Potassium Blood Test: Dangerous Levels and What Causes Them

Causes of High Potassium (Hyperkalaemia)

Causes of Low Potassium (Hypokalaemia)

Potassium vs sodium vs magnesium vs calcium: how they compare

Potassium is the most urgently dangerous electrolyte when abnormal — but each electrolyte tells a different story:

Potassium and magnesium are checked together for a reason — and potassium's urgency comes from the heart, which is why ECG changes are part of the assessment.

Reading your report: what your doctor actually looks at

When a doctor opens a potassium result, the first question is whether it's real. Here is the checklist they run through — and the same checklist helps you read your own report calmly:

1. Was the sample clean? Haemolysis (burst red cells), a tight tourniquet, fist-clenching during the draw — all fake high potassium. An unexpected high value is repeated before anyone worries; pseudohyperkalaemia is common.
2. Is it slightly or seriously off? Small deviations near the 3.5–5.0 mmol/L range edge are often transient — the distance from the range and the symptoms decide urgency, not the flag alone.
3. What medicines are on board? ACE inhibitors, spironolactone, trimethoprim and NSAIDs raise potassium; thiazide and loop diuretics lower it. The prescription list is half the interpretation.
4. What are the kidneys doing? The kidneys excrete potassium — kidney disease is the commonest cause of genuine high potassium, and the eGFR is always checked alongside.
5. Any symptoms or ECG changes? Muscle weakness, and the characteristic ECG changes of high potassium, are what convert a number into an emergency — symptoms plus value, never value alone. Discuss the full picture with your doctor.

Potassium's rule: repeat the surprising high before believing it, review the medicines, check the kidneys — and treat symptoms and ECG changes as the emergency criteria. Discuss the full picture with your doctor.

Potassium test price in India: typical bands across major lab chains

Potassium is a cheap, routine chemistry test — almost always part of a panel rather than ordered alone. Typical list-price bands:

These are approximate bands, not quotes: prices change often and vary by city, and home collection can add a small fee. Where possible, choose a NABL-accredited lab, and remember the reference range printed on your own report is the one that counts.

Frequently Asked Questions

Pharmacist's practical notes

The drug list is potassium's Rosetta stone: ACE inhibitors and spironolactone push it up, thiazides and loop diuretics push it down — and the combination of an ACE inhibitor with spironolactone is the classic high-potassium setup. Every new abnormal value deserves a prescription review first.

Salt substitutes are potassium chloride — “low-sodium salt” can meaningfully raise potassium, especially with kidney disease or potassium-raising medicines. It's the dietary source nobody counts. And never adjust prescribed diuretics or ACE inhibitors over a lab value without medical advice.

In India

Indian labs report potassium in mmol/L, which is numerically identical to mEq/L — the usual range of 3.5–5.0 mmol/L applies. The test typically costs &rupee;200–&rupee;400, though prices vary by city and lab.

Where possible, choose a NABL-accredited lab. An unexpected high value should be repeated — sample-related false highs are common.

References

Sources cited on this page. PubMed links open the original abstract.

1. Weiner ID, Wingo CS. Hypokalemia–consequences, causes, and correction. J Am Soc Nephrol. 1997;8(7):1179–1188. PMID 9219169 · doi:10.1681/ASN.V871179
2. Le Goff E, Jondeau K, Venon MD, et al. Pseudohyperkalemia and thrombocytosis. Rev Med Interne. 2021;42(6):438–441. PMID 33531232 · doi:10.1016/j.revmed.2020.12.008
3. Reiser IW, Chou SY, Brown MI, Porush JG. Reversal of Trimethoprim-Induced Antikaliuresis. Kidney Int. 1996;50(6):2063–2069. PMID 8943491 · doi:10.1038/ki.1996.530

Why a high potassium is sometimes not real

Pseudohyperkalaemia is common enough that it should always be considered before acting on an unexpectedly high result in someone who feels well. Potassium sits mostly inside cells, so anything that damages cells between the vein and the analyser releases it into the sample. Prolonged tourniquet time, clenching the fist repeatedly during the draw, a difficult collection through a narrow needle, delayed transport, and samples chilled or shaken all raise the measured value.² A very high platelet count does the same thing by a different route: platelets release potassium as the sample clots, so a serum result can read high while the true level is normal. In one series, three patients with marked thrombocytosis had serum potassium between 6.1 and 7.7 mmol/L, yet repeat testing on heparinised samples came back at 4.4 to 4.6 mmol/L and no treatment was needed.² A very high platelet or white cell count can do the same. If a raised potassium does not fit the clinical picture, the standard response is to repeat it with careful technique before starting treatment.

Medications that raise potassium

• ACE inhibitors and ARBs, among the most frequent causes in routine practice.
• Potassium-sparing diuretics such as spironolactone, eplerenone and amiloride.
• NSAIDs, which reduce renal perfusion and compound the effect of the above.
• Trimethoprim, including in co-trimoxazole, which acts on the same renal channel as amiloride: it blocks the amiloride-sensitive sodium channel in the distal nephron, reducing potassium secretion by the same route.³
• Heparin, and potassium-containing salt substitutes, which people often do not think of as medicines.

Why potassium and magnesium travel together

A low potassium that will not correct despite replacement is frequently a magnesium problem. Magnesium depletion promotes renal potassium wasting, and until the magnesium is replaced the potassium continues to leak. This is a routine consideration in people on long-term diuretics, with alcohol dependence, or with significant diarrhoea, and it is why magnesium is often checked alongside a persistently low potassium rather than after several failed attempts at replacement.

Symptoms and why they are unreliable

Both high and low potassium can produce muscle weakness, cramps and palpitations, and both can be completely silent until the level is dangerous. Because the heart is the organ at risk, an ECG is often more informative than symptoms: peaked T waves, a widening QRS and loss of P waves indicate hyperkalaemia needing immediate treatment, while flattened T waves and prominent U waves suggest hypokalaemia. The absence of ECG changes does not make a markedly abnormal potassium safe to ignore.