Urinary sodium/chloride excretion vital in diagnosis, treatment of chronic hypokalemia
To make an accurate diagnosis and treatment plan for patients with chronic normotensive hypokalemia, it is important to include an integrated interpretation of the urine sodium (Na+) and chloride (Cl−) excretion and their ratio apart from body mass index (BMI), sex and blood acid-base status, suggests a recent study.
Researchers identified clinical and laboratory parameters helpful for differentiating the causes of chronic hypokalemia by prospectively enrolling normotensive patients (n=99; serum potassium [K+], 2.8 mmol/L; duration 4.1 years) referred to a tertiary academic medical centre over 5 years. They determined clinical features and laboratory examinations, including blood and spot urine electrolytes, acid-base status, biochemistries and hormones.
The most common complaints were neuromuscular symptoms. The predominant renal tubular disorders were Gitelman syndrome (n=33), Bartter syndrome (n=10) and distal renal tubular acidosis (n=12), but 44 patients were diagnosed with anorexia/bulimia nervosa (n=21), surreptitious use of laxatives (n=11) or diuretics (n=12). Patients with gastrointestinal causes and surreptitious diuretics use were predominantly female, had lower BMI and less K+ supplementation.
All patients with renal tubular disorders had high urine K+ excretion (transtubular potassium gradient >3; urine K+/Cr >2 mmol/mmol), which was also found in >50 percent of patients with gastrointestinal causes.
Urine Na+ and Cl− excretions were high and coupled (urine Na+/Cl− ratio ∼1) in renal tubular disorders and “on” diuretics use, whereas skewed or uncoupled urine Na+ and Cl− excretions were observed in anorexia/bulimia nervosa and laxatives abuse (urine Na+/Cl− ratio, 5.0 and 0.4, respectively) and low urine Na+ and Cl− excretions with fixed Na+/Cl− ratios (0.9) when “off” diuretics.
The findings suggest that integrated interpretation of Na+/Cl− excretion and ratio is critical in correctly diagnosing chronic hypokalemia with K+ wasting from the kidneys or gut.