Calcium, 24-Hour Urine
The 24-hour urine calcium test measures total daily renal calcium excretion, integrating diurnal variation and dietary intake. It is the reference investigation for hypercalciuria in stone-formers, distinguishes primary hyperparathyroidism from familial hypocalciuric hypercalcaemia, and monitors vitamin D therapy.
1
Biomarkers
Urine (24-hour)
Sample
3–5 business days
Turnaround
No
Fasting
What is the 24-Hour Urine Calcium test?
The 24-Hour Urine Calcium test quantifies total daily renal calcium excretion and is the cornerstone investigation of recurrent nephrolithiasis and disorders of calcium homeostasis. Unlike a spot urine calcium-to-creatinine ratio, the timed collection accounts for diurnal and meal-related variation, providing a reproducible measure that informs both diagnosis and management. Practitioners order this test to phenotype stone-formers and tailor prevention strategies, to investigate unexplained hypercalcaemia or hypocalcaemia, and to monitor the renal effects of vitamin D therapy or immobilisation. It is interpreted alongside serum calcium, parathyroid hormone, vitamin D, and often a complete 24-hour stone-risk panel that includes oxalate, citrate, uric acid, volume, and pH. Because urinary calcium is diet-sensitive, the result must be read in the context of sodium and protein intake; some protocols specify a controlled diet before or during collection.
What does the 24-Hour Urine Calcium test measure?
Urinary calcium excretion reflects the net balance of filtered load, renal tubular reabsorption, and dietary intake. The kidney filters roughly 10 g of calcium daily at the glomerulus; more than 98% is reabsorbed along the nephron, predominantly in the proximal tubule and thick ascending limb. Parathyroid hormone suppresses distal calcium excretion, while vitamin D increases intestinal absorption and filtered load. The 24-hour collection integrates diurnal variation and provides a time-averaged measure of renal calcium handling, making it the reference standard for assessing calciuria in the evaluation of nephrolithiasis and disorders of calcium metabolism.
Elevated 24-hour urinary calcium (hypercalciuria) is the most common metabolic risk factor for calcium-containing kidney stones and may signal primary hyperparathyroidism, excessive vitamin D, renal phosphate leak, or idiopathic hypercalciuria. Low excretion (hypocalciuria) occurs with hypoparathyroidism, vitamin D deficiency, malabsorption, thiazide diuretics, and familial hypocalciuric hypercalcaemia. The test is essential for stone-risk stratification, guiding dietary and pharmacological interventions, and distinguishing renal from non-renal causes of hypercalcaemia.
Why is the 24-Hour Urine Calcium test ordered?
- Evaluation of recurrent calcium oxalate or calcium phosphate nephrolithiasis to identify hypercalciuria and guide dietary or pharmacological stone prevention
- Investigation of hypercalcaemia to distinguish primary hyperparathyroidism from familial hypocalciuric hypercalcaemia, where urinary calcium is characteristically low
- Assessment of patients with osteoporosis or fragility fractures in whom excessive urinary calcium loss may contribute to bone mineral depletion
- Monitoring of high-dose vitamin D or calcium supplementation to detect subclinical hypercalciuria before it becomes symptomatic
- Work-up of hypocalcaemia or suspected hypoparathyroidism, where low urinary calcium supports the diagnosis and guides replacement therapy
- Evaluation of renal tubular disorders such as Dent disease or Bartter syndrome, in which hypercalciuria is a cardinal feature
- Screening of first-degree relatives of patients with idiopathic hypercalciuria, given the heritable tendency
- Assessment of immobilised or bed-bound patients at risk of hypercalciuria and stone formation from increased bone resorption
Sample collection and turnaround
Sample type
Urine (24-hour)
Fasting required
No
Collection method
At-home collection kit
Turnaround
3–5 business days
Collection notes
Patient collects all urine over a complete 24-hour period in the container(s) provided by Access Medical Laboratories. Discard the first morning void at the start time and collect every subsequent void, including the first morning void exactly 24 hours later. Refrigerate the container during collection or add the preservative supplied. Record exact start and stop times. Some protocols recommend a controlled diet (moderate sodium and protein) for 2–3 days before and during collection to improve interpretability; verify with the ordering clinician.
Specimen requirements
Complete 24-hour urine collection with total volume recorded. Acidification (HCl preservative) is often used to prevent calcium precipitation. Aliquot forwarded for calcium and creatinine; the remainder may be stored for concurrent oxalate, citrate, uric acid, and pH if a stone panel is ordered.
What can affect 24-Hour Urine Calcium results?
Sodium and calcium are co-transported in the proximal tubule and loop of Henle, so high dietary sodium increases calcium excretion proportionately; every 100 mmol of sodium raises urinary calcium by roughly 25–40 mg.
High protein intake increases the renal acid load and obligate calcium excretion to buffer it, and also raises glomerular filtration of calcium; vegetarian diets produce less calciuria than omnivorous diets with equivalent calcium intake.
Thiazides enhance distal tubular calcium reabsorption and are first-line pharmacotherapy for hypercalciuria; the effect persists with chronic use.
The validity of the result depends entirely on complete collection; under-collection underestimates excretion, while inadvertent inclusion of an extra void inflates it. Measuring 24-hour creatinine excretion helps assess completeness.
Loop diuretics inhibit the Na-K-2Cl cotransporter in the thick ascending limb, abolishing the lumen-positive voltage that drives paracellular calcium reabsorption, and produce marked hypercalciuria.
Both increase bone resorption and filtered calcium load; immobilisation is a well-recognised cause of hypercalciuria and stone risk in spinal-cord injury and prolonged bed rest.
What do 24-Hour Urine Calcium results mean?
Elevated
Hypercalciuria (typically >300 mg/24 h in men, >250 mg/24 h in women, though definitions vary) suggests primary hyperparathyroidism, excessive vitamin D, sarcoidosis or granulomatous disease, renal phosphate wasting, distal renal tubular acidosis, idiopathic hypercalciuria, high dietary sodium or protein, loop diuretics, glucocorticoids, immobilisation, or bone metastases. In stone-formers it is the dominant modifiable risk factor and warrants dietary sodium restriction, adequate hydration, and consideration of thiazide therapy.
Normal
Normal 24-hour urinary calcium in the context of recurrent stones suggests that other metabolic factors — low urine volume, hyperoxaluria, hypocitraturia, hyperuricosuria, or persistently alkaline pH — are driving stone risk. A complete 24-hour stone panel is often warranted.
Reduced
Hypocalciuria (<100 mg/24 h) occurs with hypoparathyroidism, vitamin D deficiency, malabsorption (coeliac disease, inflammatory bowel disease), chronic kidney disease with reduced filtered load, thiazide diuretics, and familial hypocalciuric hypercalcaemia. The calcium-to-creatinine clearance ratio helps separate familial hypocalciuric hypercalcaemia (ratio typically <0.01) from primary hyperparathyroidism (ratio >0.02).
Note: Urinary calcium is highly diet-dependent, so the result must be interpreted with concurrent sodium (target <100 mmol/24 h), protein, and calcium intake. A single collection may not reflect habitual excretion; repeat testing on a controlled diet improves precision. Always check 24-hour creatinine to verify collection completeness (expected roughly 15–20 mg/kg in women, 20–25 mg/kg in men). Serum calcium, PTH, and vitamin D are essential companion tests.
Frequently asked questions
Urinary calcium excretion varies throughout the day with meals and activity. A 24-hour collection integrates these fluctuations and provides a reproducible, time-averaged measure that is the reference standard for assessing hypercalciuria and stone risk.
How to access the 24-Hour Urine Calcium test
The 24-Hour Urine Calcium reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Pearle MS, et al. Medical management of kidney stones: AUA guideline. J Urol. (2014)
- KDIGO 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease–Mineral and Bone Disorder (CKD-MBD). Kidney Int Suppl. (2017)
- Bushinsky DA, et al. Nephrolithiasis. In: Brenner & Rector's The Kidney, 11th ed. (2020)
- Worcester EM, Coe FL. Clinical practice: calcium kidney stones. N Engl J Med. (2010)
- Arrabal-Polo MA, et al. Mineral density and bone remodelling markers in patients with calcium lithiasis. BJU Int. (2013)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.