Reference — Electrolytes
Calcium Regulation Reference
Three hormones, three organs, one number. Once you know that PTH and vitamin D raise calcium and calcitonin lowers it— and that calcium and phosphate move in opposite directions — every calcium and parathyroid disorder becomes predictable.
Educational use only. This is a conceptual reference for interpreting calcium values; ranges and treatment are provider- and facility-specific. 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.
The Three Regulators
| Hormone | Effect on Ca | How |
|---|---|---|
| Parathyroid hormone (PTH) | RAISES calcium | Pulls Ca from bone, reabsorbs Ca (and wastes phosphate) in kidney, activates vitamin D |
| Vitamin D (calcitriol) | RAISES calcium | Increases Ca AND phosphate absorption from the gut; activated by PTH and the kidney |
| Calcitonin | LOWERS calcium | From the thyroid C-cells; deposits Ca into bone, lowers serum Ca (minor everyday role) |
The Calcium-Phosphate Inverse
Calcium and phosphate have a reciprocal (seesaw) relationship: when one rises, the other falls. PTH raises calcium and wastes phosphate in the urine, reinforcing the seesaw. Clinically: hyperparathyroidism → high Ca, low phosphate; CKD → high phosphate, low Ca (driving secondary hyperparathyroidism).
Ionized vs Total & the Albumin Correction
About half of serum calcium is bound to albumin; the rest is the active ionized (free) calcium. A standard lab reports total calcium, so a low albumin makes total calcium look low even when the active ionized level is normal. Correct it or order an ionized calcium.
A common bedside correction: add 0.8 mg/dL to total calcium for every 1 g/dL the albumin is below 4 g/dL. Ionized calcium is the most accurate measure and is preferred in critical illness, transfusion, and acid-base shifts (acidosis raises ionized Ca; alkalosis lowers it — which is why hyperventilation can cause tetany).
NCLEX Pearls
- ✦PTH and vitamin D raise calcium; calcitonin lowers it.
- ✦Calcium and phosphate are inversely related — high PTH raises Ca and lowers phosphate.
- ✦Total calcium is affected by albumin; low albumin → falsely low total Ca (active ionized may be normal).
- ✦Correction: +0.8 mg/dL Ca per 1 g/dL albumin below 4; or just order an ionized calcium.
- ✦Alkalosis lowers ionized calcium (hyperventilation → tetany); acidosis raises it.
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 →