Can Diarrhea Cause Hyperkalemia?
No, diarrhea typically causes hypokalemia (low potassium), not hyperkalemia. Diarrhea leads to excessive gastrointestinal potassium losses, resulting in potassium depletion and low serum levels 1, 2, 3.
Mechanism of Potassium Loss in Diarrhea
Diarrhea increases fecal potassium excretion through multiple mechanisms: unabsorbed anions that obligate potassium loss, electrochemical gradients from active chloride secretion, and secondary hyperaldosteronism 3.
Normal fecal potassium excretion is only 9 mEq/day, but this increases substantially during diarrheal illness as the intestinal absorptive capacity is overwhelmed 3.
The small intestine normally absorbs 90% of dietary potassium intake (approximately 81 mEq/day from a 90 mEq/day diet), but diarrhea disrupts this absorption while simultaneously increasing losses 3.
Clinical Manifestations of Diarrhea-Related Hypokalemia
Neuromuscular manifestations are common, including neck flop (100% of cases), diminished bowel sounds (82.6%), truncal weakness (52.2%), limb weakness (52.2%), and in severe cases, flaccid paralysis 4.
Young malnourished children are at highest risk, particularly those rehydrated with solutions inadequate in potassium, with severity correlating with stool frequency, degree of dehydration, and nutritional status 4.
Cardiac arrhythmias can develop as a consequence of hypokalemia from chronic or frequent diarrhea 2.
The Rare Exception: BRASH Syndrome
Diarrhea can paradoxically trigger hyperkalemia in patients on specific medications through BRASH syndrome (Bradycardia, Renal failure, AV-nodal blockade, Shock, Hyperkalemia) 5.
BRASH syndrome occurs when diarrhea-induced hypovolemia triggers acute kidney injury in patients taking renin-angiotensin-aldosterone system (RAAS) inhibitors, beta-blockers, and potassium-sparing diuretics 5.
The mechanism involves a vicious cycle: diarrhea causes volume depletion → acute renal failure → hyperkalemia → bradycardia (exacerbated by beta-blockers/calcium channel blockers) → hypotension → worsening renal perfusion → further hyperkalemia 5.
A case report documented a 92-year-old man on amlodipine, benazepril, metoprolol, furosemide, and spironolactone who developed severe hyperkalemia (7.3 mmol/L) and bradycardia (26 bpm) following diarrhea 5.
Critical Clinical Context
Primary adrenal insufficiency can present with diarrhea AND hyperkalemia, but this represents a distinct pathophysiology (aldosterone deficiency) rather than diarrhea causing hyperkalemia 1.
Surreptitious ingestion of potassium-sparing diuretics can cause the unusual combination of chronic diarrhea with hyperkalemia, as diuretics decrease sodium absorption in the intestine while blocking mineralocorticoid receptors 6.
In patients with severe vomiting accompanying diarrhea, hypokalaemia and alkalosis may be present rather than hyperkalemia, even in conditions like adrenal insufficiency where hyperkalemia would otherwise be expected 1.
Key Clinical Pitfall
Do not assume diarrhea alone causes hyperkalemia—if hyperkalemia is present with diarrhea, aggressively search for: medications (RAAS inhibitors, potassium-sparing diuretics, NSAIDs), acute kidney injury, adrenal insufficiency, or surreptitious drug ingestion 1, 7, 6, 5.