Table of Contents
Overview – Calcium & Phosphate Disorders
Disorders of calcium and phosphate regulation are common endocrine and metabolic problems encountered in both acute and chronic settings. These imbalances often involve the interplay between parathyroid hormone (PTH), vitamin D, renal function, and bone metabolism. Conditions such as hyperparathyroidism, rickets, and osteoporosis can result in life-altering symptoms including tetany, fractures, and renal complications.
Hypercalcaemia
Causes
- Primary hyperparathyroidism
- Malignancy (e.g. breast cancer, multiple myeloma)
- Vitamin D toxicity
- Secondary renal hyperparathyroidism
Pathophysiology
- ↑ PTH → ↑ Bone resorption, ↑ GI calcium absorption, ↓ renal calcium excretion
- Hypercalcaemia often coexists with hypophosphataemia (due to ↑ phosphate excretion)
Hypocalcaemia
Causes
- Vitamin D deficiency or impaired activation
- Lack of sunlight
- Dietary deficiency
- Chronic kidney disease
- Hypoparathyroidism (acquired or congenital)
- Leads to ↓ PTH → ↓ calcium reabsorption and ↓ vitamin D activation
Rickets
Definition
- A paediatric disorder of impaired bone mineralisation due to vitamin D deficiency
Pathophysiology
- ↓ Vitamin D → ↓ calcium & phosphate absorption
- Bone stores initially buffer plasma levels
- Eventually:
- ↑↑ PTH secretion
- ↑ Bone resorption → ↑ plasma calcium, ↓ plasma phosphate
- Late-stage: Plasma calcium falls → tetany risk
Treatment
- Oral calcium supplements
- Exogenous vitamin D
Hypoparathyroidism
Definition
- Inadequate secretion of PTH from parathyroid glands
Effects
- ↓ Bone calcium mobilisation → hypocalcaemia
- Severe hypocalcaemia → neuromuscular irritability, tetany
- May involve the larynx → respiratory compromise
Hyperparathyroidism
Definition
- Excess secretion of PTH, usually from a parathyroid adenoma
Effects
- ↑ Osteoclastic bone resorption
- Hypercalcaemia
- Hypophosphataemia due to renal phosphate wasting
Osteoporosis
Definition
- Reduction in total bone mass with normal mineralisation
- Not primarily a calcium or phosphate disorder
Aetiology
- ↓ Osteoblastic activity
- ↑ Osteoclastic activity
- Risk factors:
- Sedentary lifestyle
- Malnutrition
- Postmenopausal oestrogen deficiency
- Cushing’s syndrome (↑ cortisol → ↓ bone matrix protein synthesis)
Summary – Calcium & Phosphate Disorders
Disorders of calcium and phosphate regulation are primarily driven by imbalances in PTH, vitamin D, and renal function. Conditions like hyperparathyroidism and rickets can lead to serious clinical consequences, including bone deformities, tetany, and chronic skeletal degeneration. Management hinges on identifying the underlying cause and correcting the biochemical imbalance. For broader endocrinology content, see our Endocrine Overview.