Potassium regulation appears to differ in patients with polycystic kidney disease (PKD) compared with other etiologies of chronic kidney disease (CKD), according to the authors of a new study.

In an analysis of 1788 patients from the KNOW-CKD study (KoreaN cohort study for Outcome in patients With Chronic Kidney Disease), patients with PKD had significantly lower serum potassium levels and lower risks for hyperkalemia than other CKD etiologies during CKD stages 1 to 3b. Hyperkalemia prevalence was also lower among the 293 PKD patients than the other CKD groups up to CKD stage 3 to 4. In adjusted analyses, the risk for hyperkalemia was 5 times higher with diabetic nephropathy, 3 times higher with hypertensive nephrosclerosis, and twice as high with glomerulonephritis, than with PKD.

“Taking these results together, it can be suggested that patients with PKD may have a lower risk of hyperkalemia than those with other etiologies of CKD,” Hyoungnae Kim, MD, of Yonsei University in Seoul, and colleagues stated in BMC Nephrology. They added that further use of dual renin-angiotensin-aldosterone system (RAAS) inhibition may be beneficial in decreasing high intrarenal RAAS activity with a low risk of hyperkalemia in patients with PKD.

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The team investigated renal potassium handling by measuring urinary angiotensinogen (AGT), a marker of intrarenal RAAS activity. In multivariable linear regression analysis, having a higher urinary AGT to creatinine (Cr) ratio correlated with lower serum potassium. The ratio appeared significantly higher in PKD patients than in other CKD patients. PKD patients also had a significantly higher transtubular potassium gradient (of urinary to serum potassium) that correlated with the AGT to Cr ratio. In PKD patients, a high urinary AGT to Cr ratio was associated with significantly increased risks for kidney function decline and all-cause mortality by 29%.

“In our study, we also showed that urinary AGT/Cr ratio was correlated with decline in renal function and mortality in patients with PKD. To our knowledge, this is the first longitudinal study that has shown urinary AGT as a prognostic marker in patients with PKD,” Dr Kim and his collaborators stated. The researchers acknowledged that the urinary AGT to Cr ratio can be increased with proteinuria, so additional studies are warranted.

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Kim H, Park S, Hyun Jhee J, et al. Urinary angiotensinogen level is associated with potassium homeostasis and clinical outcome in patients with polycystic kidney disease: a prospective cohort study. BMC Nephrol. 2019;20:104. DOI:10.1186/s12882-019-1292-3