Serum Potassium Level Varies by Race in Recent Observational Study

Potassium is essential for maintaining normal neuromuscular functioning, preserving fluid volumes in cells, and regulating blood pH. Out of normal range potassium levels are associated with an increased risk of all-cause and cardiovascular mortality, and cardiac arrhythmias and end-stage renal disease (ESRD).

Recent studies have found that serum potassium levels are, on average, lower in African Americans compared with European Americans. Possible explanations for the difference include lower intake of dietary potassium among African Americans compared with European Americans. However, according to Yan Chen, MHS, and colleagues, racial differences in other factors that influence potassium levels may also be in play, including medication use and comorbid conditions. Biologic differences by ethnicity may also have a role in the difference.

The researchers conducted an observational study to examine the association of race with serum potassium level using data from two cohorts: the Racial and Cardiovascular Risk Anomalies in Chronic Kidney Disease (CKD) (RCAV) Study and the population-based Atherosclerosis Risk in Communities (ARIC) study. The current study was designed to examine potential explanatory factors in the cross-sectional association between levels of serum potassium and race in the RCAV cohort, and in order to assess the evidence for a genetic component, the association between percent African ancestry and serum potassium level among African Americans in the ARIC Study. Results of the current study were reported in the American Journal of Kidney Diseases [2017;70(2):244-251].

There were 2,662,462 participants in the RCAV study population. Mean age was 62 years, 18.0% (n=470,985) were African American, and 6.3% (n=167,995) were women. Mean serum potassium level was 4.2 mmol/L and mean estimated glomerular filtration rate (eGFR) was 80 mL/min/1.73 m2.

Compared with other non–African Americans, African Americans were younger, more likely to be women, and had slightly higher blood pressures and history of hypertension but lower history of cardiovascular disease. Among African Americans, serum potassium levels were lower, with a greater proportion of potassium levels <3.5 mmol/L, compared with non–African Americans (5.4% vs 2.2%; P<.001), and a smaller proportion of potassium levels >5.5 mmol/L (0.35% vs 0.62%; P<.001). There were similar patterns in the ARIC data.

In results of cross-sectional analyses of potassium levels and race in the RCAV cohort, the difference between serum potassium levels in African Americans versus non–African Americans was  –0.162 (95% confidence interval [CI], –0.164 to –0.161) mmol/L on average. Following progressive adjustment for potential confounders (demographics, comorbid conditions, and potassium-altering medication use), the association was attenuated but remained significant.

There were similar associations with race when potassium level was categorized as a binary variable reflecting hypo- or hyperkalemia. In all unadjusted and progressively adjusted models, African Americans had higher risk for hypokalemia and lower risk for hyperkalemia compared with non–African Americans. In the fully adjusted model, the odds ratios for hypokalemia and hyperkalemia were 0.59 (95% CI, 0.58-0.60) and 0.62 (95% CI, 0.59-0.66), respectively.

In the ARIC study, there were 3450 African Americans available for genetic analysis. Mean age was 53.5 years, and mean serum potassium level was 4.19 mmol/L. Median African ancestry was 84.8%. In unadjusted analysis, there was a significant association between each additional 10% of African ancestry and a –0.0265 (95% CI, –0.0412 to –0.0109) mmol/L difference in serum potassium levels. In all models, the association persisted.

In both race groups, the risk for mortality was similar; higher and lower serum potassium levels were associated with increased risk for mortality. The mortality risk associated with lower potassium levels was lower in African Americans versus non–African Americans; mortality risk associated with higher potassium levels was slightly greater. There was no difference by race in risk relationship between potassium and ESRD.

Study limitations cited by the authors were the lack of data for potassium intake or urinary potassium excretion, differences in ancestry-information markers among African American subgroups, and the small percentage of women in the database.

“In summary, we found that African Americans had lower serum potassium levels than non–African Americans in two large cohorts, and we demonstrated that greater percent of African ancestry was associated with lower serum potassium levels. Both hypo- and hyperkalemia were risk factors in hyperkalemia and slightly lower risk in hypokalemia compared with non–African Americans. Contrary to previous studies, these results suggest that potassium monitoring may require even greater vigilance among African Americans, particularly when prescribed potassium-wasting medication,” the researchers said.

Takeaway Points

  1. Researchers conducted an observational study utilizing data from two large cohort studies to investigate associations between race and levels of serum potassium as well as the interaction of race and potassium levels with outcomes.
  2. In the first cohort (RCAV study), on average, following adjustment for potential confounders, potassium levels among African Americans were 0.162 mmol/L lower in African Americans compared with non–African Americans.
  3. In the second cohort (ARIC study), higher percentage of African ancestry was related to lower potassium levels (–0.027 mmol/L per 10% African ancestry).