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HelpTest Code CALU Calcium, 24 Hour, Urine
Useful For
Evaluation of calcium oxalate and calcium phosphate kidney stone risk, and calculation of urinary supersaturation
Evaluation of bone diseases, including osteoporosis and osteomalacia
Special Instructions
Method Name
Photometric
Reporting Name
Calcium, 24 HR, USpecimen Type
UrineNecessary Information
24-Hour volume (in milliliters) is required.
Specimen Required
Patient Preparation: Patient cannot have a laxative during the 24-hour collection period.
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube: 24-hour graduated urine container with no metal cap or glued insert
Submission Container/Tube: Plastic, 5 mL tube or a clean, plastic aliquot container with no metal cap or glued insert
Specimen Volume: 4 mL
Collection Instructions:
1. Collect urine for 24 hours.
2. Refrigerate specimen within 4 hours of completion of 24-hour collection.
Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Refrigerated (preferred) | 14 days | |
| Frozen | 30 days | ||
| Ambient | 72 hours |
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitabilityClinical Information
Calcium is the fifth most common element in the body. It is a fundamental element necessary to form electrical gradients across membranes, an essential cofactor for many enzymes, and the main constituent in bone. Under normal physiologic conditions, the concentration of calcium in serum and in cells is tightly controlled. Calcium is excreted in both urine and feces. Ordinarily about 20% to 25% of dietary calcium is absorbed and 98% of filtered calcium is reabsorbed in the kidney. Traffic of calcium between the gastrointestinal tract, bone, and kidney is tightly controlled by a complex regulatory system that includes vitamin D and parathyroid hormone. Sufficient bioavailable calcium is essential for bone health. Excessive excretion of calcium in the urine is a common contributor to kidney stone risk.
Reference Values
Males: <250 mg/24 hours*
Females: <200 mg/24 hours*
*Values represent clinical cutoffs above which studies have demonstrated increased risk of kidney stone formation. These values were not determined in a reference range study.
Reference values have not been established for patients who are younger than 18 years of age.
Reference values apply to 24-hour collection.
Interpretation
Increased urinary calcium excretion (hypercalciuria) is a known contributor to kidney stone disease and osteoporosis. Many cases are genetic (often termed idiopathic). Previously such patients were often divided into fasting versus absorptive hypercalciuria depending on the level of urine calcium in a fasting versus fed state, but the clinical utility of this approach is now in question. Overall, the risk of stone disease appears increased when 24-hour urine calcium is above 250 mg in men and above 200 mg in women. Thiazide diuretics are often used to reduce urinary calcium excretion, and repeat urine collections can be performed to monitor the effectiveness of therapy.
Known secondary causes of hypercalciuria include hyperparathyroidism, Paget disease, prolonged immobilization, vitamin D intoxication, and diseases that destroy bone (such as metastatic cancer or multiple myeloma).
Urine calcium excretion can be used to gauge the adequacy of calcium and vitamin D supplementation, for example in states of gastrointestinal fat malabsorption that are associated with decreased bone mineralization (osteomalacia).
Cautions
No significant cautionary statements
Method Description
Calcium ions react with 5-nitro-5'-methyl-BAPTA (NM-BAPTA) under alkaline conditions to form a complex. This complex reacts in the second step with EDTA. The change in absorbance is directly proportional to the calcium concentration and is measured photometrically.(Package insert: Roche CA2 kit. Roche Diagnostics; V5.0 03/2019)
Specimen Retention Time
7 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
82340
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| CALU | Calcium, 24 HR, U | 6874-2 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| CA24 | Calcium, 24 HR, U | 6874-2 |
| TM114 | Collection Duration | 13362-9 |
| VL110 | Urine Volume | 3167-4 |
Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.
Day(s) Performed
Monday through Sunday