Hyperkalemia is a condition where potassium levels in your blood are too high. Normal serum potassium falls between 3.5 and 5.5 mEq/L, and hyperkalemia begins at anything above 5.5 mEq/L. Even a small increase beyond that range, less than 1.0 mEq/L, is linked to serious health risks because potassium plays a critical role in how your heart and muscles function.
Why Potassium Balance Matters
Potassium is one of the most important electrolytes in your body. It generates the electrical signals that make your heart beat and your muscles contract. This works because of a concentration difference: there’s far more potassium inside your cells than outside them. That gap creates a tiny electrical charge across every cell membrane, called the resting membrane potential, which sits around negative 90 millivolts in heart cells.
When extra potassium builds up in the blood, the gap between the inside and outside of cells shrinks. The resting charge shifts from negative 90 to something closer to negative 80 millivolts. At first, this actually makes cells easier to excite. But as levels climb higher, cells lose their ability to reset after firing, which is when dangerous heart rhythms and muscle weakness set in.
Severity Levels
Mild hyperkalemia (5.5 to 6.0 mEq/L) often produces no symptoms at all. It may respond to simple changes like reducing potassium in your diet or adjusting medications. Moderate hyperkalemia (6.0 to 6.5 mEq/L) needs prompt medical attention, though treatment depends on the full clinical picture. Severe hyperkalemia, above 6.5 mEq/L, is a medical emergency that typically requires aggressive intervention to prevent life-threatening heart problems.
Common Causes
Your kidneys handle about 90% of potassium removal from your body, so anything that impairs kidney function is the most common path to hyperkalemia. Chronic kidney disease and acute kidney injury both reduce the kidneys’ ability to filter potassium out of the blood, letting it accumulate.
Several widely used medications also raise potassium levels. ACE inhibitors and angiotensin receptor blockers, prescribed for high blood pressure and heart failure, reduce the hormonal signals that help your kidneys excrete potassium. Potassium-sparing diuretics like spironolactone do exactly what their name suggests. NSAIDs (common over-the-counter painkillers like ibuprofen) can impair kidney function enough to tip the balance. Potassium supplements themselves are another culprit, especially when combined with any of these other drugs.
Less common causes include severe tissue injury (burns, crush injuries, or massive blood cell breakdown), which releases large amounts of potassium from damaged cells into the bloodstream. Uncontrolled diabetes and severe metabolic acidosis can also shift potassium out of cells and into the blood.
Symptoms to Recognize
Mild hyperkalemia is frequently silent, which is part of what makes it dangerous. Many people discover it only through routine blood work. As potassium climbs higher, the neuromuscular and cardiac effects become more apparent.
Muscle-related symptoms include generalized weakness, fatigue, and in severe cases, flaccid paralysis where muscles simply stop responding. Deep tendon reflexes may become sluggish or disappear. Cardiac symptoms can include palpitations, lightheadedness, or fainting. At very high levels, the heart’s electrical system becomes so disrupted that fatal arrhythmias can occur without much warning.
How It Shows Up on an EKG
An electrocardiogram (EKG) is one of the first tools used to assess how hyperkalemia is affecting your heart, and the changes follow a predictable pattern as potassium rises. The earliest sign is tall, narrow, peaked T waves, the pointed bumps that represent the heart resetting between beats. This typically appears around 5.5 to 6.5 mEq/L.
At moderate levels (6.5 to 8.0 mEq/L), the electrical signal slows further. The PR interval, the pause between the upper and lower chambers firing, stretches out. P waves, which represent the upper chambers contracting, shrink or flatten. The QRS complex, representing the main heartbeat, starts to widen.
Above 8.0 mEq/L, P waves may vanish entirely. The QRS complex widens dramatically until the tracing takes on a smooth, rolling “sine wave” pattern. This is a pre-arrest rhythm. Without treatment, it can deteriorate into ventricular fibrillation or the heart stopping altogether.
False Positives: Pseudohyperkalemia
Not every high potassium result is real. Pseudohyperkalemia, a falsely elevated reading caused by problems with the blood sample itself, is surprisingly common. The most frequent cause is hemolysis, where red blood cells break open during or after the blood draw and release their potassium into the sample. Since red blood cells contain far more potassium than blood plasma, even a small amount of cell damage can skew the number significantly.
Several things during a routine blood draw can cause this. Pulling back too hard on a syringe, leaving a tourniquet on too long (guidelines recommend under one minute), pumping your fist repeatedly, or flipping the collection tube too vigorously can all rupture cells. Even cold weather plays a role: veins constrict in the cold, making draws harder and encouraging the very techniques that cause hemolysis. This phenomenon has been called “seasonal hyperkalemia” because false positives tend to spike in winter months.
If your potassium comes back unexpectedly high and you feel fine, your doctor will likely repeat the test with careful attention to blood draw technique before starting any treatment.
Emergency Treatment
When potassium is dangerously high or EKG changes are present, treatment follows a specific sequence designed to protect the heart first and lower potassium second.
The first step is an intravenous calcium solution, which stabilizes heart cell membranes within minutes. It doesn’t actually lower potassium levels. Instead, it counteracts potassium’s effect on the heart’s electrical system, buying time for other treatments to work. This alone can reduce the equivalent cardiac impact by 0.5 to 1.5 mEq/L.
Next, insulin (given with glucose to prevent low blood sugar) activates pumps on cell membranes that pull potassium back inside cells, temporarily lowering the amount circulating in the blood by 0.5 to 1.5 mEq/L depending on the dose. Inhaled medications that stimulate the same cellular pumps are sometimes used alongside insulin for an additive effect.
These measures are temporary. They shift potassium out of the bloodstream but don’t remove it from the body. For true removal, dialysis is the most effective option in severe cases, physically filtering excess potassium from the blood.
Long-Term Management
For people with chronic hyperkalemia, especially those with kidney disease, heart failure, or diabetes who need to stay on medications that raise potassium, newer oral potassium binders have become an important tool. These medications work in the gut, trapping potassium before it can be absorbed and carrying it out in your stool.
One type uses a compound with microscopic pores sized almost exactly to potassium ions, selectively capturing potassium while leaving sodium, calcium, and magnesium alone. Another uses a polymer that exchanges calcium for potassium in the colon, where free potassium concentrations are highest. Both have been studied in patients with kidney disease, diabetes, and heart failure, and they allow many people to continue taking otherwise beneficial heart and blood pressure medications that would otherwise need to be stopped.
Dietary changes also play a role in ongoing management. High-potassium foods include bananas, oranges, potatoes, tomatoes, and many salt substitutes (which replace sodium with potassium chloride). Working with a dietitian can help you identify where your biggest sources of dietary potassium are and find practical swaps that don’t require overhauling every meal.