NCLEX electrolytes cheat sheet: sodium, potassium, calcium, magnesium and phosphate — normal ranges, signs of imbalance, and what the nurse does first.
Hyponatremia (Na⁺ <135)
| Signs | confusion, headache, cramps, seizures, N/V |
| Causes | SIADH, excess water, diuretics, vomiting |
| Treat | fluid restriction; 3% saline (severe, SLOW) |
Correct slowly (osmotic demyelination).
Hypernatremia (Na⁺ >145)
| Signs | thirst, agitation, dry mucosa, seizures |
| Causes | water loss, DI, ↑Na intake, fever |
| Treat | water (hypotonic IV slow); restrict Na |
Think 'salty & dry.'
Hypokalemia (K⁺ <3.5)
| Signs | weakness, flat T/U wave, ileus, dysrhythmia |
| Causes | diuretics, vomiting, NG suction, insulin |
| Treat | replace K⁺ — NEVER IV push, on a pump |
Ensure urine output before replacing.
Hyperkalemia (K⁺ >5.0)
| Signs | peaked T, wide QRS, weakness, arrest |
| Causes | renal failure, K-sparing diuretics, acidosis |
| Treat | Ca gluconate, insulin+D50, kayexalate, dialysis |
Ca gluconate protects the heart first.
Hypocalcemia (Ca²⁺ <9)
| Signs | +Chvostek/Trousseau, tetany, ↑DTR, spasm |
| Causes | hypoparathyroid, thyroidectomy, ↓vit D |
| Treat | calcium; vitamin D; airway/seizure precautions |
Tetany + tingling = low calcium.
Hypercalcemia (Ca²⁺ >10.5)
| Signs | weakness, ↓DTR, stones, constipation, confusion |
| Causes | hyperparathyroid, malignancy, immobility |
| Treat | IV fluids + loop diuretic; bisphosphonates |
'Bones, stones, groans, moans.'
Hypomagnesemia (Mg²⁺ <1.5)
| Signs | tremor, hyperreflexia, +Chvostek, torsades |
| Causes | alcohol use, malnutrition, diarrhea, diuretics |
| Treat | replace Mg; monitor cardiac rhythm |
Mirrors low calcium; common in alcohol use.
Hypermagnesemia (Mg²⁺ >2.5)
| Signs | ↓DTR, hypotension, bradycardia, resp depression |
| Causes | renal failure, Mg antacids, OB mag therapy |
| Treat | stop Mg; calcium gluconate (antidote); fluids |
Loss of reflexes = early warning.
Key Rules
| Ca ↔ Phos | inversely related (one up, other down) |
| Mg & Ca | behave alike (both low = tetany) |
| K⁺ & Ca²⁺ | extremes = cardiac monitoring priority |
Educational quick-reference only; values/ranges vary by source. Verify against your facility and the current NCSBN test plan.
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