Description
Description
The Calcium/Creatinine Ratio (24-Hour Urine) is a diagnostic test used primarily to evaluate kidney function and calcium metabolism.
- Calcium is a mineral vital for bone health and muscle function. The kidneys filter it from the blood, reabsorbing most of it and excreting the rest in urine.
- Creatinine is a waste product from normal muscle wear and tear. It is excreted at a relatively constant rate, making it a useful marker to ensure the 24-hour urine collection is complete and to normalize the calcium measurement against the patient’s muscle mass.
Purpose & Clinical Significance
This test is most commonly ordered to:
- Investigate Kidney Stones: High levels of calcium in the urine (hypercalciuria) are a leading cause of calcium-based kidney stones.
- Evaluate Parathyroid Disorders: It helps distinguish between primary hyperparathyroidism (high calcium in blood and urine) and conditions like Familial Hypocalciuric Hypercalcemia (high calcium in blood, but low in urine).
- Assess Bone Health: It can help diagnose causes of osteoporosis or bone loss by determining if the body is losing excessive calcium through urine.
Procedure
The test requires a strictly timed 24-hour urine collection:
- Day 1 Morning: Empty your bladder into the toilet (do not collect this first void) and record the time.
- Collection Period: Collect all urine for the next 24 hours in the provided container. The container is often kept refrigerated or on ice.
- Day 2 Morning: At the exact same time you started on Day 1, empty your bladder one last time and add this to the container.
- The lab measures the total volume, total calcium, and total creatinine to calculate the ratio.
Typical Reference Ranges
- Urine Calcium (24h): Typically 100–300 mg/day (varies by diet and lab).
- Ca/Cr Ratio: While specific ranges vary, a ratio helps adjust for body size. In some contexts (like ruling out FHH), a calcium/creatinine clearance ratio is calculated. A general urine calcium (mg/dL) to urine creatinine (mg/dL) ratio of < 0.14 (or < 0.20 depending on guidelines) is often considered normal in adults, though 24-hour total values are the gold standard.
