Morning urine-to-plasma urea ratio predicts polycystic kidney disease progression
Measuring urine-to-plasma urea ratio in the early morning was “the best representative of the urine-concentrating capacity” and predicted kidney function decline in patients with autosomal dominant polycystic kidney disease.
“Predicting disease progression in patients with autosomal dominant polycystic kidney disease (ADPKD) poses a challenge, especially in early stage disease when kidney function is not yet affected,” Judith E. Heida, MD/PhD candidate at the University Medical Center Groningen in the Netherlands, and colleagues wrote. “Ongoing growth of cysts causes maximal urine-concentrating capacity to decrease from early on. We therefore hypothesized that the urine-to-plasma urea ratio, as a reflection of the urine-concentrating capacity, can be used as a marker to predict ADPKD progression.”
First validating the urine-to-plasma urea ratio — calculated by dividing concentrations of early morning fasting spot urine urea by plasma urea — in patients with ADPKD who underwent a prolonged water deprivation test, researchers examined its association with kidney outcomes in 583 patients with ADPKD and a “broad range of kidney function.”
Researchers then compared the urine-to-plasma urea ratio with established predictors of disease progression (eg, sex, age, baseline eGFR, Mayo Clinic height-adjusted total kidney volume class [htTKV] and PKD gene mutation).
Participants were followed for a median of 4 years (an average of 10 eGFR measurements per individual; mean annual eGFR decline, 3.49 mL/min/1.73m2).
“The association of baseline urine-to-plasma urea ratio with subsequent decline in kidney function was statistically significant even when corrected for all established disease prediction markers (sex, baseline age, eGFR, Mayo Clinic htTKV class, and PKD mutation),” the researchers wrote, concluding that “the extent to which the kidneys can maximally concentrate urine is associated with disease severity (eGFR and TKV) and disease progression (rate of kidney function decline).
“Our data show that the early morning fasting urine-to-plasma urea ratio is a good surrogate for maximal urine-concentrating capacity [and] holds promise as an easy to measure novel predictor for rapid disease progression in patients with ADPKD.”
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