Potassium
Potassium is a mineral that helps your nerves, muscles and heart work. This test shows how much is in your blood.
AI-verified against cited sources. Awaiting expert reviewAlso called K, K+LOINC 2823-3
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What it is
Potassium is an electrolyte, a mineral with a small electric charge. Most of it sits inside your cells, and only a small amount circulates in the blood, so small changes in the blood level can matter. It helps your muscles contract, your nerves send signals and your heart keep a steady rhythm. Your kidneys remove extra potassium in urine, and insulin and hormones such as aldosterone help move it in and out of cells.
Why it matters
Both low and high potassium can change how the heart beats. For that reason it is part of most routine blood panels, and it is checked in people with kidney disease or who take medicines that affect potassium. Mild changes usually cause no symptoms. A high result can also be a false alarm from the way the blood was drawn or handled, so a repeat test is common.
If it’s low
A lower potassium level most often comes from losing potassium through the gut or kidneys, or from water pills (diuretics). Mild lows often cause no symptoms. A lower level can cause muscle weakness, cramps, tiredness, constipation or an irregular heartbeat. Your clinician can put your result in context.
Common causes
- Water pills (diuretics), the most common medicine cause
- Vomiting, diarrhea or heavy sweating
- Overuse of laxatives
- Low magnesium, which makes the kidneys lose more potassium
- Medicines or conditions that move potassium into cells, such as insulin and some asthma medicines (beta-2 agonists)
- Eating a lot of real licorice, which can make the body lose potassium
- Hormone conditions that make the body lose potassium, such as primary aldosteronism or Cushing syndrome
- Heavy alcohol use
- Too little potassium in the diet (rarely the only cause)
What can help
- Ask your clinician whether a medicine, diarrhea, vomiting or heavy sweating could explain it
- Ask whether your magnesium should be checked too
- Eat potassium-rich foods such as beans, lentils, potatoes, tomatoes, bananas, citrus fruit, yogurt and nuts, unless a clinician has told you to limit potassium
- Talk with your clinician before taking potassium supplements or using salt substitutes
If it’s high
A higher potassium level can come from the blood sample itself, from kidneys that clear potassium more slowly, or from certain medicines. A true high level can affect the heart's rhythm, which is why labs pay close attention to it. Because sample problems are common, clinicians often repeat a surprising result before acting on it. Your clinician can put your result in context.
Common causes
- A sample problem, such as damaged red cells in the tube (hemolysis), a long or tight tourniquet, fist clenching, or a delay before the blood was spun (called pseudohyperkalemia)
- Reduced kidney function, which slows removal of potassium
- Medicines that raise potassium, including ACE inhibitors, ARBs, potassium-sparing diuretics, NSAID pain relievers and trimethoprim
- Potassium supplements, or large amounts of potassium from food or potassium-based salt substitutes
- Poorly controlled diabetes or acid build-up in the blood
- Addison disease, an adrenal gland condition
- Injury, burns or surgery, when cells release potassium
- Very high platelet or white blood cell counts, which can release potassium in the tube
What can help
- Ask whether the test should be repeated with a fresh, carefully drawn sample
- Tell your clinician about every medicine, supplement and salt substitute you use
- Ask whether your kidney function should be checked
- Ask your clinician or a dietitian before changing the potassium in your diet
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 3.5–5.2 mmol/L. Source: Labcorp, Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center). Labs treat below 3 mmol/L or above 6.1 mmol/L as urgent.
- 1+ (this one applies)3.5–5.2 mmol/L
Sources: Labcorp, Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)
See Potassium by age and sex, with the U.S. survey numbers where they exist.
UK Kidney Association hyperkalaemia severity (2026 update)
- Mild5.5 to under 6 mmol/L
- Moderate6 to under 6.5 mmol/L
- Severe6.5 and above mmol/L
If this applies to you
Potassium means a little more for some people. Open the one that fits you.
Kidney disease or at risk
High potassium is uncommon when eGFR is above 60 and becomes more common as kidney function falls, though it is not inevitable. Some common blood pressure and kidney medicines can raise it too. KDIGO 2024 lists potassium among the CKD lab changes to follow.
Age 65 or older
The American Geriatrics Society notes that some medicine combinations raise the chance of high potassium when kidney function is reduced. Examples are two blood pressure medicines that act on the renin-angiotensin system (such as ACE inhibitors or ARBs), one of these with a potassium-sparing diuretic, or the antibiotic trimethoprim-sulfamethoxazole with an ACE inhibitor, ARB or ARNI.
Prediabetes or diabetes
Some blood pressure and kidney-protecting medicines can push potassium up, and diuretics can push it down. The ADA suggests checking potassium and eGFR when these medicines are started and periodically after that.
On gender-affirming hormones
Spironolactone, a common testosterone blocker, can raise potassium, though WPATH calls this uncommon and usually short-lived. The Endocrine Society suggests checking it every 3 months in the first year, then once a year.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Potassium by age and sex: every percentile as a table, with a download.
What can affect your result
- Sample handling: hemolysis, fist clenching, a long tourniquet time, delays before the blood is spun, or chilling a clotting sample can all raise the result
- Serum or plasma: serum usually reads a little higher than plasma, by up to about 0.4 mmol/L, because platelets release potassium as blood clots
- Very high platelet counts (above about 500 ×10³/µL) or white blood cell counts
- Acid-base balance: as the blood becomes more alkaline, potassium moves into cells and the blood level falls
- Medicines, kidney function, diet and fluid losses
- Age: babies have higher ranges than adults
- Lab differences: Labcorp lists 3.5–5.2 mmol/L and Mayo Clinic Laboratories lists 3.6–5.2 mmol/L
- Hemolysis (damaged red cells in the tube) falsely raises potassium. Fist clenching, a long or tight tourniquet and a difficult draw can do the same.
- Delays before the blood is spun, or chilling a clotting sample, let potassium leak out of cells and falsely raise the result. Labcorp asks for serum or plasma to be separated within 45 minutes.
- Serum reads slightly higher than plasma, by up to about 0.4 mmol/L, because platelets release potassium as blood clots. Very high platelet counts (above about 500 ×10³/µL) can raise serum potassium much more. Very high white blood cell counts can also raise it, and plasma samples are more affected by that.
- A tube with EDTA additive carried over into the sample (wrong order of draw) falsely raises potassium. Drawing above an IV line that holds potassium fluids can contaminate the sample.
- Many medicines raise or lower potassium. Tell your clinician about everything you take.
Hours to days. Potassium can shift within hours with insulin, vomiting or diarrhea, and changes in acid-base balance. It follows medicine changes over days.
When to talk to a clinician
Contact the clinician who ordered the test soon if your potassium is outside your lab's range. Many labs treat a result below 3.0 or above 6.1 mmol/L as urgent. UK Kidney Association guidance suggests repeating a mildly high result (5.5–5.9 mmol/L) within about 3 days and a moderately high one (6.0–6.4) within a day, and urgent hospital assessment for 6.5 or higher. Call 911 or your local emergency number for chest pain, a racing, pounding or very slow heartbeat, fainting, severe muscle weakness or trouble breathing.
Questions you could ask
- Which of my medicines or health conditions affect potassium, and how often should it be checked?
- Could the way the blood was drawn or handled explain this result, and should we repeat the test?
- Could any of my medicines, supplements or salt substitutes raise potassium?
- Should we check my kidney function?
- Could a medicine, vomiting, diarrhea or sweating explain a lower result?
- Should we check my magnesium and kidney function too?
Questions people ask
Why was I asked to repeat my potassium test?
A high potassium result is often a sample problem, such as damaged red cells in the tube. A repeat on a fresh, carefully drawn sample shows whether the high level is real. A repeat is also common after a result that is low or that doesn't fit how you feel.
Why is serum potassium different from plasma potassium?
When blood clots to make serum, platelets release a little potassium. Serum therefore usually reads slightly higher than plasma, by up to about 0.4 mmol/L. Your report may say which one was measured.
Will eating potassium-rich foods like bananas change my result?
If your kidneys work well, food alone usually doesn't push your level out of the range, because the kidneys remove extra potassium. Diet matters more for people with kidney disease or who take medicines that raise potassium, so ask your clinician or a dietitian what is right for you.
Why do labs list slightly different ranges?
Each lab sets its range using its own method and patients. Labcorp lists 3.5–5.2 mmol/L and Mayo Clinic Laboratories lists 3.6–5.2 mmol/L for people over 1 year old. Use the range printed on your own report first.
Is mEq/L the same as mmol/L for potassium?
Yes. Potassium carries a single charge, so the numbers are the same in both units. A result of 4.2 mmol/L is 4.2 mEq/L.
Show the science and sources
Units
- 1 mmol/L = 1 mmol/L
- 1 mmol/L = 1 mEq/L
Is a change real?
Potassium naturally varies about 4.1% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 13% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Critical appraisal and meta-analysis of biological variation estimates for kidney related analytes (Jonker N et al., EFLM WG-BV).
For clinicians and researchers
Most body potassium is intracellular, so the serum level depends on both total stores and shifts across cell membranes (insulin, beta-2 agonists, acid-base state). Labcorp notes that a pH rise of 0.1 lowers potassium by about 0.6 mmol/L, so the serum level must be read alongside acid-base status. Pseudohyperkalemia is common: hemolysis, fist clenching, prolonged tourniquet time, EDTA carryover, delayed separation, excessive centrifugation and chilling clotted samples all raise the measured value. Serum values exceed plasma by up to about 0.4 mmol/L because platelets release potassium during clotting, and the gap widens in thrombocytosis (Labcorp cites a platelet count above 500 ×10³/µL) and with erythrocytosis. Marked leukocytosis, as in chronic lymphocytic leukemia (CLL), can raise potassium through fragile-cell lysis, and heparinized plasma can then read higher than serum (reverse pseudohyperkalemia). A lithium-heparin plasma or blood-gas (whole blood) potassium is commonly used to check for pseudohyperkalemia. Definitions vary: the UK Kidney Association guideline adopts the European Resuscitation Council threshold of 5.5 mmol/L and grades hyperkalemia as mild (5.5–5.9), moderate (6.0–6.4) and severe (6.5 or higher), and the Merck Manual defines hypokalemia as below 3.5 mmol/L, with mild (3.0–3.4), moderate (2.5–3.0) and severe (below 2.5) grades. Hypomagnesemia often accompanies hypokalemia, and both deficits need correcting to stop ongoing renal potassium wasting. Reference intervals: Labcorp 3.5–5.2 mmol/L (over 1 year), Mayo Clinic Laboratories 3.6–5.2 mmol/L (1 year and older). ARUP calls below 3.0 or above 6.1 mmol/L, and Michigan Medicine Laboratories below 2.5 or above 6 mmol/L.
LOINC 2823-3 (primary), 77142-8, 6298-4. Specimen: serum-or-plasma.
Sources
- Potassium (test 001180), Labcorp
- Potassium, Serum (test ID KS), Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)
- Critical Values List (CORP-APPEND-0104A, Rev. 46), ARUP Laboratories (2026)
- Critical Value Policy, Michigan Medicine Laboratories (MLabs) (2025)
- Clinical Practice Guidelines: Treatment of Acute Hyperkalaemia in Adults (updated July 2026), UK Kidney Association (2026)
- Pseudohyperkalemia in Serum: A New Insight into an Old Phenomenon, Clinical Medicine & Research (2008)
- Pseudohyperkalemia in Serum and Plasma: The Phenomena and Its Clinical Implications, Indian Journal of Clinical Biochemistry
- Hypokalemia, Merck Manual Professional Version
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.