Urinary Calcium

Urinary calcium refers to the amount of calcium excreted in the urine. It is an important marker for bone metabolism, kidney function, and electrolyte balance.

Normal Range:

• Random urine sample: < 4 mg/kg/day
• 24-hour urine collection: 100–300 mg/day (varies based on diet, age, and renal function)
• Urine calcium/creatinine ratio (spot test):
  • Children: < 0.21
  • Adults: < 0.14

Causes of Increased Urinary Calcium (Hypercalciuria)

(Urinary calcium > 300 mg/day in men, > 250 mg/day in women, or > 4 mg/kg/day in children)

1. Hyperparathyroidism – Increased parathyroid hormone (PTH) leads to calcium mobilization from bones.
2. Excessive dietary calcium or vitamin D intake – Increased absorption leads to higher excretion.
3. Renal leak of calcium (Idiopathic hypercalciuria) – Common cause of kidney stones.
4. Bone disorders (e.g., osteoporosis, Paget’s disease) – Increased bone resorption releases calcium.
5. Loop diuretics (e.g., furosemide) – Increase calcium excretion.
6. Sarcoidosis or granulomatous diseases – Increased vitamin D activation leads to hypercalciuria.
7. Cushing’s syndrome – Increased cortisol levels affect bone resorption.

Causes of Decreased Urinary Calcium (Hypocalciuria)

(Urinary calcium < 100 mg/day)

1. Hypoparathyroidism – Low PTH reduces calcium release from bones.
2. Vitamin D deficiency – Leads to decreased calcium absorption.
3. Chronic kidney disease (CKD) – Impaired filtration and calcium handling.
4. Thiazide diuretics – Reduce calcium excretion.
5. Malabsorption syndromes (e.g., celiac disease, Crohn’s disease) – Decreased calcium absorption.

Clinical Significance:

• Kidney Stones (Nephrolithiasis): High urinary calcium is a major risk factor for calcium oxalate and calcium phosphate stones.
• Osteoporosis Evaluation: High urinary calcium may indicate excessive bone loss.
• Metabolic Disorders: Helps in diagnosing parathyroid and vitamin D-related conditions.

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