Hyperkalemia (High Potassium): Causes and What to Do

Your lab report shows a potassium above the top of the printed range, and you want to know how worried to be. Here is what almost nobody puts first: on a routine outpatient panel, the most common cause of a high potassium is not a disease — it is the tube. Potassium is packed inside your cells, so a few red cells breaking during the draw are enough to push the number up while the potassium circulating in you is normal. This page covers how to spot that, the real causes once the value is confirmed, when to call a doctor the same day, and what happens next.

First: is this actually abnormal?

There is no universally agreed cutoff for hyperkalemia. The most widely used threshold is 5.5 mEq/L, and the international KDIGO conference states that this cutoff "varies depending on the individual laboratories and differs between plasma and serum measurements" — serum runs higher than plasma.¹ The National Kidney Foundation puts the usual normal band at 3.5 to 5.0, adding "depending on the laboratory that is used."² The only boundary that means anything is the one printed on your own report.

A value just over the line is therefore not "a disease." For scale: potassium at or above 5.0 mEq/L is found in roughly 1.5% of the general population, and in about 5.6% of people who recently started an ACE inhibitor or ARB.¹ In a Swiss university emergency department, only 0.3% of patients reached 6.0 mEq/L or more.¹ The worrying zone is narrow, and you are probably not in it.

For what this marker is, its full range, and the opposite problem (low potassium), read the parent guide: potassium blood test. It is measured within the electrolyte panel and the comprehensive metabolic panel, beside sodium, chloride and bicarbonate, and never read apart from your kidney function and medication list.

A note on units. US reports print potassium as mEq/L or mmol/L. The two are numerically identical for potassium — 5.4 mEq/L is 5.4 mmol/L — so there is nothing to convert. This page uses mEq/L, as FDA labeling and the cardiology guidelines do.³⁴

The leading cause of a high potassium: the draw itself

This is pseudohyperkalemia — the potassium measured in the tube is high while the potassium in your bloodstream is not.⁵ Not a laboratory curiosity but a mass phenomenon. Hemolyzed samples, in which red cells have ruptured, run as high as 3.3% of all routine specimens and account for 40% to 70% of every unusable sample — nearly five times more than all other causes of a rejected tube combined.⁶ Potassium is the analyte most exposed, because it is concentrated inside those cells and spills into the sample the moment they break.⁵

Every trigger is preanalytical — collection and handling, not your body:⁵¹

• Hemolysis, from a difficult stick, a fragile vein, or too much suction — by far the most common;
• Clenching or pumping your fist while the needle is in: the exercising forearm muscle leaks potassium while the tourniquet prevents it washing away;⁵
• A delay before the sample is spun, a tube sent through a pneumatic chute, or a specimen left to get cold — all let potassium seep out of cells;
• A very high platelet or white cell count. In a two-laboratory US study, about 14% of serum samples with platelets above 500 × 10⁹/L read more than 1 mEq/L higher than the same patient's whole-blood potassium, and over 25% did when white cells exceeded 50 × 10⁹/L — highest in chronic lymphocytic leukemia.⁷ A markedly high platelet count or white blood cell count on the same CBC can explain the number by itself.

⚠️ The tourniquet claim you have probably read is wrong as usually stated. Under standardized pressure, one minute of venous stasis makes potassium go down 2.8%, three minutes 4.8%.⁸ What a tight or fumbled draw really costs you is hemolysis, not stasis. Blame the difficult stick, not the strap.

In practice: a competent lab flags a hemolyzed specimen. If you feel well and the draw was long or awkward, ask whether the sample was hemolyzed and should be redrawn — that one question resolves a large share of these results. See also how a blood draw works and blood tube colors.

The real causes, most common first

Once the value holds up on a clean draw, this is the order a clinician thinks in.

1. Kidney disease. The kidney excretes potassium, and one that works less excretes less: declining kidney function is the single largest risk factor for hyperkalemia.¹ Hence creatinine and eGFR beside your potassium, plus BUN, sometimes cystatin C and urine albumin — the kidney function panel.

2. Medications — very often the answer. Check your prescription list first:¹³

• ACE inhibitors (lisinopril, enalapril) and ARBs (losartan, valsartan);
• Mineralocorticoid receptor antagonists and potassium-sparing diuretics: spironolactone, eplerenone, finerenone, amiloride;
• NSAIDs — ibuprofen, naproxen — including over the counter;
• Beta blockers, heparin, digoxin, potassium supplements;
• Trimethoprim, alone or as trimethoprim-sulfamethoxazole (Bactrim, Septra). FDA labeling warns that even recommended doses can raise potassium in people with kidney impairment or on other potassium-raising drugs.⁹ The effect is startling: among older adults already on spironolactone, a trimethoprim-sulfamethoxazole prescription carried an adjusted odds ratio of 12.4 (95% CI 7.1–21.6) for hospitalization with hyperkalemia within 14 days, versus amoxicillin.¹⁰

A high potassium on an ACE inhibitor, ARB or spironolactone does not mean the drug should be stopped: these protect your heart and kidneys, and the heart failure guidelines build potassium monitoring into their use precisely so they can be continued.⁴ That call belongs to your clinician.

3. Diabetes and heart failure. These, with coronary disease, are the comorbidities that most raise the risk.¹ In diabetes the mechanism runs through low aldosterone and through insulin, which normally drives potassium into cells — hence glucose and A1c in the workup.

4. Massive cell breakdown. Rhabdomyolysis, burns and major trauma dump potassium out of cells at once.¹ A hospital situation, with a very high CK.

5. Adrenal insufficiency — much rarer than its reputation. An aldosterone deficit does raise potassium. But in a hospital series of 112 hypoaldosteronism episodes, only 5% (6 of 112) were primary adrenal insufficiency; almost all were acquired and isolated, in older adults (median age 77), mean potassium 5.4 mEq/L.¹¹ Aldosterone, renin and cortisol are ordered only when the picture points there.

What should send you to a doctor right away

The number to remember is 6.0 mEq/L. Above it, KDIGO recommends cardiac monitoring and a 12-lead ECG, and 6.0 mEq/L or more warrants immediate medical contact, the same day.¹ Above 6.5 mEq/L the guidance goes further — intravenous calcium to protect the heart, even before an ECG is available — and care is inpatient and urgent.¹ The National Kidney Foundation draws the same line, calling above 6.0 the danger zone.²

If your result is 5.2, 5.4 or 5.6 mEq/L, this is not you. You are in the common situation of a modest elevation that gets rechecked before anyone concludes anything.

Whatever the number, get seen promptly if you have:

• muscle weakness starting in the legs and moving upward;
• numbness or tingling in the limbs;
• palpitations, a very slow pulse, chest pain, shortness of breath, or faintness.²

These are uncommon, and many people with hyperkalemia have no symptoms at all.¹ Feeling fine proves nothing — the confirmed number is what decides.

What your doctor will do next

A repeat draw, done properly. The explicit first step in any new hyperkalemia: confirm before you treat.¹ In practice: no fist clenching, tourniquet off as soon as blood flows, tube to the lab fast, no chilling.

An ECG — but not to make the diagnosis. A 2025 study of 1,608 emergency department patients measured how well cardiologists reading ECGs detected hyperkalemia: sensitivity 0.39 to 0.47, specificity 0.76 to 0.81 — the ECG "is not an accurate tool for ruling-in or ruling-out hyperkalemia."¹² KDIGO says it plainly: up to half of hyperkalemic patients have a normal ECG, including some with extreme values.¹ The ECG measures the effect on your heart; it does not exclude the problem.

A metabolic panel with kidney markers, to situate kidney function and acid-base balance (bicarbonate).

A medication review, prescription in hand — including what you take without one: NSAIDs, supplements, salt substitutes. Glucose, CK or hormone tests may be added. For chronic hyperkalemia on heart- and kidney-protective therapy, potassium binders exist so those drugs can continue; see the potassium blood test guide.

What this result does NOT mean

It is not your diet. The most widespread misconception. In a person whose kidneys work, high potassium intake is not enough to cause hyperkalemia — the healthy kidney excretes far more than the diet supplies.¹ Giving up bananas will not fix an elevated number; potassium restriction only makes sense on medical advice, in moderate-to-severe kidney disease.¹² The real US dietary culprit is different: potassium-based salt substitutes ("no salt," "lite salt" — potassium chloride on the label) and supplements can genuinely raise your level if your kidneys are impaired or you take a potassium-raising drug. NIDDK tells people with kidney disease to season with herbs and spices instead, and to watch for potassium chloride in ingredient lists;¹³ FDA labeling for spironolactone names salt substitutes as a specific risk.³

It is not a sign of cancer. Potassium is not a tumor marker. Hyperkalemia can occur during the treatment of some cancers (tumor lysis) — unrelated to a routine panel result.

It is not proof of kidney failure. The kidney is the first thing to look at, not the conclusion; creatinine and eGFR settle that.

It is not a number to fix on your own. Stopping an ACE inhibitor, ARB or spironolactone yourself trades a lab value for cardiovascular risk. Both the NKF and the heart failure guidelines are explicit: do not stop these medicines unless a clinician tells you to.²⁴

Should you repeat the test, and when?

Yes, for the large majority of modest elevations — confirming a newly found hyperkalemia is the recommended first move.¹ The timing depends on the number and your situation; your clinician sets it. Three anchors:

• 6.0 mEq/L or above: not a "recheck in two weeks" situation. Immediate medical contact.¹
• A modest, symptom-free rise on a suspect specimen (hard stick, flagged hemolysis, high platelet or white cell count): a prompt redraw under good conditions, before any treatment.⁷
• A recently started or increased drug. FDA labeling for spironolactone is specific: check serum potassium within 1 week of starting or titrating, and regularly after — more often on other potassium-raising drugs or with impaired kidney function.³ The AHA/ACC/HFSA heart failure guideline sets the same expectation, recommending these drugs when potassium is below 5.0 mEq/L and eGFR above 30, with close monitoring thereafter.⁴

One more thing: under federal law, US laboratories must immediately alert the ordering clinician when a result falls in the critical or "panic" range.¹⁴ If nobody called you, that is already information.

Get your potassium interpreted by AI DiagMe

A high potassium is never read alone: it depends on your kidney function, your prescription list, your platelet and white cell counts, and how the blood was drawn. That cross-referencing separates a false alarm from a real problem.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

Bottom line

On a routine outpatient panel, a high potassium is first a question about the specimen: hemolysis accounts for 40% to 70% of unusable samples,⁶ and potassium is the first analyte to suffer for it.⁵ Compare yourself to the range on your report, treat 6.0 mEq/L as the line for same-day medical contact, and know that below it the standard move is a recheck, not treatment. Once confirmed, look in order: the kidneys, the prescription list — very often the answer — diabetes, and only rarely the adrenal gland. No value is read alone; what matters is your full profile, which is what AI DiagMe provides, alongside your physician.

Sources

Official US sources and peer-reviewed publications (PubMed) used for this guide: