AKT · Renal & urology/Fluid, electrolyte & acid-baselow yield

Calcium disorders

Hypercalcaemia (PTH/malignancy) / hypocalcaemia (low PTH/vitamin D/CKD) — corrected for albumin

Overview

Disorders of plasma calcium (interpret CORRECTED for albumin). Hypercalcaemia is, in over 90%, primary hyperparathyroidism (community) or malignancy (hospital) — 'bones, stones, abdominal groans, psychic moans'. Hypocalcaemia (hypoparathyroidism, vitamin D deficiency, CKD, pancreatitis) causes neuromuscular irritability (Chvostek/Trousseau). Detailed endocrine causes are on the endocrine page; this card is the renal/acute angle.

Recognise

Hypercalcaemia: 'bones, stones (renal calculi), abdominal groans (constipation, pancreatitis, ulcers), psychic moans (confusion, depression)', polyuria/thirst, short QT
Hypocalcaemia: perioral/digital paraesthesiae, cramps/tetany, CHVOSTEK (facial tap) and TROUSSEAU (cuff-induced carpopedal spasm) signs, long QT, seizures
Causes — hyperCa: primary hyperparathyroidism (PTH high/normal), malignancy (PTHrP/bone mets/myeloma, PTH low); hypoCa: hypoparathyroidism, vitamin D deficiency, CKD, pancreatitis, hypomagnesaemia

Red flags

Severe hypercalcaemia (≥3.5 / symptomatic) → IV fluids + treat the cause; hypercalcaemia of malignancy → IV fluids then bisphosphonate
Severe symptomatic hypocalcaemia (tetany, seizures, long QT) → IV calcium gluconate

Differentials & how to tell them apart

Primary hyperparathyroidismraised calcium with high/inappropriately-normal PTH — cross-ref endocrine

Hypercalcaemia of malignancyraised calcium with SUPPRESSED PTH (PTHrP/bone mets/myeloma) — find the cancer

Vitamin D deficiency / CKD-MBDhypocalcaemia with low vitamin D / high phosphate + raised PTH (secondary)

Investigations

Corrected calcium, PTH (the key discriminator — high/inappropriately-normal = hyperparathyroidism; suppressed = malignancy/other), phosphate, vitamin D, U&Es (CKD), magnesium, ALP; malignancy screen (myeloma, bone mets) if PTH suppressed; ECG (QT).

Management

HyperCa → IV saline then bisphosphonate; hypoCa → calcium (IV if severe) + vitamin D (+ magnesium)

1Interpret corrected calcium with PTH — the key fork. Symptomatic/severe hypercalcaemia → IV saline rehydration first, then a bisphosphonate; severe symptomatic hypocalcaemia → IV calcium gluconate.Gate: Hypercalcaemia: PTH high/normal = primary hyperparathyroidism; PTH suppressed = malignancy (find the cancer). Hypocalcaemia won't correct if magnesium is low — replace it.
2Treat the cause: parathyroidectomy/cancer therapy/vitamin D repletion/CKD-MBD management. Full endocrine work-up of hyper/hypoparathyroidism is on the endocrine page.

Hypercalcaemia: IV 0.9% saline rehydration first, then IV bisphosphonate — fluids are first-line; bisphosphonate for malignancy; treat the cause (parathyroidectomy, cancer therapy)

Hypocalcaemia: calcium (oral, or IV calcium gluconate if severe/symptomatic) + vitamin D — correct magnesium if low (otherwise calcium won't correct); active vitamin D (alfacalcidol) in CKD/hypoPTH

Treat the underlying cause — parathyroid surgery, cancer treatment, vitamin D repletion, CKD-MBD management

Cinacalcet / specialist therapy — selected hyperparathyroidism/refractory hypercalcaemia

Key points

Interpret calcium CORRECTED for albumin, with PTH. HyperCa: 'bones, stones, groans, moans', short QT → saline then bisphosphonate; PTH high = hyperparathyroidism, PTH low = malignancy. HypoCa: Chvostek/Trousseau, long QT → calcium + vitamin D, and replace magnesium (or it won't correct).

Monitor & prognosis

Calcium/PTH/phosphate/magnesium, renal function, ECG (QT); response to treatment.

Good with cause-directed treatment; hypercalcaemia of malignancy signals advanced disease.

Source: NICE CKS; cross-ref endocrine (parathyroid/bone profile)