When too much potassium becomes dangerous

You've probably heard that potassium—a mineral found in bananas, potatoes, milk, tomatoes, fish, and many other foods—plays a starring role in your good health. But for about one in 25 people, potassium in the blood can become too high or too low, raising the risk for heart and muscle problems.

Minor imbalances can usually be treated with supplements and medications. But more severe imbalances can cause muscle weakness, irregular heart rhythms, nausea, numbness, diarrhea, constipation, cramping, and other warning signs. But often, a too-high or too-low potassium level has few, if any, symptoms.

For older adults, it's critical to have your blood tested routinely, especially if you have another condition that puts you at risk for elevated potassium in the blood. Here's what you should know about the test itself.

Serum K: What's in a name? Serum K refers to the amount of potassium in your blood. The letter K is the scientific symbol for potassium; the word "serum" means the fluid part of blood.

Why does serum K matter for heart health? Potassium helps with the conduction of electrical signals in the thick, muscular layer of heart tissue called the myocardium. Having too much or too little K can lead to irregular heartbeats. Even small increases or decreases can affect your heart, as well as other muscles.

Why might my doctor order a serum K test? Your doctor may check your serum K as part of routine blood work, to help diagnose or keep tabs on kidney disease—the main cause of high potassium levels. If you take medications for high blood pressure or heart failure (such as diuretics, beta-blockers or ACE inhibitors), be sure and tell your doctor, as they can affect potassium levels. Be sure to also mention if you have irregular heart rhythms, uncontrolled diabetes, or signs of muscle weakness.

A potassium check may also be part of your routine care if you have high blood pressure or receive kidney dialysis. People with diabetes and congestive heart failure are also at higher risk for high potassium levels. Taking some diuretics and antibiotics, overdoing laxatives, having an eating disorder, and having low magnesium may raise the risk for low potassium.

What if my serum K is high? A high potassium level is referred to as hyperkalemia. For mild hyperkalemia, your doctor may recommend avoiding foods high in potassium. These include bananas, cantaloupe, dried fruit, fruit juices, oranges, mangos, avocados, tomatoes, potatoes (white and sweet), Brussels sprouts, milk, yogurt, lentils, seeds, and nuts.

Other high-potassium foods include clams, sardines, scallops, lobster, whitefish, salmon (and most other fish), pinto beans, kidney beans, black beans, navy beans, whole-grain bread, wheat bran, chocolate, and coffee. Replace these foods with low-potassium foods like apples, berries, broccoli, carrots, peppers, kale, squash, eggplant, and pasta. Your doctor may recommend avoiding salt substitutes that contain potassium.

If you take medications for your heart or blood pressure, your doctor may also make a change in those medications, as well as recommend medications to lower potassium levels or other treatments.

What if my serum K is low? Low potassium is called hypokalemia. If levels are just slightly low, your doctor will likely suggest eating more potassium-rich foods. You may also be prescribed potassium supplements. For severely low levels, you may receive potassium through an IV.