Urinary citrate as a marker of renal function in patients with autosomal dominant polycystic kidney disease

Introduction Autosomal dominant polycystic kidney disease (ADPKD) is frequent to find low urinary citrate levels. Recently, it has been suggested that urinary citrate could be a marker of covert metabolic acidosis in chronic kidney disease. Objective Our aim was to analyze relationship between urinary citrate levels, renal function, and serum bicarbonate in ADPKD patients. Methods We determined citrate in 24-h collected urine from ADPKD patients and correlated with glomerular filtration rate (CKD-EPI equation) and serum bicarbonate concentration. Results We included 120 patients, 60% men, eGFR was 71 ± 32 mL/min/1.73 m 2 . Urinary citrate/creatinine ratio was 195 ± 152 mg/gCr (range 1.2–689) with levels significantly higher in females. Urinary citrate lower than 300 mg/gCr was present in 75% of patients and when considering chronic kidney stages (CKD), we observed reduced levels in 48.8% in CKD1 stage, in 79.4% in CKD2 stage, in 96.2% in CKD3 stage, and in 94.7% of patients in CKD4 stage. Urinary citrate was correlated with serum creatinine ( r = − 0.61, p < 0.001) and eGFR ( r = 0.55, p < 0.001) in both gender. We did not find any correlation with serum bicarbonate. Using a general linear modeling analysis, we found as predictors of urinary citrate/creatinine ratio to glomerular filtration rate, gender, and age. Lower levels of urinary citrate were accompanied by a decline in urinary osmolality and in renal excretion of calcium and uric acid. In a subgroup of patients, we measured total kidney volume and we found an inverse correlation with urinary citrate levels that disappeared when it was corrected with glomerular filtration rate. Conclusions Urinary citrate is very frequently reduced in ADPKD patients being present from very early CKD stages. Their levels in urine are inversely correlated with glomerular filtration rate and it is not related with serum bicarbonate concentration. We think that it would be interesting to study urinary citrate as a marker of chronic kidney disease in ADPKD patients.