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

Use in Assessing Stones

In general, patients with calcium urolithiasis excrete more lithogenic substances (calcium and oxalate) in urine than non-stone formers. They also typically secrete less of the stone-inhibitory substances citrate and magnesium. Yet measurement of urine calcium is not considered a good predictive measurement for stone formation. Calcium-based risk markers for urolithiasis have been studied and include ratios such as the calcium/magnesium ratio, the calcium/citrate ratio, and the (calcium * oxalate)/(magnesium * citrate) ratio.[22] Since stone formation is multi-factorial and inherently variable, currently neither calcium nor any other marker for urolithiasis risk is well accepted.

Although urine calcium is not a decisive marker for stone formation, urine calcium measurement may play a role in identifying certain patients who form kidney stones due to the presence of systemic disease (particularly PH). Parks and colleagues compared laboratory features and outcomes of treatment in urinary stone-forming patients with hyperparathyroidism to those without systemic disease.[23] The authors concluded that the hypercalciuria in PH patients who formed stones was greater than the hypercalciuria of the stone-formers without systemic disease. Thus, measurement of the CCCR might help discriminate stone-formers with PH from those with other disorders. This information would be useful in determining appropriate treatment intervention. Interestingly, surgical treatment of the PH did not completely resolve the hypercalciuria or hypophosphatemia in these patients, suggesting the presence of another underlying disorder. This demonstrates the complex nature of calcium homeostasis in that PTH is only 1 of the players involved.

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