How are the optimal levels of urinary calcium determined?

Updated: Jun 02, 2021
  • Author: Stephen W Leslie, MD, FACS; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Optimal levels of urinary calcium have not been determined. Several experts, including the author of this article and Dr. Gary Curhan of Harvard University, have suggested that the current definitions of hypercalciuria and several other 24-hour urinary chemistries are inadequate and may not be reliable when applied to nephrolithiasis. Available definitions are limited by the occasional inclusion in research investigations of recurrent stone formers in the healthy group of study subjects and by poorly defined controls. [7] In addition, the parameters and ranges are not optimized from the point of view of kidney stone disease or production.

The data from several large databases (including the Nurses' Health Study and the Health Professional Follow-up Study) indicate that, with the current definition of hypercalciuria, a substantial proportion of controls would be defined as abnormal. The relative risk of stone production appears to be continuous, along a sliding scale, rather than dichotomous with a single arbitrary level that differentiates healthy people from those who form stones.

Therefore, although the gross total 24-hour urinary calcium excretion remains useful, the urinary calcium concentration is probably a more reliable dynamic indicator of stone formation risk. [7] Further study is needed to confirm these conclusions and to possibly establish better 24-hour urine reference ranges for calcium and other metabolic stone–risk chemistries. (See Workup.)

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