High potassium with kidney disease: what to eat, what to stop, and when it’s urgent

If a blood test came back with a high potassium level and you also have kidney disease, you are in the most common situation a nephrologist sees. Potassium is one of the minerals the kidneys are responsible for clearing, so as kidney function falls, potassium tends to rise. Most of the time it is manageable with a few changes to food and medication. Occasionally it is an emergency. This guide explains how to tell the difference and what to do in each case.

What “high potassium” means

Potassium (chemists write it as K) is a mineral your muscles and nerves need to work, including the heart muscle. Your kidneys keep the level in the blood inside a narrow range by removing what you don’t need in urine.

A normal blood potassium level is roughly 3.5 to 5.0 mmol/L. Doctors call a level above 5.0 to 5.5 hyperkalemia, which simply means “high potassium in the blood.” How concerning it is depends on the number, how fast it rose, and whether it is affecting the heart:

• Mildly high (about 5.1 to 5.5): common with chronic kidney disease. Usually managed with diet and a medication review, then a repeat test.
• Moderately high (about 5.6 to 6.0): needs attention within days, not weeks. Your doctor will look for a cause and may change a medication.
• Severely high (above 6.0, or any level with symptoms): treat as urgent. See “When it’s an emergency” below.

One thing to know: a single high reading is sometimes a false alarm. If the blood sample sat too long, was drawn with a tight tourniquet, or the person clenched their fist repeatedly, red blood cells can leak potassium into the sample. If your number is unexpectedly high and you feel fine, your doctor may simply repeat the test before doing anything else.

Why kidney disease raises potassium

Healthy kidneys remove excess potassium every day. In chronic kidney disease, the kidneys filter less, so potassium that would normally leave in urine stays in the blood. The lower your eGFR, the less margin you have, which is why someone at stage 4 can get into trouble with a meal that someone at stage 2 would never notice.

Kidney disease rarely acts alone, though. Most high potassium readings have two or three causes stacked together:

• Blood pressure and heart medicines that are good for the kidneys but hold on to potassium: ACE inhibitors (lisinopril, enalapril), ARBs (losartan, valsartan), spironolactone and eplerenone, and finerenone (Kerendia), a newer kidney-protective drug. These are usually worth keeping; the fix is adjusting the dose or adding something else, not stopping them on your own.
• Potassium supplements and salt substitutes. “Lite” salt and most no-sodium salt substitutes are potassium chloride. For someone with kidney disease, they can raise potassium faster than any food.
• NSAID pain relievers such as ibuprofen and naproxen reduce blood flow to the kidneys and raise potassium. This matters for anyone being treated for foot, ankle or joint pain.
• Uncontrolled diabetes. High blood sugar pushes potassium out of cells into the blood.
• Dehydration and acute illness: a stomach bug, a missed dialysis session, a hot day without enough fluid.
• Certain antibiotics and other drugs, including trimethoprim (in Bactrim) and heparin.

Bring a complete list of everything you take (prescriptions, over-the-counter pain relievers, supplements, salt substitutes) to your appointment. The cause is often in that list.

Symptoms: usually none, which is the problem

Mild and moderate hyperkalemia usually causes no symptoms at all. People find out from a routine lab. That is why nephrologists check potassium so often in kidney disease.

When symptoms do appear, they tend to be vague: tiredness, muscle weakness or heaviness (often starting in the legs), nausea, tingling or numbness. These overlap with a dozen other things, so they are not reliable on their own. But if you have kidney disease and notice new muscle weakness, get a potassium check.

When it’s an emergency

Very high potassium can disturb the heart’s rhythm, and that can happen quickly. Go to an emergency room or call 911 (do not wait for a clinic appointment) if you have kidney disease and any of the following:

• A potassium result above 6.0, or a result your lab or doctor flagged as critical
• Heart palpitations, a fluttering or irregular heartbeat, or chest discomfort
• Sudden muscle weakness, especially if it is spreading or making it hard to walk
• Shortness of breath, light-headedness or fainting
• You take an ACE inhibitor, ARB or spironolactone and you’ve had vomiting, diarrhea or very little to drink for more than a day

In the ER, treatment is fast and well established: medicines that move potassium back into cells and protect the heart, then medicines or dialysis to remove it. People do well when they come in early.

What to eat, and what to go easy on

Food is the part people can act on today, and it is also where most of the bad advice lives. A few principles first:

• The goal is lower, not zero. Potassium is essential. Cutting it out entirely causes its own problems. Your nephrologist or a renal dietitian will give you a target that fits your stage and your labs.
• Portion matters as much as the food. A small serving of a high-potassium food is often fine; a large one is not.
• Plant foods are less of a problem than the lists suggest. Potassium from fruits, vegetables and beans is absorbed less completely than potassium from processed foods and supplements, and recent kidney guidelines have relaxed the old blanket restrictions. Processed foods with added potassium (check labels for “potassium chloride” or “potassium phosphate”) are a bigger concern than a tomato.

Foods that raise potassium quickly (limit or portion carefully): bananas, oranges and orange juice, cantaloupe, dried fruit (raisins, dates, apricots), avocado, potatoes and sweet potatoes, tomatoes and tomato sauce, cooked spinach, beans and lentils in large amounts, dairy in large amounts, nuts and seeds, chocolate, and salt substitutes.

Lower-potassium choices that fill the same spot on the plate: apples, berries, grapes, pineapple, peaches; cauliflower, cabbage, green beans, cucumber, peppers, onions, zucchini; white rice, pasta, bread; chicken, fish and eggs in normal portions.

Two kitchen techniques that help:

• Leaching potatoes and some root vegetables (peel, cut small, soak in a large pot of warm water for at least two hours, or boil, drain and boil again in fresh water) removes a meaningful share of the potassium.
• Draining and rinsing canned fruit and vegetables also helps, since some potassium moves into the liquid.

Ask for a referral to a renal dietitian if your potassium stays high despite changes, if you have diabetes to balance at the same time, or if the food lists feel unmanageable. One visit usually turns a confusing list into three or four concrete swaps. If swelling is part of the picture too, our guide to foods and drinks that reduce swelling covers the other half of the plate.

What your nephrologist may do

Depending on your number, your stage and what’s causing it, the plan may include:

• Repeat labs, sometimes within days, to confirm the trend
• Adjusting medications: changing a dose, switching a diuretic, or pausing something temporarily. Do not stop a blood pressure or kidney medicine on your own; some of them are protecting your kidneys more than they are raising your potassium.
• A potassium binder, a daily medicine that holds potassium in the gut so it leaves in the stool instead of entering the blood. Binders often let people stay on kidney-protective medicines they would otherwise have to stop.
• Treating the underlying driver: better blood sugar control, correcting acid levels in the blood, managing fluid.
• Dialysis adjustments for people already on dialysis.

When to see a nephrologist

If your potassium has been high more than once, or your kidney function is declining, a nephrologist can look at the whole picture (kidneys, blood pressure, diabetes and medications together) and keep you on the treatments that protect your kidneys without letting potassium get away from you.

Evolve Health’s nephrology and kidney care is offered at our offices in the Orlando area. Bring recent lab results and a full list of medicines and supplements to your first visit, or find a kidney specialist and book online. Swollen ankles often go with kidney trouble; our guide to swollen feet and ankles explains when that is a sign to act on.