A high potassium level, or hyperkalemia, is a medical condition defined as a potassium concentration in the blood serum that is above the normal range (typically greater than 5.0 to 5.5 mEq/L). To understand why this is dangerous, it is essential to understand potassium’s role as the body’s primary intracellular electrolyte.

Over 98% of the potassium in your body is stored inside your cells, while only a tiny fraction circulates in your bloodstream. This massive difference in concentration between the inside and outside of cells creates a critical electrical gradient across the cell membrane.

• A helpful analogy is to think of your nerve and muscle cells as tiny, rechargeable batteries. This electrical gradient is what gives the battery its “charge,” keeping it in a ready state, prepared to fire an impulse.
• In hyperkalemia, the potassium concentration outside the cells (in the blood) becomes too high.
• This disrupts the normal electrical balance, effectively “short-circuiting” the battery. It lowers the resting electrical potential, making the nerve and muscle cells irritable, over-excitable, and unable to repolarize or “reset” properly after firing.

This electrical instability is most dangerous for heart muscle cells. An irritable heart that cannot reset properly is prone to developing chaotic, life-threatening rhythms, which can lead to sudden cardiac arrest.

In my experience, hyperkalemia often shows up during routine blood work, but in serious cases, it can lead to dangerous heart rhythm problems if untreated.

The level of potassium in the blood is a tight balance between intake (from food), excretion (primarily by the kidneys), and the distribution of potassium between the inside and outside of cells. Hyperkalemia occurs when this balance is severely disrupted.

There are three main mechanisms that can cause a high potassium level:

1. Decreased Excretion by the Kidneys: This is, by far, the most common cause of persistent hyperkalemia. The kidneys are the primary regulators of potassium, and if they are not functioning properly, they cannot excrete enough potassium into the urine to keep the blood level normal.
2. Shift of Potassium Out of Cells: A large amount of potassium can rapidly shift from inside the cells out into the bloodstream. This can overwhelm the kidneys’ ability to excrete it quickly enough, causing a temporary but dangerous spike in the blood potassium level.
3. Excessive Intake: This is a very rare cause of hyperkalemia in a person with normal kidney function, as healthy kidneys are very efficient at excreting excess potassium. However, for a person with kidney disease, consuming high-potassium foods or supplements can be very dangerous.

Patients often assume it’s from eating too many bananas. But I explain that in healthy people, the kidneys easily regulate potassium from food.

A person develops hyperkalemia due to an underlying disease or as a side effect of certain medications that interfere with the body’s ability to regulate potassium.

The most common and important causes and risk factors include:

• Chronic Kidney Disease (CKD) and Acute Kidney Injury (AKI): This is the single greatest risk factor. As kidney function declines, the body’s ability to excrete potassium in the urine is progressively impaired. Patients with advanced CKD or those on dialysis are at very high risk.
• Medications: Several very common medications are known to raise potassium levels, particularly in patients with even mild kidney dysfunction. The risk is significantly increased when these drugs are used in combination. Key medications include:
  • ACE Inhibitors (e.g., lisinopril, ramipril) and Angiotensin II Receptor Blockers (ARBs) (e.g., losartan, valsartan), which are widely used for high blood pressure and diabetes.
  • Potassium-Sparing Diuretics, like spironolactone and amiloride.
  • Nonsteroidal Anti-inflammatory Drugs (NSAIDs), such as ibuprofen and naproxen.
• Addison’s Disease (Primary Adrenal Insufficiency): A rare condition where the adrenal glands do not produce enough of the hormone aldosterone. Aldosterone is essential for signaling the kidneys to excrete potassium.
• Massive Tissue Destruction: Conditions that cause the rapid death of a large number of cells can release a massive amount of intracellular potassium into the bloodstream. This includes severe trauma, crush injuries, major burns, or a condition called rhabdomyolysis (massive muscle breakdown).
• Poorly Controlled Diabetes: A lack of insulin impairs the body’s ability to move potassium into cells. In a state of high blood sugar and acidosis (like diabetic ketoacidosis), potassium can move out of cells into the blood.

Clinically, I most often see it in patients with kidney failure, use of potassium-sparing diuretics, ACE inhibitors, or after significant tissue breakdown.

One of the most dangerous aspects of hyperkalemia is that it is often a “silent” condition. Mild to moderate hyperkalemia frequently causes no noticeable symptoms at all. It is often discovered incidentally on a routine blood test performed for another reason.

When symptoms do occur, it is usually because the potassium level is severely high and is beginning to have a significant effect on nerve and muscle function. These symptoms can include:

• Muscle weakness or fatigue.
• Numbness or tingling sensations (paresthesias).
• Nausea and vomiting.
• Heart palpitations or an unusually slow or irregular heartbeat.
• In very severe cases, the muscle weakness can progress to a flaccid paralysis, and the heart rhythm can deteriorate into cardiac arrest. Often, a fatal arrhythmia is the first and only symptom of severe hyperkalemia.

Patients may report muscle weakness, fatigue, or palpitations but sometimes there are no symptoms until life-threatening arrhythmias occur.

A diagnosis of hyperkalemia is made in a clinical setting and requires an urgent evaluation to assess its severity and effect on the heart.

• Blood Test: The diagnosis is made with a basic metabolic panel (BMP) or an electrolyte panel, which are simple blood tests that measure the serum potassium level. A result above the normal laboratory range (e.g., >5.0 or 5.5 mEq/L) confirms the diagnosis.
• Ruling Out Pseudohyperkalemia: Sometimes, a blood sample can be hemolyzed (the red blood cells can break) during a difficult blood draw, which releases potassium into the sample and creates a falsely high reading. A doctor will often repeat the test on a carefully drawn sample if pseudohyperkalemia is suspected.

The Immediate Next Step: An Electrocardiogram (ECG or EKG)

A diagnosis of moderate to severe hyperkalemia is a medical emergency requiring an immediate ECG. This is to check the effects of high potassium on the heart’s electrical conduction system. The ECG shows a characteristic, progressive series of changes as the potassium level rises:

• Tall, “peaked” T-waves.
• A widening of the QRS complex.
• Eventually, the ECG trace can degenerate into a “sine wave” pattern, which often precedes ventricular fibrillation or cardiac arrest.

The diagnostic workup will also include a thorough review of the patient’s medications and tests of their kidney function to determine the underlying cause.

Clinically, I confirm it with serum potassium levels and often repeat the test to rule out false elevation from sample hemolysis.

Moderate to severe hyperkalemia is a life-threatening medical emergency that requires immediate treatment in a hospital. The goals of treatment are to protect the heart from arrhythmias, to temporarily shift potassium back into the cells, and to definitively remove the excess potassium from the body.

The emergency treatment follows a well-defined, three-step algorithm:

1. Stabilize the Heart Muscle

This is the first and most urgent step if there are any ECG changes.

• Intravenous (IV) Calcium Gluconate: A doctor will immediately administer IV calcium. It is crucial to understand that calcium does not lower the potassium level. Instead, it acts like a “shield,” stabilizing the cardiac cell membrane and protecting the heart from the dangerous electrical effects of the high potassium, thereby preventing a fatal arrhythmia.

2. Shift Potassium into the Cells

These are temporary measures to quickly lower the blood potassium level by moving it back inside the cells.

• IV Insulin and Glucose: Insulin is the most powerful and effective agent for shifting potassium into cells. Glucose is given at the same time to prevent the patient’s blood sugar from dropping too low.
• Beta-2 Agonists: A high-dose nebulizer treatment with albuterol can also help drive potassium into cells.

3. Remove Potassium from the Body

These treatments provide the definitive solution by actually eliminating the excess potassium.

• Diuretics: Loop diuretics, like furosemide, can be given to increase the excretion of potassium in the urine, but this is only effective if the patient has adequate kidney function.
• Potassium-Binding Resins: These are medications given orally or as an enema that bind to potassium in the intestines and remove it from the body in the stool.
• Dialysis (Hemodialysis): This is the fastest, most effective, and definitive way to remove potassium from the body. It is the primary treatment for patients with severe hyperkalemia who have kidney failure.

Once the patient is stabilized, long-term management will focus on treating the underlying cause, such as managing chronic kidney disease, adjusting high-risk medications, and sometimes, counseling on a low-potassium diet.

Clinically, I always tailor treatment to the cause whether it’s stopping a drug, managing kidney failure, or addressing acidosis or tissue damage.

Hyperkalemia is a serious and potentially fatal electrolyte disorder that occurs when the blood’s potassium level rises to a dangerous level. It is most often a complication of chronic kidney disease or a side effect of common medications used to treat high blood pressure and heart failure. Its danger lies in its silence; it often produces no symptoms until it reaches a level that can destabilize the heart’s electrical rhythm. The key to preventing this medical emergency is the careful management of underlying kidney disease and an awareness of the risks of certain medications. If you have been diagnosed with a high potassium level, it is a sign that your body’s delicate chemical balance is off. Working closely with your doctor to treat the underlying cause and lower your potassium level back to a safe range is essential for protecting your heart and your overall health.

National Kidney Foundation. (2023). Potassium and Your CKD Diet. Retrieved from https://www.kidney.org/atoz/content/potassium

The Merck Manual Professional Version. (2023). Hyperkalemia. Retrieved from https://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/electrolyte-disorders/hyperkalemia

American Heart Association. (n.d.). Potassium. Retrieved from https://www.heart.org/en/health-topics/high-blood-pressure/changes-you-can-make-to-manage-high-blood-pressure/how-potassium-can-help-control-high-blood-pressure