Potassium 5.2 mmol/L — borderline hyperkalaemia
Serum potassium of 5.2 mmol/L sits just above the standard reference range (3.5-5.1 mmol/L). The most common cause of mild hyperkalaemia on a single draw is haemolysis artefact — red blood cells lyse during phlebotomy or transport, releasing intracellular potassium and falsely elevating the reading. Lab reports flag this when haemolysis is detected. Persistent true elevation has a short differential: renal insufficiency (impaired excretion), medications (ACE inhibitors, ARBs, potassium-sparing diuretics, NSAIDs), adrenal insufficiency (Addison's), and acidosis. Severe hyperkalaemia (>6.5 mmol/L) is a cardiac emergency due to membrane depolarisation and arrhythmia risk.
Reference ranges
| Standard reference | 3.5 – 5.1 mmol/L |
| Borderline elevation | 5.1 – 5.5 mmol/L |
| Moderate hyperkalaemia | 5.5 – 6.5 mmol/L |
| Severe (cardiac emergency) | > 6.5 mmol/L |
What this marker measures
Potassium is the dominant intracellular cation; serum levels reflect a tiny fraction of total body potassium but are tightly regulated because the membrane potential of all cells (especially cardiac) depends on the K+ gradient. Renal excretion adjusts to dietary intake within hours-days. Aldosterone is the major hormonal regulator — it stimulates renal potassium excretion. Elevated serum K+ usually means impaired excretion, not excessive intake.
Why might it be elevated?
- ·Haemolysis artefact (most common — single-draw)
- ·Renal insufficiency (any cause)
- ·ACE inhibitors, ARBs, potassium-sparing diuretics (spironolactone, eplerenone)
- ·NSAIDs (especially with renal insufficiency)
- ·Addison disease / adrenal insufficiency
- ·Type 4 renal tubular acidosis
- ·Tissue breakdown (rhabdomyolysis, tumour lysis)
- ·Heparin therapy
Why might it be low?
- ·Diuretic use (loop, thiazide)
- ·GI losses (vomiting, diarrhoea)
- ·Hypomagnesaemia
- ·Hyperaldosteronism (Conn syndrome)
- ·Eating disorders
- ·Diabetic ketoacidosis (insulin shifts K+ intracellular)
FAQ
Should I worry about 5.2?+
If a one-off, almost always haemolysis. Repeat the draw with care — and check the lab report for haemolysis flagging. If persistently elevated across multiple clean draws, get renal function (creatinine, eGFR) and review medications with a clinician.
Should I cut bananas?+
Almost never. Dietary potassium intake adjusts via renal excretion in healthy individuals. Cutting bananas or other potassium-rich foods is only relevant if you have chronic kidney disease (CKD stage 3-5) where excretion is compromised — in which case you'd be working with a renal dietitian, not Reddit.
This page describes biomarker research and reference ranges for self-tracking and research-context discussion only. It is not medical advice, not a diagnosis, and not a substitute for a qualified physician. Take any concerns about your health to a clinician.
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