What this test measures
A Serum Electrolytes panel typically measures sodium (Na+), potassium (K+), chloride (Cl-) and bicarbonate (HCO3-). These ions regulate body fluid balance, nerve and muscle function, and acid-base status. Imbalances can cause symptoms ranging from mild (cramps, fatigue) to life-threatening (cardiac arrhythmias, seizures, coma).
Why it matters
Electrolyte panels are part of every Kidney Function Test and are ordered whenever there are symptoms of fluid imbalance (vomiting, diarrhoea, swelling), kidney problems, blood-pressure changes, hospitalisation, and to monitor people on diuretics, ACE inhibitors, ARBs, lithium, or chemotherapy. Electrolyte imbalances are common in elderly Indian adults, in people with CKD, in heart failure, and in any acute illness with vomiting / diarrhoea.
How to prepare
No fasting required. Stay normally hydrated. Continue medications unless your doctor instructs otherwise; mention any diuretics, ACE-i/ARBs, NSAIDs, lithium or recent IV fluids. Avoid clenching your fist during the blood draw — it can falsely raise potassium.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Sodium (Na+) (mEq/L)[1] | 135 – 145 | Hyponatraemia (<135). Causes: heart failure, cirrhosis, SIADH (post-surgery, lung disease, drugs), diuretics, vomiting / diarrhoea, excessive water intake. Symptoms: nausea, confusion, seizures (<120). Correction must be gradual to avoid central pontine myelinolysis. | Hypernatraemia (>145). Almost always dehydration — inadequate water intake (elderly, infants), diabetes insipidus, large insensible losses. Symptoms: thirst, dry mucous membranes, confusion. Re-hydrate carefully. |
| Potassium (K+) (mEq/L) | 3.5 – 5.0 | Hypokalaemia. Causes: diuretics (thiazide, loop), vomiting, diarrhoea, low intake, magnesium deficiency, hyperaldosteronism. Symptoms: weakness, cramps, palpitations. Severe (<2.5) — urgent, risk of arrhythmias. | Hyperkalaemia. Causes: acute kidney injury, CKD, ACE inhibitors / ARBs, spironolactone, potassium supplements, severe tissue breakdown. Above 6.0 — dangerous arrhythmia risk, needs urgent treatment. |
| Chloride (Cl-) (mEq/L) | 98 – 107 | Hypochloraemia. Often parallels hyponatraemia. Vomiting, diuretics, CKD, metabolic alkalosis. | Hyperchloraemia. Dehydration, hyperaldosteronism, diabetes insipidus, large saline infusions, metabolic acidosis. |
| Bicarbonate (HCO3-) (mEq/L) | 22 – 28 | Metabolic acidosis. Causes: diabetic ketoacidosis, lactic acidosis (sepsis, shock), diarrhoea, CKD, drug toxicities. Pair with arterial blood gas if severe. | Metabolic alkalosis. Vomiting, diuretics, hypokalaemia, hyperaldosteronism. |
Common electrolyte derangements
| Imbalance | Common causes | Action |
|---|---|---|
| Hyponatraemia (Na <135) | Diuretics, heart failure, cirrhosis, SIADH, excessive water | Correct gradually; address underlying cause |
| Hypernatraemia (Na >145) | Dehydration, diabetes insipidus | Re-hydrate; correct gradually |
| Hypokalaemia (K <3.5) | Diuretics, vomiting, diarrhoea, low intake | Oral or IV potassium; check magnesium |
| Hyperkalaemia (K >5.0) | CKD, ACE-i/ARB, spironolactone, K supplements | Stop offending drugs; calcium gluconate + insulin-dextrose if >6.0 with ECG changes |
| Metabolic acidosis (HCO3 <22) | DKA, lactic acidosis, CKD, diarrhoea | Identify cause; treat underlying |
| Metabolic alkalosis (HCO3 >28) | Vomiting, diuretics, hypokalaemia | Saline + potassium replacement |
Frequently asked questions
Do I need to fast for serum electrolytes?
No fasting required. Continue medications unless your doctor advises otherwise.
My potassium is 5.5 — should I worry?
Mild hyperkalaemia (5.1–5.5) is sometimes seen with delayed sample processing or hemolysis (red cell breakdown in the tube). Repeat promptly. If genuinely elevated and you are on an ACE inhibitor / ARB / spironolactone, your doctor may adjust the dose.
My sodium is 132 — is that dangerous?
Mild hyponatraemia (130–134) is common and usually mild. Acute drops or values below 125 can cause confusion, seizures and need urgent attention. The cause matters — your doctor will look at fluid status and medications.
Why did my potassium come back high but I feel fine?
A common cause of falsely raised potassium is hemolysis in the blood tube (often from fist clenching, prolonged tourniquet, or delayed processing). If symptoms do not match the value, repeat the test in a fresh sample before treating.
Can diet alone raise or lower potassium dangerously?
In healthy people, no — kidneys efficiently excrete excess potassium. In CKD or on ACE inhibitors / spironolactone, high-potassium foods (banana, coconut water, citrus, tomatoes, spinach, dates) can push potassium into the danger zone. Diuretics + low-potassium diet can drop it.
How often should I check electrolytes?
Annually as part of a routine KFT in adults with risk factors. Every 1–2 weeks initially after starting or adjusting diuretics, ACE inhibitors, ARBs or spironolactone, then every 3–6 months once stable. More often in CKD or active illness.
Should I do electrolytes alone or a full KFT?
A full KFT includes electrolytes plus creatinine, BUN, uric acid, calcium, phosphorus and eGFR — usually preferred for the same blood draw. Standalone electrolytes are useful for short-interval monitoring (e.g. after starting a diuretic).
Related Kidney / Electrolytes tests
Tests commonly ordered alongside SERUM ELECTROLYTES, or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Electrolyte Panel · accessed 2026-05-29T00:00:00.000Z
- NCBI StatPearls — Electrolytes · accessed 2026-05-29T00:00:00.000Z
- KDIGO 2024 CKD Guideline · accessed 2026-05-29T00:00:00.000Z
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