High potassium, called hyperkalemia, happens when your blood potassium rises above 5.0 mEq/L. Normal levels sit between 3.5 and 5.0 mEq/L. The most common causes are kidney problems, certain medications, and conditions that push potassium out of your cells and into your bloodstream. But sometimes, a high reading isn’t real at all: it can be a lab error from the way your blood was drawn.
How Your Body Normally Controls Potassium
Your kidneys do the heavy lifting. They filter excess potassium out of your blood and send it into your urine. A hormone called aldosterone, produced by your adrenal glands, drives this process. Aldosterone signals your kidneys to absorb sodium and, in exchange, push potassium out. It also activates pumps on kidney cells that keep this exchange running efficiently. When any part of this system breaks down, potassium accumulates.
Inside your body, most potassium (about 98%) is stored within your cells, not floating in your blood. Insulin and the normal acid-base balance of your blood help keep potassium tucked inside cells. Anything that disrupts insulin levels or makes your blood more acidic can release a flood of potassium into your bloodstream, even if your total body potassium hasn’t changed.
Kidney Disease Is the Most Common Cause
Your kidneys are responsible for excreting roughly 90% of the potassium you take in. When they lose function, potassium builds up. In chronic kidney disease, the risk climbs as kidney function declines. A large U.S. study found that the incidence of hyperkalemia in people with non-dialysis chronic kidney disease was about 3.4 events per 100 person-years overall, but rates jumped dramatically in advanced stages, reaching up to 19.1 events per 100 person-years in patients with the most severe kidney damage.
Acute kidney injury, where your kidneys stop working suddenly due to dehydration, infection, or a drug reaction, can cause potassium to spike quickly because the kidneys simply can’t filter it out fast enough.
Medications That Raise Potassium
Several widely prescribed drugs interfere with potassium excretion. The biggest culprits are medications used to treat high blood pressure and heart failure:
- ACE inhibitors and ARBs. These block the hormone system (renin-angiotensin-aldosterone) that tells your kidneys to excrete potassium. ACE inhibitors carry the strongest association with hyperkalemia among blood pressure drugs.
- Potassium-sparing diuretics. Unlike most water pills, these reduce how much potassium your kidneys release. Aldosterone-blocking drugs fall into this category.
- Beta-blockers. Often overlooked as a cause, these are associated with a 13% increased risk of hyperkalemia.
- NSAIDs. Common anti-inflammatory painkillers can reduce blood flow to the kidneys and lower aldosterone production, slowing potassium excretion.
The risk multiplies when you take more than one of these at the same time, or if you already have reduced kidney function. Potassium supplements and potassium-based salt substitutes add to the problem. A single medium baked potato with skin contains 926 mg of potassium. If your kidneys or medications already limit your ability to clear potassium, even normal dietary intake can push levels too high.
Conditions That Shift Potassium Out of Cells
Even with healthy kidneys, potassium can surge in your bloodstream if something forces it out of your cells. This is called a transcellular shift, and a few situations trigger it.
Diabetic ketoacidosis (DKA) is a classic example. When insulin is severely lacking, potassium has no signal to stay inside cells. The acidic blood that develops in DKA makes things worse: as excess acid enters cells to be buffered, potassium moves out to maintain electrical balance. Research has shown that the high potassium seen in DKA is more closely tied to the insulin deficiency and high blood sugar concentration than to the acidity itself.
Metabolic acidosis from other causes works the same way. An older estimate suggested that potassium rises by about 0.6 mEq/L for every 0.1-unit drop in blood pH, though the actual range varies widely from person to person (0.2 to 1.7 mEq/L).
Severe tissue damage, such as major burns, crush injuries, or the breakdown of muscle tissue (rhabdomyolysis), physically releases the potassium stored inside cells into the bloodstream all at once.
Adrenal Gland Problems
Your adrenal glands sit on top of your kidneys and produce aldosterone, the hormone that tells your kidneys to get rid of potassium. In Addison’s disease, also called primary adrenal insufficiency, the adrenal glands are damaged and can’t produce enough aldosterone or cortisol. Without aldosterone, your kidneys hold on to potassium instead of excreting it. According to the National Institute of Diabetes and Digestive and Kidney Diseases, severe adrenal insufficiency can cause life-threatening high potassium along with dangerously low blood pressure and blood sugar.
When the Lab Result Is Wrong
A surprisingly common cause of a high potassium reading is pseudohyperkalemia: your potassium is actually normal, but the lab result says otherwise. This happens when potassium leaks out of blood cells in the sample tube, not in your body. Common triggers include drawing blood with too much vacuum or through a needle that’s too small, leaving a tourniquet on too long, clenching your fist repeatedly during the blood draw, or delays in processing the sample. People with very high platelet or white blood cell counts can also get false readings as potassium leaks from those cells after collection.
If your potassium comes back high but you feel fine and have no obvious risk factors, your doctor will typically repeat the test with careful technique before assuming the result is real.
Symptoms and Warning Signs
Mild hyperkalemia (5.5 to 6.0 mEq/L) often causes no symptoms at all, which is part of what makes it dangerous. As levels climb into the moderate range (6.1 to 7.0 mEq/L), you may notice muscle weakness, fatigue, numbness, or tingling. Some people experience nausea.
The real danger is to your heart. Potassium controls the electrical signals that keep your heart beating in rhythm. At levels above 6.0 mEq/L, changes start appearing on an electrocardiogram, beginning with tall, peaked T waves. As potassium continues to rise, the heartbeat can slow, electrical signals can become delayed or blocked, and the pattern on the monitor widens and distorts. Above 9.0 mEq/L, the heart rhythm can deteriorate into a pattern that looks like a sine wave, which is a pre-terminal rhythm that can progress to cardiac arrest.
Severe hyperkalemia (7.0 mEq/L and above) is a medical emergency. Treatment focuses first on protecting the heart with intravenous calcium, which stabilizes the heart’s electrical activity within minutes. Additional treatments then work to push potassium back into cells and remove excess potassium from the body.
Who Is Most at Risk
Several factors stack together to raise your odds. You’re at the highest risk if you have chronic kidney disease and take one or more of the medications listed above. Uncontrolled diabetes adds another layer, both because of the insulin-related shifts and because diabetes is a leading cause of kidney damage. Older adults are more vulnerable because kidney function naturally declines with age, and they’re more likely to be on multiple medications that affect potassium.
People with heart failure face a particularly difficult balance. The medications that best protect the heart in heart failure, like ACE inhibitors and aldosterone blockers, are the same ones that raise potassium. For these patients, regular blood monitoring is essential to catch rising levels before they become dangerous.