Potassium is the main positively charged ion inside cells, and a blood test measures the fraction of it that circulates in serum or plasma. It is ordered as part of an electrolyte panel and is read with sodium, chloride, kidney function, and the heart's electrical activity in mind. The range printed on your report decides how the value is read.
Because the blood holds only a small part of the body's potassium, a result is a narrow window on a much larger store. That is why the sample itself, and the way it was handled, can matter as much as the physiology.
What the test measures
Potassium is the main positively charged ion inside cells, where most of the body's supply sits. Only a small share circulates in the fluid outside cells, and that is the share a blood test measures. The concentration outside cells matters because the difference in potassium across a cell membrane sets the electrical charge that nerve and muscle cells use.
The result is a concentration, not a count of the body's total potassium. A person can have a low total body potassium and a blood value inside the report's range, because the body moves potassium between cells and the blood to protect the concentration outside cells. The test also says nothing about how much potassium was eaten; it describes what is circulating at the moment of the draw.
Why it may be ordered
- As part of an electrolyte panel or a basic metabolic panel, with sodium, chloride, bicarbonate, urea, and creatinine.
- When kidney function is being reviewed, because the kidneys decide how much potassium is passed in urine.
- When a medicine that changes potassium handling is being taken, because the result is read with the medicine list.
- When a clinician is assessing muscle weakness, cramping, or an irregular heartbeat, alongside the rest of the assessment.
- When a condition that affects the adrenal glands or acid-base balance is being assessed.
- Before or after a procedure, where a clinician wants a current electrolyte value.
The unit on your report
| What you may see | Unit | What it reflects |
|---|---|---|
| Potassium, K, K+ | mmol/L | The potassium concentration in serum or plasma, in millimoles per litre. |
| Potassium | mEq/L | The same concentration in milliequivalents per litre. For potassium the two labels give the same number, because each ion carries a single charge. |
| Serum potassium, plasma potassium | mmol/L | The sample type. Serum and plasma can differ slightly, because clotting releases a little potassium from cells. |
| Electrolytes, Na/K/Cl | mmol/L | A grouped heading on some reports. Each electrolyte beneath it is a separate result with its own range. |
Potassium is also measured in urine, where the result answers a different question about how much the kidneys are passing. A urine value is not comparable with a blood value.
Why this page does not print a range
Reference ranges are built by laboratories for their own methods and populations. Potassium ranges can differ between laboratories and analysers, between age groups and between sexes, and in pregnancy. The sample matters too: a haemolysed sample, a delayed sample, or a sample from an arm with a line running can produce a value the laboratory knows to flag.
The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result and does not replace it with a general range from the internet. If the report carries a comment about the sample, read it with the number.
What a high value can mean
A result above the report's range means the potassium concentration in the sample is higher than the laboratory's reference interval. The term hyperkalaemia describes a high potassium concentration; it names the finding, not a diagnosis.
Possible contributors include reduced kidney excretion; medicines such as ACE inhibitors, angiotensin receptor blockers, potassium-sparing diuretics, and some anti-inflammatory medicines; adrenal insufficiency; acidosis; and the release of potassium from damaged cells, as in haemolysis, muscle breakdown, or the rapid breakdown of tumour cells. A haemolysed or delayed sample can also raise the measured value without any change in the body. The result does not confirm or rule out any of these.
What a low value can mean
A result below the report's range means the potassium concentration is lower than the laboratory's interval. The term hypokalaemia describes the finding. A low value is often not meaningful on its own, but it can reflect a real shift in potassium balance and is read with the rest of the panel.
Possible contributors include loss through the gut, as with vomiting, diarrhoea, or laxative use; loss through the kidneys, as with some diuretics, some antibiotics, or a hormone condition such as hyperaldosteronism; a shift of potassium into cells, as with insulin or some asthma medicines; and a low magnesium result, which often accompanies low potassium. A low dietary intake alone is a less common explanation in a person who is otherwise well.
What can move the value
- Sample handling. Red cells release potassium, so haemolysis, a delay before processing, or a sample from a line can raise the result.
- Collection technique. Prolonged fist clenching or a tourniquet left in place can raise the measured value.
- Time of day. Potassium tends to be higher in the morning and lower later in the day.
- Medicines. Diuretics, blood pressure medicines, some antibiotics, insulin, and some asthma medicines can change potassium handling or shift it between compartments.
- Acid-base balance. Changes in blood acidity move potassium into or out of cells.
- Blood cell counts. Very high platelet or white cell counts can release potassium into serum after collection.
What to compare it with
Read potassium with sodium, chloride, and bicarbonate on the same panel; with magnesium and calcium, which affect how potassium behaves; with urea and creatinine for the kidney view; and with glucose, because insulin shifts potassium into cells. The trend across reports from the same laboratory is usually more informative than a single value.
How to see the trend
Doctano reads the potassium value, its unit, and the reference range printed on the report. It keeps the range with the result, normalizes the marker name across laboratories, and places the value on the profile's timeline. Each point still opens the report it came from, so a comment about haemolysis or a repeat sample stays attached to the number it describes.
Verify the value and the unit against the original report before treating a change as real, especially when the two results came from different laboratories or were collected under different conditions.
What this page is not
This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.