Heida JE, Gansevoort RT, Messchendorp AL, et al. - Whether urine-to-plasma urea ratio, as a reflection of the urine-concentrating capacity, can serve as a marker to predict autosomal dominant polycystic kidney disease (ADPKD) progression, was investigated herein. Experts divided levels of early morning fasting spot urine urea by plasma urea in order to calculate urine-to-plasma urea ratio. A strong correlation between maximal urine-concentrating capacity and urine-to-plasma urea ratio was identified. For every 10 units reduction in urine-to-plasma urea ratio, the estimated odds ratio of rapidly progressive disease was 1.35, with adjustment for predictors. A better prediction of rapidly progressive disease was achieved with a combined risk score of the urine-to-plasma urea ratio, Mayo Clinic height-adjusted total kidney volume class, and PKD mutation vs each of the predictors separately. Overall, findings demonstrated that ADPKD progression was predicted by urine-to-plasma urea ratio, which was calculated from routine laboratory measurements, in addition to other risk markers.