A High Potassium with Normal Kidney Function
The most common reason for a raised potassium on a routine sample is that potassium leaked out of blood cells after the draw, not that it was high in you. It even has a name: pseudohyperkalemia. With normal kidney function and no symptoms it is the first thing to exclude, by repeating the test with attention to how the blood is taken and handled. A genuinely raised potassium is a different matter, because it affects heart rhythm. A markedly high result is acted on straight away, not repeated at leisure.
The pattern on your report
- Potassium High · mild Key
- Creatinine Normal Key
- eGFR Normal Key
- Bicarbonate Normal Supporting
Printed as: Bicarbonate in mmol/Lor mEq/L— Same number. Reports may label it bicarbonate, HCO3 or total CO2.Creatinine in umol/Lor mg/dL— Far apart: 88 umol/L is about 1.0 mg/dL. A creatinine read against the wrong reference range is one of the more common ways to frighten yourself unnecessarily.eGFR in mL/min/1.73m2— One notation, though the equation behind it has changed over time and differs between countries.Potassium in mmol/Lor mEq/L— Identical figures for potassium, so 5.4 mmol/L is 5.4 mEq/L.
Why the numbers look like this
Almost all of the body's potassium sits inside cells, at a concentration far higher than in the plasma around them. Anything that lets cells leak on the way to the analyzer therefore raises the measured potassium without a single molecule moving in your body: a difficult draw, a fine needle, clenching your fist against the tourniquet, a sample that sat too long or got cold or shaken in transit.
Blood allowed to clot into serum leaks more than blood collected into plasma, which is why serum potassium reads a little higher as a matter of course, and considerably higher when the platelet or white cell count is up. Inside the body, the kidneys handle nearly all potassium excretion. That is why a truly raised potassium almost always comes with a reason the kidneys are not doing it, which is either reduced function or a drug that blocks the pathway.
Not being flagged is not the same as normal
Reference ranges typically top out somewhere between 5.0 and 5.3 mmol/L, and where a laboratory draws that line depends partly on whether it runs serum or plasma, since serum sits higher for the reason above. That makes 5.4 a very commonly flagged result and a rarely meaningful one. The number that changes what happens next sits considerably higher: from around 6.0 upward the risk to heart rhythm becomes the governing concern, and the result is dealt with that day, not repeated at the next convenient appointment.
What else on the report can hide this
The rest of the panel usually settles it. Creatinine and eGFR set how likely a genuine rise is: the less the kidneys are excreting, the less it takes. A low bicarbonate suggests a metabolic acidosis driving potassium out of cells, which frequently accompanies a real rise. A very high platelet or white cell count is also a recognized cause of a falsely high serum potassium, answered by collecting plasma instead of serum. But one line on the report outranks all of that: if the laboratory has commented that the sample was hemolyzed, the comment is the result, and the potassium figure printed beside it should not be interpreted at all.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Potassium released from cells after the draw
No symptoms, normal kidney function, and often a hemolysis comment on the report or a memorably difficult blood test. Repeating it properly resolves it, and nothing else needs doing first.
- Common
Medications
ACE inhibitors, ARBs, spironolactone and other potassium-sparing diuretics, NSAIDs, trimethoprim, heparin, non-selective beta-blockers, and the transplant drugs tacrolimus and ciclosporin. Between them they are the most common cause of a genuine rise in someone whose kidneys work, and the rise usually appears within weeks of starting or increasing one.
- Common
Potassium supplements and salt substitutes
Low-sodium table salt is usually potassium chloride, and it is easy to use a lot of it without registering that as taking potassium. It rarely comes up unless asked about directly.
- Common
Reduced kidney function that the creatinine does not show
Creatinine depends on muscle mass, so an older or frail person can have meaningfully reduced function with a creatinine that still prints inside its range. The eGFR handles this better, though not perfectly.
- Uncommon
A very high platelet or white cell count
Potassium released from those cells as the sample clots. A plasma sample reads normal, and the blood count on the same panel is the clue.
- Uncommon
Type 4 renal tubular acidosis
Common in longstanding diabetes. A mild persistent hyperkalemia with a mildly low bicarbonate and kidney function that can look close to normal.
- Uncommon
Uncontrolled diabetes or insulin deficiency
Insulin moves potassium into cells, so a high glucose with too little insulin lets it sit in the blood. A raised glucose on the same panel is the clue, and it corrects as the glucose does.
- Uncommon
Adrenal insufficiency
A raised potassium alongside a low sodium, low blood pressure, fatigue, salt craving or darkened skin. The sodium is what makes the pair worth noticing.
- Rare
Rhabdomyolysis or tumor lysis
Not a routine-panel finding. There is a crush injury, extreme exertion, dark urine, or recent chemotherapy, and the person is unwell. CK or urate is markedly raised.
- Rare
Familial pseudohyperkalemia
Lifelong, harmless, and worse when the sample is cooled before analysis. Recognized by a long history of raised readings with nothing ever coming of them.
What is usually checked next
- Repeat with a careful draw, ideally as plasma rather than serum Separates a leak in the tube from a rise in you. It is the first test every time, unless the level is high enough that waiting is not safe.
- ECG Shows whether the heart rhythm is being affected, which is the only time-critical part of this. Done immediately when the potassium is markedly raised, rather than after a repeat.
- Kidney function with bicarbonate Checks the two things that make a genuine rise possible: excretion and acid-base state.
- A review of medicines, supplements and salt substitutes Finds the most common real cause. Salt substitutes in particular need asking about by name.
- Morning cortisol Tests for adrenal insufficiency. Indicated when the potassium is up and the sodium is down.
When to seek care sooner
- Emergency A potassium the laboratory reports as critically high
- Emergency Palpitations, a very slow pulse, fainting, or chest pain with a raised potassium
- Emergency New muscle weakness or paralysis, particularly in the legs
- Same day A raised potassium with new or worsening kidney function
- Same day A raised potassium with a low sodium and low blood pressure
- Soon A rise that persists on repeat testing while on an ACE inhibitor, ARB or spironolactone
Questions worth bringing to your appointment
- Was the sample reported as hemolyzed, and should this be repeated before we act on it?
- Could any of my medicines be responsible, and is there an alternative?
- Do I use a low-sodium salt substitute, and does that matter here?
- Does this level need an ECG, or is repeating the blood test enough?
- If it stays up, what would be the next step?