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Test Code CALU Calcium, 24 Hour, Urine

Useful For

Evaluation of calcium oxalate and calcium phosphate kidney stone risk, and calculation of urinary supersaturations

 

Evaluation of bone diseases, including osteoporosis and osteomalacia

Method Name

Photometric, NM-BAPTA Reaction

Reporting Name

Calcium, 24 Hr, U

Specimen Type

Urine


Specimen Required


Collection Container/Tube: 24-hour graduated urine container with no metal cap or glued insert

Submission Container/Tube: Plastic, 5-mL tube (T465) 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:

1. 24-Hour volume is required.

2. See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens in Special Instructions for multiple collections.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Urine Refrigerated (preferred) 14 days
  Frozen  14 days
  Ambient  72 hours

Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

NA

Clinical 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

 

Reference values have not been established for patients <18 years and >83 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 >250 mg in men and >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).

Clinical Reference

1. Curhan GC, Willett WC, Speizer FE, Stampfer MJ: Twenty-four-hour urine chemistries and the risk of kidney stones among women and men. Kidney Int 2001;59:2290-2298

2. Metz MP: Determining urinary calcium/creatinine cut-offs for the pediatric population using published data. Ann Clin Biochem 2006;43:398-401

3. Pak CY, Britton F, Peterson R, et al: Ambulatory evaluation of nephrolithiasis. Classification, clinical presentation and diagnostic criteria. Am J Med 1980;69:19-30

4. Pak CY, Kaplan R, Bone H, et al: A simple test for the diagnosis of absorptive, resorptive and renal hypercalciurias. N Engl J Med 1975;292:497-500

Day(s) and Time(s) Performed

Monday through Sunday; Continuously.

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined 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
CACN Calcium Concentration In Process

Urine Preservative Collection Options

Ambient

Yes

Refrigerated

Preferred

Frozen

Yes

6N HCl

Yes

50% Acetic Acid

Yes

Na2CO3

No

Toluene

Yes

6N HNO3

Yes

Boric Acid

Yes

Thymol

Yes