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Draft: not yet reviewed by a clinician

Use this page to prepare questions for your care team. It does not replace their advice. Your own targets and doses come from your nephrologist, diabetes team and renal dietitian.

Blood potassium

In short

Potassium keeps your heart beating in rhythm and your muscles working. The kidneys remove the extra, so as kidney function falls, blood potassium can rise. A very high level can cause a dangerous heart rhythm, often with no warning symptoms (MedlinePlus). Food is only one cause: medicines, high glucose or missed insulin, constipation and acid build-up often matter more (KDIGO 2024). A level that is too low is also risky. Know your last result, and know the two numbers that mean "call today" (6.0) and "go now" (6.5).

Your numbers

Potassium is the same number in mmol/L and mEq/L, so there is one table for both unit systems.

Result (mmol/L = mEq/L) What it means What to do
under 3.5 low Call your team soon. Do not cut potassium foods unless told to
about 3.5–5.1 the usual normal range (labs vary a little; your lab's range wins) Keep doing what you do. If you have a potassium limit, keep it until your team changes it; if you have none, you do not need one while it stays normal
5.2–5.5 above normal Your team looks for the cause, may repeat the test and review food and medicines
5.6–5.9 high Tell your team promptly. KDIGO lists steps for any potassium over 5.5 (below)
6.0–6.4 moderate hyperkalemia (KDIGO) Call your team today. If you feel unwell, get checked in hospital now; otherwise repeat the test within 24 hours
6.5 or more severe hyperkalemia (KDIGO) Emergency: call 911 or go to the emergency department now

Normal range from MedlinePlus; action levels from KDIGO 2024, Table 28 and Figure 32. KDIGO counts more than 5.0 as high when it describes how common high potassium is.

How often: with each kidney check, and 2–4 weeks after starting or increasing an ACE inhibitor or ARB (KDIGO 2024, practice point 3.6.2). Finerenone is not started if potassium is over 5.0 mEq/L, and potassium is checked 4 weeks after starting it (Kerendia label).

How high potassium feels

Often it feels like nothing. When there are symptoms, they can include weakness, nausea, palpitations (a fluttering or uneven heartbeat), a slow, weak or irregular pulse, chest pain, trouble breathing, or sudden collapse (MedlinePlus). That is why the lab number matters, not how you feel.

Causes besides food

Cause Why it raises potassium
Medicines: ACE inhibitors, ARBs, spironolactone, eplerenone, finerenone, beta-blockers, digoxin, heparin, amiloride, triamterene, NSAIDs (ibuprofen, naproxen), tacrolimus, cyclosporine, trimethoprim they reduce how much potassium the kidney can remove (KDIGO 2024, Table 26). SGLT2 inhibitors do not seem to raise it
Not enough insulin, or high glucose insulin moves potassium into cells; high glucose pulls water and potassium out of them (KDIGO 2024, Table 25; Sousa 2016)
Acid build-up (low bicarbonate) potassium shifts out of cells (KDIGO 2024, Table 25; Bicarbonate)
Constipation with advanced CKD the gut removes more of the potassium, so slow bowels keep more in (KDIGO 2024, Table 25)
The long gap between hemodialysis sessions the day after the 2-day gap has more heart-rhythm hospital stays (20.9 vs 11.0 per 100 patient-years) and more deaths (Foley 2011)
Food, especially potassium additives and salt substitutes additive potassium is absorbed best (Potassium in food)

False highs

Sometimes the blood in the tube is high but the blood in your body is not. This is called pseudohyperkalemia. Causes include a tight tourniquet, clenching or pumping your fist during the draw, red cells breaking open (a "hemolyzed" sample) after a hard draw, rough handling or a delay before the sample is processed, and very high platelet or white-cell counts. Serum results also run a little higher than plasma results (KDIGO 2024, Table 25). Potassium also varies by 0.24–0.73 mmol/L over a day. A surprise result is usually repeated, but do not assume a high result is false: call as the table says.

Low potassium

Below about 3.5 mmol/L is low. Causes include water pills (diuretics), vomiting or diarrhea, and low magnesium. Symptoms can be weakness, cramps, constipation and palpitations; a large drop can cause dangerous heart rhythms (MedlinePlus). People on peritoneal dialysis sometimes run low and need more potassium, not less (DaVita). Both low and high potassium are linked with a higher risk of death (KDIGO 2024, Figure 31).

What helps

KDIGO sets out the steps for potassium over 5.5 mmol/L in this order (KDIGO 2024, Figure 32):

  1. Fix what can be fixed. Review medicines such as NSAIDs and trimethoprim. Look at food with a renal dietitian, especially processed foods and salt substitutes (KDIGO 2024, practice points 3.11.5.1–3.11.5.2).
  2. Medicines that lower potassium, chosen by your team: a water pill, treatment for low bicarbonate, or a potassium binder.
  3. Last resort: lowering or stopping an ACE inhibitor, ARB or finerenone. Stopping them is linked with more heart problems, so the team tries to restart them later.

High potassium on an ACE inhibitor or ARB "can often be managed" by lowering potassium rather than stopping the medicine (KDIGO 2024, practice point 3.6.3).

What to do

  • Know your last potassium result and its date. Write it on your lab tracker.
  • Ask whether you need a potassium limit at all. Limit potassium only if your blood level is high and your team says so (Potassium in food).
  • At the blood draw, keep your hand relaxed and do not pump your fist.
  • Keep a list of the medicines you take that raise potassium. Show it to every prescriber.
  • Avoid NSAIDs such as ibuprofen and naproxen unless your kidney team says otherwise (Medicines to avoid).
  • Keep your bowels moving: fiber from low-potassium foods, fluid within your limit, and ask about a laxative if needed.
  • Keep glucose in range and never skip your basal (background) insulin. When you are ill, follow your sick-day plan.
  • On hemodialysis, never skip or shorten a session, and take extra care with potassium over the long gap (Dialysis days).
  • Never delay treating a low because of potassium. Treat it first (Treating a low).

In the app

Add a potassium result under Labs. At 6.0 mmol/L or more the app shows a red alert with the same advice as the table above, even if you never open "Suggest targets". A fresh result also changes the app's potassium review ceiling: normal relaxes it one step, high tightens it, and low removes it (design note 05). See Targets and warnings.

Examples

  • A new medicine. Three weeks after starting an ACE inhibitor, Rosa's potassium is 5.4. Her team looks at her food diary, finds a salt substitute and two glasses of orange juice a day, and swaps them. The ACE inhibitor stays, and the repeat is 4.9.
  • A hemolyzed sample. Tom's result is 6.1 and the report says "hemolyzed". He calls his team the same day. He feels well, so they repeat it within 24 hours: 4.8.
  • An emergency. On Monday morning, after the weekend gap, Jean feels weak and her pulse is slow and uneven. Her family calls 911. Her potassium is 7.0.
  • Running low. On peritoneal dialysis, Kai's potassium is 3.2. His team adds potassium-rich foods rather than limiting them.

Ask your care team

  1. What was my last potassium, and do I need a limit? What number?
  2. Which of my medicines raise potassium?
  3. Should I take a potassium binder? How does it fit around meals and other medicines?
  4. Could constipation, high glucose or low bicarbonate be part of the cause?
  5. What should I do if my result is high but I feel fine?
  6. Who do I call after hours about a lab result?

Get help now if…

Call 911 (or your local emergency number)

A lab or your team tells you your potassium is 6.5 mmol/L or more, or you have fainting, a very slow, weak or irregular pulse, chest pain or sudden severe weakness, especially if your potassium has been high (KDIGO 2024, Table 28; MedlinePlus). Do not drive yourself.

Call your care team today

A potassium of 6.0–6.4 mmol/L: if you feel unwell, get checked and treated in hospital; if you feel well, the test should be repeated within 24 hours (KDIGO 2024, Table 28). Also call for vomiting or diarrhea, and check your ketones. If you cannot keep liquids down for more than 4 hours, or you have ketones with vomiting, that is an emergency (CDC; Sick days). Full list: Get help now.

Sources

Not yet reviewed by a clinician. Facts and sources last checked 2026-10-06.