Calcium, 24-Hour Urine (w/ Creatinine) (1635X)

Test Code

3244N

CPT Codes
82340, 82570

Includes

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

Preferred Specimen

10 mL 24-hour urine collected in a urinalysis transport tube (yellow-top, blue fill lin1, preservative)

Minimum Volume

2 mL

Other Acceptable Specimens

10 mL conc. glacial acetic acid • 10 g boric acid • Urinalysis transport tube (yellow-top, blue fill line, preservative tube)

Instructions

Please submit a 10 mL aliquot of a 24-hour collection. Collect urine with 25 mL of 6N HCl to maintain a pH below 3. It is acceptable to add preservative after collection if urine was refrigerated during collection. Refrigerate during and after collection. Do not include first morning specimen; collect all subsequent voidings. The last sample collected should be the first morning specimen voided the following morning at the same time as the previous mornings first voiding. Record 24-hour urine volume on test request form and urine vial.

Transport Temperature

Room temperature

Specimen Stability

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

Methodology
Spectrophotometry (SP)

Setup Schedule

5 days a week

Limitations

Oral contraceptive use may depress results.

Clinical Significance

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]. Creatinine excretion is useful in determining whether 24-hour urine specimens for calcium have been completely and accurately collected because daily urine excretion of creatinine generally shows minimal fluctuation [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].

A calcium/creatinine clearance ratio, calculated from 24-hour urinary calcium and creatinine concentrations and total serum calcium and creatinine concentrations may help differentiate primary hyperparathyroidism (PHPT) from familial hypocalciuric hypercalcemia (FHH) [4].

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

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
4. Arshad MF, et al. Postgrad Med J. 2021;97(1151):577-582.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.