Urine Calcium: Laboratory Measurement and Clinical Utility

Kevin F. Foley, PhD, DABCC; Lorenzo Boccuzzi, DO

Disclosures

Lab Med. 2010;41(11):683-686. 

In This Article

Hypercalciuria

Any disease causing increases in serum calcium can lead to increases in urine calcium. In addition to hyperparathyroidism, other diseases include multiple myeloma (or any osteolytic neoplasm), osteoporosis, vitamin D overdose, renal tubular acidosis, hyperthyroidism, Paget's disease, and sarcoidosis. Drugs containing calcium (such as some antacids) and calcium supplements can lead to direct increases in urine calcium. The diuretic spironolactone can also cause increases in urine calcium since it is given as a calcium salt and appears to decrease tubule reabsorption of calcium. Androgens such as nandrolone and treatment with growth hormone can also cause increases in urine calcium. Acetazolamide and systemic corticosteroids are also associated with increased CE.

Patients who have alterations in serum calcium levels are often asymptomatic at the time their abnormal calcium levels are discovered by the clinical laboratory. However, patients with abnormal calcium levels can present with severe signs and symptoms, such as tetany and seizure. Other clinical symptoms suggestive of alteration in calcium metabolism may include perioral and peripheral paresthesias, carpal and pedal spasms, muscle aches, depression, anxiety, fatigue, constipation, abdominal pain, polyuria, and polydypsia. Irritability and lethargy may be the only presenting symptoms in an infant. Maternal hypercalcemia can result in an increased risk of spontaneous abortions, fetal demise, and neonatal hypocalcemia. Maternal hypocalcemia can cause neonatal hyperparathyroidism with abnormal serum calcium levels and osteitis fibrosa cystica.[6] Unrecognized hypoparathyroidism and FHH in women who were diagnosed after the birth of their infants have been reported as well.[6]

Although not ordered on a frequent basis by primary care clinicians, urinary calcium determination may have a significant impact on the diagnosis and treatment of some diseases. In the initial investigation of identifying the cause of abnormal calcium metabolism, a 24-hour urine collection for calcium, urine volume, and creatinine should be performed along with blood testing. The 2 methods most commonly used by clinicians to determine abnormality in renal excretion of calcium are measurement of 24-hour urine CE or calculation of the 24-hour urine calcium/creatinine excretion ratio (CR).[7] Recent research, however, seems to indicate that these tests may not adequately identify hyperparathyroid patients. Instead, the calculation of the calcium/creatinine clearance ratio (CCCR), also known as the fractional excretion of calcium (FEca), may be a better method by which to identify the cause of abnormal calcium determinations of plasma calcium and creatinine along with the 24-hour renal excretions of calcium and creatinine and applying the following formula: (24-hour U-calcium/P-total calcium)/(24-hour U-creatinine/P-creatinine).[8,9]

A fasting urine calcium may also be useful in uncovering calcium overdose (increased absorption from the gut). If a 2-hour urine collection is obtained after a 14-hour fast, the urine calcium:creatinine ratio should fall to <0.15. If it is >0.15, metabolic/nephrogenic hypercalciuria is suspected.[10]

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