CALCIUM LEVEL, 24 HR URINE

LAB1128

11313

CPT code 81050 may be added at an additional charge for volume measurement

10 mL aliquot of a well-mixed, 24-hour collection

2 mL

Unpreserved urine • Urinalysis transport tube (yellow-top, blue fill line, preservative tube)

Refrigerate during and after collection. Collect urine with 25 mL of 6N HCl to maintain a pH <2. Do not include first morning specimen; collect all subsequent voidings. The last specimen collected should be the first morning specimen voided the following morning at the same time as the previous morning's first voiding.
Specify 24-hour total volume and collection duration on specimen container and test requisition.

Plastic urine container

Room temperature

Room temperature: 5 days
Refrigerated: 35 days
Frozen: 6 months

a.m. Mon-Sat

3 days

Oral contraceptive use may depress results.

Calcium, 24-Hour Urine

Male	55-300 mg/24 h
Female	35-250 mg/24 h
Low Calcium Diet
Male	55-200 mg/24 h
Female	35-200 mg/24 h

This quantitative test, performed with a 24-hour urine specimen, may help screen for hypercalciuria, one of the established risk factors for kidney stone formation [1-3]. This test may also help assess metabolic disorders of calcium metabolism, such as hyperparathyroidism, bone disease, and idiopathic hypercalciuria. In general, 24-hour urine specimens are preferred to random urine specimens when measuring calcium for diagnostic evaluation of hypercalciuria [1].

Calcium is essential for bone formation and nerve, muscle, and heart functions. Calcium metabolism is jointly regulated by parathyroid hormone and vitamin D metabolites. Urinary calcium excretion is the major route of calcium elimination and reflects kidney tubular filtration and reabsorption of calcium in addition to dietary intake, intestinal absorption, and bone resorption [2].

Urinary calcium levels may be elevated in patients with idiopathic hypercalciuria, chronic kidney disease, hyperparathyroidism, vitamin D intoxication, Paget disease of bone, sarcoidosis, or conditions that infiltrate and destroy bones (eg, multiple myeloma and a variety of metastatic cancers) [2,3]. Urinary calcium levels may be decreased in patients with hypoparathyroidism, vitamin D deficiency rickets, osteomalacia, or familial hypocalciuric hypercalcemia [2,3].

Note that use of calcium supplements and loop diuretics may cause increased urinary calcium levels; thiazide diuretics may cause decreased urinary calcium levels [3].

This test is also available with creatinine (Calcium, 24-Hour Urine with Creatinine). Because daily urine excretion of creatinine generally shows minimal fluctuation, creatinine excretion is useful in determining whether 24-hour urine specimens for calcium have been completely and accurately collected [2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Williams JC Jr, et al. Urolithiasis. 2021;49(1):1-16.
2. Rifai N, et al. eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elservier Inc; 2022
3. MedlinePlus [Internet]. Calcium-urine. Accessed September 1, 2022. https://medlineplus.gov/ency/article/003603.htm