From the Guidelines
Urinary calcium levels are primarily ordered to assess calcium excretion in the urine, which helps diagnose and monitor conditions related to calcium metabolism, particularly in patients with kidney stones. This test is crucial for evaluating patients with recurrent kidney stones, as hypercalciuria (excessive urinary calcium) is present in about 50% of stone formers 1. The test can be performed as a 24-hour urine collection, which provides the most accurate measurement of total calcium excretion, or as a spot urine calcium-to-creatinine ratio for screening purposes. Some key points to consider when interpreting urinary calcium levels include:
- Normal 24-hour urinary calcium excretion is typically less than 250 mg/day for men and less than 200 mg/day for women on a regular diet.
- Elevated levels may indicate conditions such as primary hyperparathyroidism, vitamin D toxicity, certain cancers, or excessive calcium intake, while low levels might suggest vitamin D deficiency, malabsorption, or hypoparathyroidism.
- The results should be interpreted in conjunction with serum calcium levels, parathyroid hormone levels, and clinical presentation for a comprehensive assessment of calcium metabolism 1.
- Clinicians should obtain serum intact parathyroid hormone level as part of the screening evaluation if primary hyperparathyroidism is suspected, and stone analysis should be performed at least once when a stone is available 1.
- Metabolic testing, including 24-hour urine collections, can help identify metabolic and environmental risk factors and direct dietary and medical therapy 1. In patients with high or relatively high urine calcium and recurrent calcium stones, thiazide diuretics should be offered, with dosages including hydrochlorothiazide (25 mg orally, twice daily; 50 mg orally, once daily), chlorthalidone (25 mg orally, once daily), and indapamide (2.5 mg orally, once daily) 1.
From the Research
Reasons for Ordering Urinary Calcium Level
- To evaluate patients with suspected primary hyperparathyroidism (PHPT), as elevated urinary calcium levels are a common finding in this condition 2, 3
- To assess the risk of kidney stone formation, as hypercalciuria is a contributing factor to stone formation in the kidneys and urinary tract 2, 4, 5
- To monitor patients with nephrolithiasis, as they may have elevated urinary calcium levels and other urinary disorders such as low urinary volume, high urinary pH, and hypocitraturia 3, 5
- To evaluate the effectiveness of parathyroidectomy in normalizing serum calcium and parathyroid hormone levels, and reducing urinary calcium levels 3
- To assess the risk of mineral and bone disorders in patients with chronic kidney disease (CKD), as CKD can disturb mineral homeostasis leading to elevated parathyroid hormone levels and hypercalciuria 6
Key Findings
- Elevated urinary calcium levels are a common finding in patients with primary hyperparathyroidism and nephrolithiasis 2, 3, 5
- Hypercalciuria is a contributing factor to stone formation in the kidneys and urinary tract 2, 4, 5
- Parathyroidectomy can normalize serum calcium and parathyroid hormone levels, and reduce urinary calcium levels in patients with primary hyperparathyroidism and nephrolithiasis 3
- CKD can disturb mineral homeostasis leading to elevated parathyroid hormone levels and hypercalciuria, and intermittent parathyroid hormone administration may be beneficial in preventing and treating mineral and bone disorders in CKD patients 6