Hyperkalemia is the medical term for having too much potassium in your blood. It’s defined as a serum potassium level greater than 5.0 mEq/L (milliequivalents per liter), with the normal range being 3.5 to 5.0 mEq/L. While mild elevations often cause no symptoms at all, levels above 6.5 mEq/L can become a medical emergency because of the way potassium controls your heartbeat.
What Potassium Does in Your Body
Potassium is one of the most important minerals for keeping your cells working. About 98% of the potassium in your body sits inside your cells, while only a tiny fraction circulates in your blood. This difference between inside and outside the cell creates an electrical charge across cell membranes, which is what allows your nerves to fire signals and your muscles (including your heart) to contract and relax in a coordinated rhythm.
A specialized pump on the surface of every cell constantly moves potassium inward and sodium outward to maintain this electrical balance. When blood potassium rises too high, that carefully maintained voltage changes. The cells that are most sensitive to this shift are heart muscle cells and nerve cells, which is why hyperkalemia’s most dangerous effects involve the heart.
How High Potassium Affects the Heart
As potassium levels climb, the electrical system of the heart changes in a predictable sequence. At levels above 5.5 mEq/L, the heart’s electrical recovery phase speeds up, which shows up on an ECG (heart tracing) as tall, pointed “tented” T waves. This is often the first detectable sign.
At levels above 6.5 mEq/L, more serious changes appear. The electrical signals that coordinate the upper and lower chambers of the heart slow down, causing the P waves on the ECG to flatten and disappear and the QRS complexes (which represent the main heartbeat) to widen. At around 10 mEq/L, the heart’s normal pacemaker can stop functioning entirely. The ECG develops a characteristic “sine wave” pattern, and cardiac arrest becomes imminent. This progression from subtle ECG changes to life-threatening rhythm problems is why hyperkalemia is treated as urgent once levels pass 6.0 mEq/L.
Symptoms and Why It’s Often Silent
Hyperkalemia rarely causes noticeable symptoms, which is why many people discover it only through a routine blood test. Most mild cases produce nothing you’d feel.
When symptoms do appear, mild hyperkalemia can cause abdominal pain, nausea, vomiting, or diarrhea. As levels rise higher, more concerning symptoms develop: muscle weakness or numbness in the arms and legs, heart palpitations, irregular heartbeat, and chest pain. Severe hyperkalemia can cause extreme muscle weakness, difficulty breathing, and symptoms resembling a heart attack.
Common Causes
The kidneys are responsible for removing excess potassium from the body, so kidney disease is the most common underlying cause. When the kidneys can’t filter potassium efficiently, levels build up in the blood. This includes both chronic kidney disease and acute kidney injury. People with diabetes-related kidney damage are particularly vulnerable because diabetes can also impair aldosterone, a hormone the kidneys need to excrete potassium properly.
Adrenal insufficiency (when the adrenal glands don’t produce enough hormones, including aldosterone) is another important cause. Without adequate aldosterone, the kidneys retain potassium even when kidney function itself is relatively normal.
Several common medications can raise potassium levels as well. Blood pressure drugs that block the renin-angiotensin-aldosterone system, including ACE inhibitors and ARBs, are frequent contributors. Potassium-sparing diuretics like spironolactone are another well-known culprit. Beta-blockers can also contribute by shifting potassium out of cells and into the bloodstream. People taking any of these medications, especially in combination or alongside kidney problems, typically need regular blood work to monitor potassium.
Other causes include severe dehydration, heart failure that reduces blood flow to the kidneys, and conditions that release large amounts of potassium from damaged cells (such as major burns, crush injuries, or widespread tissue breakdown).
False-Positive Results: Pseudohyperkalemia
Not every high potassium result on a blood test reflects what’s actually happening in your body. Pseudohyperkalemia, a falsely elevated reading, is surprisingly common. The most frequent cause is damage to red blood cells during the blood draw itself. When blood cells break open (a process called hemolysis), they release their internal potassium into the sample, artificially inflating the result.
This can happen if the phlebotomist uses too much suction with a syringe, leaves the tourniquet on too long, or if you pump your fist repeatedly during the draw. Even shaking the blood tube too vigorously or spinning the sample in a centrifuge more than once can produce a false reading. Cold weather can play a role too: harder-to-find veins lead to longer tourniquet times, and cold temperatures during transport can cause potassium to leak from cells in the sample. If a high result doesn’t match your clinical picture, your doctor will likely order a repeat draw with careful technique before diagnosing hyperkalemia.
How Hyperkalemia Is Treated
Treatment depends on how high the level is and whether ECG changes are present. For potassium under 6.0 mEq/L with no heart rhythm changes, treatment often involves addressing the underlying cause, adjusting medications, and making dietary changes. Potassium-binding medications taken by mouth can help pull excess potassium out of the body through the digestive tract.
For levels between 6.0 and 6.5 mEq/L, treatment in an acute setting typically involves intravenous insulin paired with glucose (the insulin drives potassium back into cells, and the glucose prevents blood sugar from dropping too low) plus inhaled albuterol, which also shifts potassium into cells. Diuretics may be added to help the kidneys flush potassium out faster.
Above 6.5 mEq/L, or whenever dangerous ECG changes are present, treatment becomes more aggressive. Intravenous calcium is given first because it stabilizes the heart’s electrical activity within minutes, buying time for other treatments to lower the actual potassium level. Dialysis may be needed if the kidneys can’t clear potassium on their own.
Managing Potassium Through Diet
For people with chronic kidney disease or recurring hyperkalemia, dietary potassium management becomes a daily consideration. The general guideline is to limit high-potassium foods, defined as those containing more than 200 mg of potassium per serving.
Some of the highest-potassium foods may surprise you. A baked potato with skin contains about 925 mg of potassium, and even French fries come in at around 675 mg. Sweet potatoes, white beans, lentils, and soybeans all pack 350 to 500 mg per serving. Among fruits, bananas (420 mg), prunes (350 mg per quarter cup), and pomegranate juice (355 mg per half cup) are among the highest. Cooked Swiss chard tops the vegetable list at 480 mg per half cup, followed by tomato sauce at 365 mg.
Two common kitchen items deserve special attention. Salt substitutes like Morton’s Lite Salt use potassium chloride instead of sodium chloride, making them potentially dangerous for anyone managing hyperkalemia (one serving contains about 690 mg of potassium). Processed foods with “potassium chloride” or “potassium phosphate” in the ingredients list are also worth avoiding. Coconut water and electrolyte drinks, often marketed as healthy, contain around 240 to 280 mg of potassium per serving and can contribute to elevated levels in people with impaired kidney function.
Lower-potassium alternatives exist in every food category. Choosing apples instead of bananas, white rice instead of quinoa, and iceberg lettuce instead of cooked spinach can significantly reduce daily potassium intake without requiring dramatic changes to your eating patterns.