Disorders of calcium and phosphate balance
Calcium and phosphate are essential minerals involved in skeletal integrity, neuromuscular function, intracellular signaling, blood coagulation, and energy metabolism. Their homeostasis is tightly regulated by the coordinated actions of the parathyroid hormone (PTH), vitamin D, and calcitonin, acting primarily on the bone, kidneys, and gastrointestinal tract. Disorders arise when these regulatory mechanisms are disrupted.
Normal Calcium and Phosphate Homeostasis[edit | edit source]
Calcium[edit | edit source]
- Normal serum total calcium: 8.5–10.5 mg/dL
- Ionized (biologically active) calcium: ~50%
- Bound to proteins (mainly albumin): ~40%
- Complexed with anions: ~10%
Phosphate[edit | edit source]
- Normal serum phosphate: 2.5–4.5 mg/dL
- Major intracellular anion
- Essential for bone mineralization, ATP production, and cellular signaling
Regulatory Hormones[edit | edit source]
- Parathyroid hormone (PTH): Increases serum calcium, decreases serum phosphate
- Vitamin D (Calcitriol): Increases intestinal absorption of calcium and phosphate
- Calcitonin: Lowers serum calcium by inhibiting bone resorption (minor role in adults)
Disorders of Calcium Balance[edit | edit source]
Hypocalcemia[edit | edit source]
Serum calcium level below the normal reference range.
Etiology:
- Hypoparathyroidism (surgical, autoimmune)
- Vitamin D deficiency or resistance
- Chronic kidney disease
- Acute pancreatitis
- Massive blood transfusion (citrate binding)
- Hypomagnesemia
Pathophysiology:
Low calcium increases neuronal membrane excitability, leading to neuromuscular irritability.
Clinical Features:
- Perioral numbness and tingling
- Muscle cramps and tetany
- Carpopedal spasm
- Seizures
- Cardiac arrhythmias
- Positive Chvostek sign and Trousseau sign
Laboratory Findings:
- ↓ Serum calcium
- ↑ Serum phosphate (in hypoparathyroidism)
- ↓ PTH (in primary hypoparathyroidism)
Hypercalcemia[edit | edit source]
Serum calcium level above the normal reference range.
Etiology:
- Primary hyperparathyroidism
- Malignancy (PTHrP-secreting tumors, bone metastases)
- Vitamin D intoxication
- Sarcoidosis and other granulomatous diseases
- Prolonged immobilization
- Thiazide diuretics
Pathophysiology:
Elevated calcium reduces neuromuscular excitability and impairs renal concentrating ability.
Clinical Features:
Classically described as:
- Bones: Bone pain, fractures
- Stones: Renal calculi
- Groans: Abdominal pain, constipation
- Psychiatric overtones: Confusion, depression
- Polyuria and polydipsia
- Cardiac arrhythmias
Laboratory Findings:
- ↑ Serum calcium
- ↓ Serum phosphate (in hyperparathyroidism)
- ↑ PTH or PTHrP (depending on cause)
Disorders of Phosphate Balance[edit | edit source]
Hypophosphatemia[edit | edit source]
Serum phosphate level below the normal range.
Etiology:
- Malnutrition or refeeding syndrome
- Vitamin D deficiency
- Hyperparathyroidism
- Chronic alcoholism
- Renal tubular defects
- Antacid abuse
Pathophysiology:
Low phosphate impairs ATP generation, leading to cellular dysfunction.
Clinical Features:
- Muscle weakness
- Rhabdomyolysis
- Hemolysis
- Impaired myocardial contractility
- Neurological symptoms (confusion, seizures)
- Bone pain and osteomalacia (chronic cases)
Hyperphosphatemia[edit | edit source]
Serum phosphate level above the normal range.
Etiology:
- Chronic kidney disease
- Hypoparathyroidism
- Tumor lysis syndrome
- Rhabdomyolysis
- Excess phosphate intake
Pathophysiology:
Elevated phosphate binds calcium, leading to secondary hypocalcemia and soft-tissue calcification.
Clinical Features:
- Often asymptomatic initially
- Signs of hypocalcemia (tetany, paresthesia)
- Vascular and soft tissue calcification (chronic)[1]
Disorders Affecting Both Calcium and Phosphate[edit | edit source]
Hypoparathyroidism[edit | edit source]
- ↓ PTH
- ↓ Calcium
- ↑ Phosphate
- Causes: thyroid/parathyroid surgery, autoimmune destruction
Hyperparathyroidism[edit | edit source]
- ↑ PTH
- ↑ Calcium
- ↓ Phosphate
- Causes: parathyroid adenoma, hyperplasia
Vitamin D Deficiency[edit | edit source]
- ↓ Calcium
- ↓ Phosphate
- Leads to rickets in children and osteomalacia in adults
Chronic Kidney Disease–Mineral and Bone Disorder (CKD-MBD)[edit | edit source]
- ↓ Phosphate excretion → hyperphosphatemia
- ↓ Calcitriol synthesis
- Secondary hyperparathyroidism
- Renal osteodystrophy
- ↑ Kumar V, Abbas AK, Aster JC. Robbins and Cotran Pathologic Basis of Disease. 10th ed. Elsevier; 2021. Hall JE, Guyton AC. Guyton and Hall Textbook of Medical Physiology. 14th ed. Elsevier; 2021.
