Potassium is a mineral that every cell relies on. It helps nerves fire, muscles contract and the heart keep a steady rhythm. The kidneys hold blood levels in a narrow range, which is why potassium is checked on routine blood work and why it gets extra attention in kidney disease and in people taking blood pressure medicines.

Normal levels and what you need

According to the National Kidney Foundation, blood potassium for most healthy people should be between 3.5 and 5.0, depending on the lab. Above 5.0 is usually considered high (hyperkalemia) and below 3.5 is low (hypokalemia).

Most of us take in potassium through food. The NIH Office of Dietary Supplements sets an adequate intake of 3,400 mg a day for men and 2,600 mg for women, and lists good sources including dried apricots, prunes, raisins, orange juice, bananas, potatoes, squash, spinach, tomatoes, broccoli, lentils, beans, nuts, milk, yogurt, meat and fish. Our article on banana nutrition covers one familiar source.

When potassium is too high

High potassium is most often a kidney story. The NIH lists chronic kidney disease, type 1 diabetes, heart failure, liver disease and adrenal insufficiency among the conditions that raise the risk. Common medicines can push it up too, including ACE inhibitors and potassium-sparing diuretics. Potassium supplements and potassium-based salt substitutes can cause problems when the kidneys cannot clear the extra.

Many people feel nothing. The National Kidney Foundation says symptoms, when they occur, are often vague, such as muscle weakness, numbness, tingling or nausea, and usually appear above 6.0. How fast the level rises can matter more than the number itself. Severe or sudden hyperkalemia can cause palpitations, shortness of breath, chest pain and dangerous heart rhythms.

Treatment depends on the cause and the level. The National Kidney Foundation describes potassium binders (powders that remove extra potassium through the gut), diuretics, a medication review and, when levels stay high, a lower-potassium diet planned with a kidney dietitian. NKF still encourages fruits and vegetables, chosen with care. The 2024 KDIGO guideline notes that high potassium on an ACE inhibitor or ARB can often be managed with these measures rather than stopping a medicine that protects the kidneys. For people with stage 3 to 5 CKD and a history of high potassium, KDIGO suggests limiting foods rich in absorbable potassium, such as processed foods.

When potassium is too low

Low potassium usually reflects losses. The NIH and MedlinePlus list the common causes:

  • Diuretics (water pills), especially thiazide and loop types
  • Prolonged vomiting or diarrhea
  • Heavy sweating
  • Laxative overuse
  • Adrenal conditions, including aldosteronism
  • Alcohol use disorder

Mild low potassium can cause constipation, tiredness and muscle weakness. The NIH notes that severe hypokalemia can cause paralysis, trouble breathing and an irregular heartbeat, and can be life-threatening. Magnesium is often checked at the same time; our article on magnesium levels explains that mineral.

Unexplained low potassium in someone with high blood pressure can be a clue to primary aldosteronism, a hormone cause of hypertension. The 2025 AHA/ACC blood pressure guideline lists hypertension with low potassium, whether spontaneous or caused by a diuretic, among the reasons to screen for it.

When the number is not what it seems

A single high result is not always real. MedlinePlus notes that clenching and relaxing your fist just before or during a blood draw can temporarily raise the level and give an incorrect result. KDIGO also asks clinicians to be aware of variation between serum and plasma samples, time of day and season. If a high result does not fit the picture, a careful repeat test is often the next step. MedlinePlus also notes that natural black licorice can lower potassium.

Before you change your diet or medicines on the strength of one result, talk it through with your doctor. The answer depends on your kidney function, your medicines and the trend.

When to seek care

Call your doctor about any potassium result outside the normal range, and before taking potassium supplements or salt substitutes if you have kidney disease or take an ACE inhibitor, ARB or potassium-sparing diuretic. The National Kidney Foundation calls sudden or severe hyperkalemia a life-threatening condition that needs immediate care: call 911 for palpitations, chest pain, severe weakness or shortness of breath.

Dr. Yana Shtern is board-certified in Internal Medicine and Nephrology, and labs are drawn in our office, so a potassium result can be repeated and acted on quickly. Our kidney care page explains the practice’s approach. If you have had a potassium result you would like explained, a complimentary meet and greet with Dr. Shtern is a good place to begin.

This article is general information, not advice for your situation. Members can call the office with questions about their own care.