Quick Answer
Electrolyte disorders contribute 2–3 NEET PG questions per paper across Medicine, Nephrology, and Emergency Medicine. The high-yield framework:
- Hyponatremia — measure osmolality first, then assess volume status, then check urine sodium. SIADH is euvolemic; cerebral salt wasting is hypovolemic.
- Hypernatremia — almost always reflects free water deficit. Calculate deficit, replace slowly (no faster than 10 mEq/L/24 hr).
- Hyperkalemia — peaked T-waves to sine wave; calcium gluconate first if ECG changes, then insulin-glucose, then potassium removal.
- Hypokalemia — U-waves, T-flattening, ventricular ectopy; correct magnesium simultaneously or potassium will not rise.
- Hypocalcemia — Trousseau, Chvostek, prolonged QT; treat with IV calcium gluconate if symptomatic.
- Hypercalcemia — bones, stones, groans, psychic moans; aggressive saline plus calcitonin then bisphosphonate.
Electrolyte disorders sit at the intersection of physiology, nephrology, and emergency medicine — which is exactly why they appear so often on NEET PG. Examiners love stem-and-table problems where a single lab value (urine sodium, serum osmolality, calculated osmolar gap) pivots the entire diagnosis. Mastering electrolytes is less about memorising ranges and more about following a disciplined diagnostic algorithm under time pressure.
This NEETPGAI deep dive walks through the six most testable electrolyte disturbances, the workup steps examiners expect, the ECG and bedside signs that anchor diagnosis, and the management ladders that frequently turn up as drag-and-drop or sequential-step questions. Pair this with hands-on MCQs from the Medicine subject hub and the acid-base disorders guide for full electrolyte-and-ABG fluency.
Hyponatremia — the most testable electrolyte
Hyponatremia (serum sodium below 135 mEq/L) is the commonest electrolyte disorder in hospital practice and the single most common electrolyte question on NEET PG. The trick is the algorithm: osmolality, then volume, then urine.
Step 1 — Measure serum osmolality
- Hypotonic hyponatremia (osm <275) — true hyponatremia; classify by volume status.
- Isotonic hyponatremia (275–295) — pseudohyponatremia from hyperlipidemia or hyperproteinemia.
- Hypertonic hyponatremia (osm >295) — hyperglycemia or mannitol pulls water out of cells. Correct sodium rises by 1.6 mEq/L per 100 mg/dL glucose above 100.
Step 2 — Assess volume status
| Volume status | Likely causes | Urine Na |
|---|
| Hypovolemic | Diarrhea, vomiting, diuretics, third-spacing, salt-wasting nephropathy, Addison disease, cerebral salt wasting | <20 if extra-renal loss, >20 if renal loss |
| Euvolemic | SIADH, hypothyroidism, glucocorticoid deficiency, primary polydipsia, beer potomania | >40 (SIADH) |
| Hypervolemic | CHF, cirrhosis, nephrotic syndrome, advanced CKD | <20 (CHF, cirrhosis); >20 (renal failure) |
SIADH vs cerebral salt wasting — the classic trap
Both produce hyponatremia with urine sodium >40 mEq/L and high urine osmolality. Volume status decides. SIADH is euvolemic and responds to fluid restriction. Cerebral salt wasting (CSW) is hypovolemic after subarachnoid hemorrhage or TBI and worsens with fluid restriction — it requires salt plus volume replacement (3% saline or hypertonic). Mistaking CSW for SIADH and restricting fluids has been an INI-CET stem.
Treatment of hyponatremia
- Severe symptoms (seizure, coma, herniation): 3% hypertonic saline 100 mL bolus, repeat up to 3 times until symptoms resolve.
- Asymptomatic chronic: treat the cause; rate of correction must not exceed 8–10 mEq/L in 24 hr and 18 mEq/L in 48 hr to avoid osmotic demyelination syndrome (formerly central pontine myelinolysis).
- SIADH-specific: fluid restriction first; tolvaptan (vaptan) for refractory cases; demeclocycline largely historical.
- High-risk groups for ODS: chronic alcoholics, malnourished patients, hypokalemia, liver disease.
Hypernatremia — a free water problem
Hypernatremia (serum sodium >145 mEq/L) almost always reflects water loss exceeding sodium loss, often in patients who cannot access water (elderly, intubated, infants).
- Causes: insensible losses, osmotic diuresis (hyperglycemia, mannitol), diabetes insipidus (central or nephrogenic), inadequate intake.
- Diabetes insipidus split: water deprivation test then desmopressin challenge — desmopressin response confirms central DI; no response = nephrogenic DI (lithium, hypercalcemia, hypokalemia).
- Free water deficit (L) = 0.6 × weight × ((Na/140) − 1) for men; use 0.5 for women and elderly.
- Correction rate: <10 mEq/L/24 hr; faster correction causes cerebral edema and seizures.
- Use D5W or oral water; isotonic saline is appropriate only if shock-volume resuscitation is needed first.
Hyperkalemia — the ECG-driven emergency
Hyperkalemia (K >5.0 mEq/L) is the most lethal electrolyte disturbance and a near-certain NEET PG topic. The ECG progression is examined repeatedly: peaked T-waves → PR prolongation → P-wave loss → QRS widening → sine wave → VF/asystole.
Causes
- Pseudohyperkalemia (hemolysis, severe leukocytosis or thrombocytosis) — repeat the sample.
- Decreased excretion: AKI, CKD, type 4 RTA (hypoaldosteronism), adrenal insufficiency, ACEi/ARB/ARNI, spironolactone, eplerenone, trimethoprim, NSAIDs, heparin (suppresses aldosterone).
- Cellular shift: acidosis, insulin deficiency (DKA), tumor lysis, rhabdomyolysis, succinylcholine in burns or denervation, beta-blocker overdose, digoxin toxicity.
Management ladder (in order)
- Calcium gluconate 10 mL of 10% IV over 2–3 min — stabilises the myocardium within minutes; does NOT lower potassium. Repeat if ECG abnormalities persist.
- Insulin 10 U IV plus 25 g dextrose — shifts K into cells in 15–30 min. Lasts 4–6 hr.
- Beta-2 agonist (nebulised salbutamol 10–20 mg) — additional shift; synergistic with insulin.
- Sodium bicarbonate — only if metabolic acidosis present.
- Removal: loop diuretics (furosemide), patiromer or sodium zirconium cyclosilicate (oral, slower), and hemodialysis if refractory or in oliguric AKI.
- Avoid Kayexalate (sodium polystyrene sulfonate) — recent guidelines deprecate it due to colonic necrosis risk.
Hypokalemia — replace magnesium too
Hypokalemia (K <3.5 mEq/L) is rarely life-threatening but a common cause of arrhythmia, especially with concurrent digoxin therapy.
- ECG: flattened T-waves, prominent U-waves, ST depression, ventricular ectopy, torsades de pointes.
- Causes: GI losses (vomiting, diarrhea), diuretics (loop, thiazide), Bartter and Gitelman syndromes, primary aldosteronism, Cushing syndrome, hypomagnesemia, insulin therapy, beta-2 agonists, refeeding syndrome.
- Spot urine potassium: <20 mEq/L = extra-renal loss; >20 mEq/L = renal loss.
- Replacement: 10 mEq oral KCl raises serum K by ~0.1 mEq/L; IV no faster than 10 mEq/hr peripheral or 20 mEq/hr central with cardiac monitoring.
- Critical pearl: correct hypomagnesemia simultaneously — magnesium-deficient patients waste potassium renally and will not retain repleted K until magnesium is normal.
Hypocalcemia — neuromuscular irritability
Total calcium <8.5 mg/dL or ionised <4.5 mg/dL. Always correct for albumin: corrected Ca = measured Ca + 0.8 × (4 − albumin).
- Causes: hypoparathyroidism (post-thyroidectomy is the classic NEET PG stem), vitamin D deficiency, CKD, hypomagnesemia, acute pancreatitis, tumor lysis syndrome, massive transfusion (citrate chelation), pseudohypoparathyroidism (Albright hereditary osteodystrophy).
- Signs: Trousseau (carpal spasm after BP cuff inflation), Chvostek (facial twitch), perioral paresthesia, tetany, laryngospasm, seizures, prolonged QT, heart failure.
- Management:
- Symptomatic or QT prolonged: IV calcium gluconate 10 mL of 10% over 10 min, then infusion.
- Asymptomatic: oral calcium plus vitamin D (calcitriol if PTH or kidney problem).
- Always check and correct magnesium — hypomagnesemia causes functional hypoparathyroidism.
Hypercalcemia — bones, stones, groans, psychic moans
Calcium >10.5 mg/dL. The two-cause rule covers 90% of cases: primary hyperparathyroidism (outpatient) and malignancy (inpatient).
| Feature | Primary hyperparathyroidism | Malignancy-associated |
|---|
| PTH | Elevated or inappropriately normal | Suppressed |
| PTHrP | Normal | Elevated (squamous cancers) |
| Phosphate | Low | Variable |
| Onset | Insidious | Acute, severe |
| Common stem | Asymptomatic, found on routine labs | Breast, lung, multiple myeloma |
Other causes worth knowing
- Vitamin D toxicity, sarcoidosis (granulomatous activation of 1-α-hydroxylase), thiazides, lithium, milk-alkali syndrome, immobilisation, familial hypocalciuric hypercalcemia (low urine calcium-to-creatinine ratio <0.01 — do not parathyroidectomize).
Treatment ladder
- Aggressive isotonic saline 200–300 mL/hr — restores volume and promotes calciuresis. Cornerstone of acute therapy.
- Calcitonin 4 U/kg SC every 12 hr — fast onset, tachyphylaxis after 48 hr.
- Bisphosphonate (zoledronate 4 mg IV) — definitive but takes 2–4 days to peak.
- Denosumab — for refractory or in renal failure.
- Hemodialysis — life-threatening or anuric.
- Glucocorticoids — granulomatous, lymphoma, vitamin D toxicity.
High-yield NEET PG MCQ traps
- Hyponatremia correction overshoot — chronic alcoholic with Na 110 corrected to 130 in 24 hr develops locked-in syndrome (osmotic demyelination). Cap at 8–10 mEq/L/24 hr.
- Pseudohyponatremia clue — triglycerides >1000 or paraproteinemia. Sodium is normal; do not treat.
- Calcium gluconate vs chloride — gluconate preferred peripherally; chloride causes severe extravasation injury.
- Magnesium-resistant hypokalemia — refractory K replacement until Mg replaced. Classic in chronic diuretic users.
- Hyperkalemia ECG order — peaked T first; sine wave is pre-arrest.
- Pseudohypoparathyroidism (Albright) — short stature, brachydactyly (short 4th and 5th metacarpals), round face, with low Ca, high PO4, high PTH. End-organ resistance.
- Hypocalcemia after thyroidectomy — early hypocalcemia from inadvertent parathyroidectomy is the highest-yield post-op vignette. Watch for stridor (laryngospasm).
- Familial hypocalciuric hypercalcemia (FHH) — calcium-sensing receptor mutation; spuriously elevated calcium with low urine calcium. Avoid surgery.
Recent updates and Indian context
- KDIGO 2024 retains tolvaptan for SIADH refractory to fluid restriction but warns about hepatotoxicity in ADPKD use.
- Endocrine Society 2023 revised primary aldosteronism screening — aldosterone-renin ratio remains gold standard but cutoffs adjusted.
- NICE 2024 electrolyte replacement guidelines: prefer enteral over parenteral whenever possible; reserve IV potassium for symptomatic or severe deficits.
- Indian context: rural India sees disproportionate diuretic-induced hypokalemia (loop and thiazide combos), refeeding syndrome in TB patients re-initiating nutrition, and hyponatremia in elderly on SSRIs and thiazides — common FMGE and NEET PG vignette setups.
Frequently asked questions
What is the first step in evaluating hyponatremia?
After excluding pseudohyponatremia, measure serum osmolality first. True (hypotonic) hyponatremia has serum osmolality below 275 mOsm/kg. Then assess volume status clinically and measure urine osmolality and urine sodium to classify as hypovolemic, euvolemic, or hypervolemic — a NEET PG favourite stepwise approach.
How do you differentiate SIADH from cerebral salt wasting?
Both show hyponatremia with high urine sodium, but volume status differs. SIADH is euvolemic with normal or expanded volume, while cerebral salt wasting (CSW) is hypovolemic with signs of dehydration. SIADH responds to fluid restriction; CSW needs salt and volume replacement — fluid restriction worsens it.
What are the ECG changes in hyperkalemia in order?
Earliest change is peaked T-waves (above 5.5 mEq/L), then PR prolongation, P-wave flattening, QRS widening, sine-wave pattern, and finally ventricular fibrillation or asystole. Calcium gluconate is given first when ECG changes are present — it stabilises the myocardium within minutes without lowering potassium.
What is the maximum safe correction rate for chronic hyponatremia?
Correct serum sodium by no more than 8 to 10 mEq/L in 24 hours and 18 mEq/L in 48 hours. Faster correction risks osmotic demyelination syndrome (central pontine myelinolysis), particularly in chronic alcoholics, malnourished patients, and hypokalemic patients. Use hypertonic saline cautiously with frequent sodium checks.
Which electrolyte disorder causes Trousseau and Chvostek signs?
Hypocalcemia causes both. Trousseau sign is carpal spasm after BP cuff inflation above systolic for 3 minutes; Chvostek sign is facial twitch on tapping the facial nerve. Both reflect neuromuscular hyperexcitability from low ionised calcium and are classic NEET PG vignette clues.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: April 2026
