Background and objectives Predictingdiseaseprogression in patientswith autosomaldominantpolycystic kidney disease (ADPKD) poses a challenge, especially in early- stage disease when kidney function... Show moreBackground and objectives Predictingdiseaseprogression in patientswith autosomaldominantpolycystic kidney disease (ADPKD) poses a challenge, especially in early- stage disease when kidney function is not yet affected. Ongoing growth of cysts causes maximal urine-concentrating capacity to decrease from early on. We therefore hypothesized that the urine-to-plasmaurea ratio, as a reflection of the urine-concentrating capacity, can be used as a marker to predict ADPKD progression. Design The urine- to-plasma urea ratio was calculated by dividing concentrations of early morning fasting spot urine urea by plasma urea. First, this ratio was validated as surrogate marker in 30 patients with ADPKD who underwent a prolongedwater deprivation test. Thereafter, associationwith kidney outcomewas evaluated in 583 patients with ADPKDwith a broad range of kidney function. Multivariable mixed-model regressionwas used to assess association with eGFR slope, and logarithmic regression to identify patients with rapidly progressive disease, using a cutoff of 23.0 ml/min per 1.73 m2 per year. The urine-to-plasma urea ratio was compared with established predictors, namely, sex, age, baseline eGFR, Mayo Clinic height-adjusted total kidney volume class, and PKD gene mutation. Results The maximal urine-concentrating capacity and urine-to-plasma urea ratio correlated strongly (R50.90; P,0.001). Next, the urine-to-plasma urea ratio was significantly associated with rate of eGFR decline during a median follow-up of 4.0 (interquartile range, 2.6-5.0) years, both crude and after correction for established predictors (b50.58; P50.02). The odds ratio of rapidly progressive diseasewas 1.35 (95% confidence interval, 1.19 to 1.52; P,0.001) for every 10 units decrease in urine-to-plasma urea ratio, with adjustment for predictors. A combined risk score of the urine-to-plasma urea ratio, MayoClinic height-adjusted total kidney volume class, and PKD mutation predicted rapidly progressive disease better than each of the predictors separately. Conclusions The urine-to-plasma urea ratio, which is calculated fromroutine laboratory measurements, predicts disease progression in ADPKD in addition to other risk markers. Show less
Background: Disease monitoring of autosomal dominant polycystic kidney disease (ADPKD) will become more important with potential upcoming therapeutic interventions. Because serum creatinine level... Show moreBackground: Disease monitoring of autosomal dominant polycystic kidney disease (ADPKD) will become more important with potential upcoming therapeutic interventions. Because serum creatinine level is considered of limited use and measurement of effective renal blood flow (ERBF) and total renal volume are time consuming and expensive, there is a need for other biomarkers. We aimed to investigate which urinary markers have increased levels in patients with ADPKD; whether these urinary markers are associated with measured glomerular filtration rate (mGFR), ERBF, and total renal volume; and whether these associations are independent of albuminuria (urine albumin excretion [UAE]). Study Design: Diagnostic test study. Setting & Participants: 102 patients with ADPKD (Ravine criteria) and 102 age-and sex-matched healthy controls. Index Test: 24-hour urinary excretion of glomerular (immunoglobulin G), proximal tubular (kidney injury molecule 1 [KIM-1], N-acetyl-beta-D-glucosaminidase, neutrophil gelatinase-associated lipocalin [NGAL], and beta(2)-microglobulin), and distal tubular (heart-type fatty acid binding protein [H-FABP]) damage markers and inflammatory markers (monocyte chemotactic protein 1 [MCP-1] and macrophage migration inhibitory factor). Reference Test: Disease severity assessed using measures of kidney function (mGFR and ERBF, measured using clearance of iothalamate labeled with iodine 125 and hippuran labeled with iodine 131 during continuous infusion, respectively) and structure (total renal volume, measured using magnetic resonance imaging). Other Measurements: 24-hour UAE. Results: In 102 patients with ADPKD (aged 40 +/- 11 years; 58% men), levels of all measured urinary biomarkers were increased compared with healthy controls. Excretion of immunoglobulin G and albumin relatively were most increased. ERBF and mGFR values were associated with urinary excretion of beta(2)-microglobulin, NGAL, and H-FABP independent of UAE, whereas total renal volume was associated with KIM-1, NGAL, and MCP-1 independent of UAE. Limitations: Cross-sectional, single center. Conclusions: Levels of markers for multiple parts of the nephron are increased in patients with ADPKD. In addition to measurement of UAE, measurement of urinary beta(2)-microglobulin, KIM-1, H-FABP, MCP-1, and especially NGAL could be of value for determination of disease severity in patients with ADPKD. Am J Kidney Dis 56: 883-895. (C) 2010 by the National Kidney Foundation, Inc. Show less
