What is resorptive hypercalciuria?

Updated: Apr 23, 2019
  • Author: Stephen W Leslie, MD, FACS; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Resorptive hypercalciuria is almost always due to hyperparathyroidism. This generally accounts for 3-5% of all cases of hypercalciuria, although some reports have indicated an incidence as high as 8%. Increased PTH levels cause a release of calcium from bone stores.

In addition, resorptive hypercalciuria increases calcium absorption from the digestive tract by raising vitamin D-3 levels and decreases renal excretion of calcium by stimulating calcium reabsorption in the distal renal tubule. Eventually, the hypercalcemia overcomes this renal calcium–conserving quality and results in an increased net loss of calcium through the urine (hypercalciuria).

Hyperparathyroidism does not always result in calcium-stone disease. The reason for this is unclear but may reflect urinary volume and optimal levels of other urinary metabolites, such as oxalate, uric acid, sodium, phosphate, citrate, urinary volume, and serum vitamin D-3. In some cases, the vitamin D-3 level has been suggested to be responsible for determining which patients with hyperparathyroidism actually develop kidney stones. This apparently reasonable hypothesis remains unproved, however, and the current evidence suggests that vitamin-D levels cannot be the only reason that some patients with hyperparathyroidism do not develop stones.

Hyperparathyroidism produces a lower urinary calcium excretion for the patient’s serum calcium level than does hypercalcemia from other causes. In other words, for any level of serum calcium, patients with hyperparathyroidism have lower urinary calcium excretion than do patients with hypercalcemia who have normal PTH levels. This is due to the calcium-conserving effect of PTH on the kidneys.

Diagnosis and treatment

Hyperparathyroidism should be suspected in calcium stone–forming patients with significant hypercalciuria, even in those with only mild hypercalcemia. Failure to identify a curable cause of osteoporosis and calcium nephrolithiasis can be easily avoided just by checking the parathyroid hormone level routinely in hypercalciuric patients with relatively high serum calcium levels. [10]

Patients with hyperparathyroidism who have parathyroid surgery and subsequently demonstrate normal urinary calcium levels are still at risk for developing stones at about the same rate as other calcium-stone formers. Therefore, retesting with 24-hour urine determinations is recommended for calcium-stone formers even after successful parathyroid surgery has normalized their serum calcium levels. Urinary cyclic adenosine monophosphate (cAMP) can be used as a substitute for serum PTH level determinations to monitor patients who have already been diagnosed.


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