The 24-hour urinary calcium-to-creatinine ratio is an important test used to assess calcium metabolism and evaluate kidney function. It measures the amount of calcium and creatinine excreted in urine over a 24-hour period and expresses this as a ratio. This test helps identify disorders related to calcium balance, kidney health, and bone metabolism.

Uses of the 24-Hour Urinary Calcium-to-Creatinine Ratio:

1. Assessment of Hypercalciuria:

• Hypercalciuria (excessive urinary calcium excretion): This condition can lead to kidney stones and may be a sign of underlying issues such as hyperparathyroidism, certain types of bone disease, or excess dietary calcium intake.
• Risk evaluation for kidney stones: The test helps determine if a person is excreting too much calcium in their urine, which increases the risk of calcium-based kidney stones.

1. Evaluation of Hypocalciuria:

• Hypocalciuria (low urinary calcium excretion): May suggest conditions like hypoparathyroidism, malabsorption syndromes, or dietary calcium deficiency.

1. Diagnosis of Metabolic Bone Disorders:

• Osteoporosis and osteopenia: This ratio may help assess bone loss and metabolic bone disorders where calcium handling is abnormal.
• Primary hyperparathyroidism: Elevated urinary calcium relative to creatinine is a common finding in primary hyperparathyroidism, aiding in its diagnosis.

1. Monitoring in Pediatric Cases:

• Idiopathic hypercalciuria: The test is useful in children to assess for this condition, which can cause hematuria (blood in the urine), abdominal pain, or frequent urinary tract infections.
• Rickets and other growth disorders: The ratio can help evaluate calcium status in conditions that affect bone development in children.

Procedure Overview:

• 24-hour urine collection: The patient collects all urine produced over 24 hours in a special container provided by the laboratory.
• Measurement and calculation: The laboratory analyzes the urine sample to measure total calcium and creatinine excretion and then calculates the ratio.

Interpretation of Results:

• Normal ranges:
• The specific range varies by age, sex, and laboratory standards.
• In adults, a typical calcium-to-creatinine ratio is generally less than 0.2 mg/mg.
• High calcium-to-creatinine ratio:
• Possible causes: Hyperparathyroidism, excessive dietary calcium or vitamin D intake, Paget’s disease, or certain malignancies that affect bone metabolism.
• Low calcium-to-creatinine ratio:
• Possible causes: Hypoparathyroidism, malabsorption, chronic kidney disease, or inadequate dietary calcium intake.

Significance of Creatinine in the Ratio:

• Creatinine is used as a reference marker for urine concentration. By comparing calcium excretion to creatinine, the test provides a standardized way to assess calcium excretion that accounts for differences in urine volume due to hydration status.

Clinical Context:

• This test is often ordered alongside blood tests that measure serum calcium, phosphorus, parathyroid hormone (PTH), and vitamin D levels to get a comprehensive view of calcium metabolism and bone health.
• Medications, diet, and hydration status can influence the results, so patients may be instructed to follow specific dietary guidelines or maintain consistent fluid intake before and during the test period.