Laboratory Results in Hypoaldosteronism
Hypoaldosteronism characteristically presents with hyperkalemia (>94% of cases), often accompanied by hyponatremia (54.5% of cases) and metabolic acidosis (60.3% of cases), with low plasma aldosterone and low or inappropriately normal plasma renin activity. 1
Core Laboratory Abnormalities
Electrolyte Disturbances
- Hyperkalemia is the hallmark finding, present in 94.6% of cases, with mean serum potassium of 5.4 ± 0.5 mmol/L 1
- Hyponatremia occurs in approximately 54.5% of cases (mean serum sodium: 132.1 ± 6.3 mmol/L), particularly hypovolemic hyponatremia due to urinary sodium wasting 1
- Hyperchloremic metabolic acidosis is present in 60.3% of cases (mean serum bicarbonate: 22.6 ± 3.3 mmol/L) due to impaired H+ excretion in the distal nephron 1, 2
Hormonal Profile
- Low plasma aldosterone concentration is the defining feature, with baseline levels typically ranging from 5.4 to 21.6 ng/dL 3
- Suppressed plasma renin activity (0.12 to 1.3 ng/mL/hr) is characteristic of the most common form—hyporeninemic hypoaldosteronism—occurring in approximately 70% of adult cases 4, 3
- Normal cortisol reserve distinguishes isolated hypoaldosteronism from primary adrenal insufficiency, which occurs in only 5% of hypoaldosteronism cases 1, 3
Diagnostic Approach
Key Distinguishing Features
- The stimulated plasma aldosterone/serum potassium ratio below 3 is highly useful for diagnosis, as stimulated aldosterone reflects bioactivity on the collecting tubule 4
- Unlike primary aldosteronism where plasma aldosterone should be at least 10-15 ng/dL for a positive test 5, hypoaldosteronism shows inappropriately low aldosterone relative to the elevated potassium
- Urinary electrolyte patterns show increased urinary sodium excretion (sodium wasting) and decreased urinary potassium excretion 1, 2
Clinical Context
- Patients are typically older (median age 77 years, often >50 years) with diabetes mellitus and/or nephropathy 1, 3
- Mild to moderate renal insufficiency is common and contributes to the severity of hyperkalemia and acidosis 2, 3
- Hypovolemia, when present, is associated with more florid clinical presentation and more severe hyponatremia 1
Important Caveats
- Do not rely on hyperkalemia alone: While present in >94% of cases, approximately 25% of patients may have normokalemia at presentation 4
- Hyponatremia is not universal: Only about half of patients demonstrate sodium depletion, so its absence does not exclude the diagnosis 1, 4
- Consider medication effects: Prostaglandin inhibitors, beta-blockers, ACE inhibitors, and potassium-sparing diuretics can contribute to or mimic hypoaldosteronism 2
- Exclude primary adrenal insufficiency: Check cortisol reserve and ACTH levels, as the combination of hyponatremia and hyperkalemia occurs in only about 50% of primary adrenal insufficiency cases at diagnosis 6