Potassium · low result
Low potassium (hypokalemia): what it means, causes, symptoms and how it is treated
Short answer
Low potassium (hypokalemia) — below about 3.5 mmol/L — most often follows losses: diuretics, vomiting, diarrhea, laxative use or heavy sweating, or low intake with alcohol use or an eating disorder. Less common causes are high aldosterone (often with high blood pressure), Cushing's syndrome, inhaled or oral steroids, high-dose insulin, and magnesium deficiency — which matters because potassium will not correct until magnesium is replaced. Mild hypokalemia (3.0–3.4) usually causes cramps and fatigue at most and is corrected with diet, supplements and fixing the cause; below about 3.0, or any low value with palpitations or marked weakness, needs same-day attention because of the heart rhythm.
Medically reviewed by Youmna DiStefano, MD · Last reviewed November 2026
When does this result need same-day care?
- Potassium below 2.5–3.0 mmol/L, or any low value with palpitations, an irregular pulse, severe weakness or trouble breathing — same-day or emergency care
- Low potassium in someone taking digoxin or with known heart disease, or after a prolonged vomiting or diarrheal illness with dizziness — same-day care
- Sudden severe weakness or inability to move the limbs — emergency care (periodic paralysis)
What is the normal range for Potassium?
- age 18+: 3.50 – 5.00 mmol/L
Can reflect diuretic use, GI losses, or low intake.
Full reference table, citations and testing options: Potassium biomarker page.
What are the common causes of low Potassium?
- Diuretics — thiazides and loop diuretics (furosemide, bumetanide); the most common cause in treated hypertension and heart failure
- Gastrointestinal losses — vomiting, diarrhea, laxative use or abuse, ostomies, villous adenomas
- Low intake — alcohol use disorder, eating disorders, very restricted diets; usually combined with losses
- Magnesium deficiency — from diuretics, alcohol, proton-pump inhibitors, malabsorption; potassium cannot be held until magnesium is corrected
- Primary hyperaldosteronism — an aldosterone-producing adrenal adenoma or hyperplasia; low potassium with high blood pressure is the classic clue, and it is more common than once thought
- Cushing's syndrome and high-dose corticosteroids; licorice and some chewing tobaccos (glycyrrhizin), which mimic aldosterone
- Shifts into cells — insulin (especially high doses or refeeding), beta-agonist inhalers, theophylline, alkalosis, and rare periodic paralysis (including with hyperthyroidism)
- Kidney causes — renal tubular acidosis, Bartter and Gitelman syndromes, high-dose penicillins, amphotericin, cisplatin
What symptoms go with low Potassium?
- Muscle cramps, weakness and aches, especially in the legs
- Fatigue, constipation, bloating
- Palpitations and an irregular heartbeat
- Frequent urination and thirst when chronic (the kidneys lose concentrating ability)
- Paralysis, breathing difficulty and dangerous arrhythmias when very low
What do clinicians usually check next?
- Magnesium — deficiency blocks correction and must be replaced first
- Blood pressure, and aldosterone and renin when potassium is low with high blood pressure, or low without an obvious loss
- Review diuretics, laxatives, inhalers, steroids, licorice and alcohol; a frank history of vomiting or purging
- Bicarbonate (CO2) and a metabolic panel — alkalosis points to vomiting or diuretics, acidosis to diarrhea or renal tubular acidosis
- Urine potassium (spot or 24-hour) to tell kidney losses from gut losses when the cause is unclear
- An ECG when potassium is below about 3.0 mmol/L, with symptoms, or in anyone on digoxin or with heart disease
- Replacement — dietary potassium and oral potassium chloride for mild cases, intravenous in hospital for severe; recheck within days, then treat the cause so it does not recur
Follow-up tests available at TestWell: Magnesium Test ($18.99), Aldosterone Test ($61.99).
How do you recheck Potassium?
Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.
| Test or panel | Type | Price | Fasting | Results |
|---|---|---|---|---|
| Basic Metabolic Panel | Test · 8 biomarkers | $17.99 | Yes | 1–3 business days |
Common questions
Can I fix low potassium with bananas?
Diet helps mild cases, but the cause matters more — and low magnesium must be corrected first or potassium won't hold. Values below 3.0 need a clinician.
What is a low potassium level?
Below the lab's lower limit, usually 3.5 mmol/L. 3.0–3.4 is mild, 2.5–2.9 moderate, and below 2.5 severe. The heart is the organ at risk, so symptoms and any heart disease or digoxin use matter as much as the number.
What causes low potassium?
Losing it — diuretics, vomiting, diarrhea, laxatives, sweating — or not taking enough in with alcohol or restricted eating. Low magnesium often travels with it. High aldosterone, Cushing's, steroids, insulin and inhalers are the less common causes, and hyperaldosteronism is the one not to miss in someone with high blood pressure.
What are the symptoms of low potassium?
Muscle cramps and weakness, fatigue and constipation are the common ones; palpitations and an irregular heartbeat mean it needs attention now. Mild hypokalemia often has no symptoms and is found on a routine panel.
Why does my potassium keep dropping even with supplements?
Check magnesium — if it is low, potassium will not stay up until magnesium is replaced. The other explanations are an ongoing loss that has not been addressed (a diuretic, laxatives, vomiting) or an aldosterone excess, which is worth testing for if you also have high blood pressure.
How is low potassium treated?
Mild: potassium-rich foods (potatoes, beans, spinach, bananas, oranges, yogurt) and oral potassium chloride, with magnesium if low, and a fix for the cause — often a diuretic change or adding a potassium-sparing agent. Severe or symptomatic hypokalemia is treated in hospital with monitored intravenous potassium.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.