatic profile, with 31% of the normotensive patients with normoalbuminuria already presenting an increased proportion of Hex B isoenzyme. Keeping age constant, a partial significant correlation was found between the ultrasound score and the proportion of Hex B (r = 0.352, P < 0.05), but not with albuminuria or cystatin C. In 42 patients the different biochemical variables were again determined after 1 year, finding that in the 13 normotensive patients with normoalbuminuria there had been a significant decrease in the concentration of cystatin C (P < 0.05), and a significant increase in the urinary excretion of albumin and Hex B isoenzyme (P < 0.05). By the other hand, in the other 29 patients with micro- or macroalbuminuria and hypertension, no significant differences were found. CONCLUSION: The results point toward an important participation of tubular damage in the pathogenesis of this disease. It may also be suggested that in normotensive and normoalbuminuric ADPKD patients, a gradual increase of glomerular filtration would be produced. After the start of hypertension and microalbuminuria, the glomerular filtration rate (GFR) would decrease progressively, although more slowly.