Apolipoprotein L1 Genotypes and the Association of Urinary Potassium Excretion with CKD Progression.

Background And Objectives: Progressive CKD in Black individuals is strongly associated with polymorphisms in the gene, but it is unknown whether dietary risk factors for CKD progression vary in high- versus low-risk genotypes. We investigated if genotypes modify associations of dietary potassium and sodium with CKD progression and death.

Design, Setting, Participants, & Measurements: We analyzed 1399 self-identified Black participants enrolled in the Chronic Renal Insufficiency Cohort from April 2003 to September 2008. Exposures were calibrated 24-hour urine potassium and sodium excretion. The primary outcome was CKD progression defined as the time to 50% decline in eGFR or kidney failure. The secondary outcome was CKD progression or death. We tested for an interaction between urinary potassium and sodium excretion and genotypes.

Results: Median 24-hour urinary sodium and potassium excretions in Black participants were 150 mmol (interquartile range, 118-188) and 43 mmol (interquartile range, 35-54), respectively. Individuals with high- and low-risk genotypes numbered 276 (20%) and 1104 (79%), respectively. After a median follow-up of 5.23 years, CKD progression events equaled 605, and after 7.29 years, CKD progression and death events equaled 868. There was significant interaction between genotypes and urinary potassium excretion with CKD progression and CKD progression or death (=0.003 and =0.03, respectively). In those with high-risk genotypes, higher urinary potassium excretion was associated with a lower risk of CKD progression (quartiles 2-4 versus 1: hazard ratio, 0.83; 95% confidence interval, 0.50 to 1.39; hazard ratio, 0.54; 95% confidence interval, 0.31 to 0.93; and hazard ratio, 0.50; 95% confidence interval, 0.27 to 0.93, respectively). In the low-risk genotypes, higher urinary potassium excretion was associated with a higher risk of CKD progression (quartiles 2-4 versus 1: hazard ratio, 1.01; 95% confidence interval, 0.75 to 1.36; hazard ratio, 1.23; 95% confidence interval, 0.91 to 1.66; and hazard ratio, 1.53; 95% confidence interval, 1.12 to 2.09, respectively). We found no interaction between genotypes and urinary sodium excretion with CKD outcomes.

Conclusions: Higher urinary potassium excretion was associated with lower versus higher risk of CKD progression in high-risk and low-risk genotypes, respectively.