Reference — Electrolytes
Electrolyte Reference Ranges
Normal reference ranges for the six electrolytes most critical to nursing practice — sodium, potassium, calcium, magnesium, phosphorus, and chloride — with critical value thresholds and bedside clinical notes.
Educational use only. Reference ranges may vary slightly by laboratory. Always use the institution-specific reference intervals printed on laboratory reports. Critical values require immediate provider notification. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Electrolyte Normal Ranges at a Glance
| Electrolyte | Normal Range | Units | Critical Low | Critical High |
|---|---|---|---|---|
| Sodium (Na⁺) | 136 – 145 | mEq/L | < 120 | > 160 |
| Potassium (K⁺) | 3.5 – 5.0 | mEq/L | < 2.5 | > 6.5 |
| Calcium (Ca²⁺) — Total | 8.5 – 10.5 | mg/dL | < 7.0 | > 13.0 |
| Calcium (Ca²⁺) — Ionized | 4.5 – 5.5 | mg/dL | < 3.5 | > 6.5 |
| Magnesium (Mg²⁺) | 1.7 – 2.2 | mg/dL | < 1.0 | > 4.9 |
| Phosphorus (PO₄³⁻) | 2.5 – 4.5 | mg/dL | < 1.0 | > 8.0 |
| Chloride (Cl⁻) | 98 – 106 | mEq/L | < 80 | > 115 |
Critical values are general thresholds — specific institutions may define critical values differently. Always follow the laboratory report reference intervals and institutional critical value policy.
Clinical Notes by Electrolyte
Sodium (Na⁺) — The Osmolality Regulator
Sodium is the major extracellular cation and the primary determinant of plasma osmolality. Changes in sodium reflect fluid balance more than total body sodium content. Hyponatremia is the most common electrolyte disorder in hospitalized patients. Rapid correction of either hyponatremia or hypernatremia can cause severe neurological complications — correct slowly (maximum 8–10 mEq/L per 24 hours).
Potassium (K⁺) — The Cardiac Electrolyte
Potassium is the major intracellular cation. Small changes in serum potassium produce significant effects on cardiac conduction, muscle function, and nerve transmission. The narrow normal range (3.5–5.0 mEq/L) reflects its sensitivity. Potassium shifts out of cells in acidosis (raising serum K⁺) and into cells in alkalosis (lowering serum K⁺). Always check and replace magnesium concurrently when replacing potassium.
Calcium (Ca²⁺) — Total vs Ionized
Total calcium includes protein-bound and free (ionized) calcium. Ionized calcium is the physiologically active form. In hypoalbuminemia, total calcium is falsely low — correct for albumin: corrected Ca = measured Ca + 0.8 × (4.0 − measured albumin). Alkalosis decreases ionized calcium (protein binding increases), causing symptomatic hypocalcemia even when total calcium is normal.
Magnesium (Mg²⁺) — The Hidden Electrolyte
Magnesium is frequently under-checked. Hypomagnesemia causes refractory hypokalemia and hypocalcemia — both cannot be corrected until magnesium is repleted. In hypermagnesemia from eclampsia treatment, monitor patellar reflex (loss precedes respiratory depression) and maintain serum Mg below 8 mg/dL. Antidote for both hyperkalemia and hypermagnesemia: calcium gluconate.
Phosphorus (PO₄³⁻) — Inverse Relationship with Calcium
Phosphorus and calcium have an inverse relationship regulated by parathyroid hormone (PTH). Hyperphosphatemia is common in chronic kidney disease (CKD) — phosphate binders are used to manage it. Hypophosphatemia occurs in refeeding syndrome, DKA treatment, alcoholism, and malabsorption. Severe hypophosphatemia (< 1.0 mg/dL) causes muscle weakness, respiratory failure, and hemolytic anemia.
Chloride (Cl⁻) — Acid-Base Partner
Chloride is the major extracellular anion and moves inversely with bicarbonate to maintain electroneutrality. Hypochloremia often accompanies metabolic alkalosis (vomiting, NG suction — HCl loss). Hyperchloremia from large volumes of normal saline can cause hyperchloremic metabolic acidosis. The anion gap calculation requires sodium and chloride: AG = Na⁺ − (Cl⁻ + HCO₃¹); normal AG = 8–12 mEq/L.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with Infusion Nurses Society (INS) Standards of Practice · Institute for Safe Medication Practices (ISMP) · Standard laboratory reference ranges. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →