Idiopathic Hypercalciuria
Idiopathic hypercalciuria is identified by the following:
- Persistent hypercalciuria despite normal or restricted calcium intake
- Normal levels of parathyroid hormone (PTH), phosphorus, and 1,25-dihydroxy-vitamin D (calcitriol) in the presence of hypercalciuria
- Normal serum calcium levels
An alias for idiopathic hypercalciuria is fasting hypercalciuria, because increased urinary calcium persists and sometimes worsens while fasting or on a low-calcium diet.
Mineral loss from bone predominates in idiopathic hypercalciuria, but there is also a minor component of intestinal hyperabsorption of calcium and reduced renal calcium reabsorption. Distinguishing among intestinal hyperabsorptive hypercalciuria, renal leak hypercalciuria, and idiopathic or fasting hypercalciuria can be difficult and subtle. It has been argued that differentiating these hypercalciuric subtypes is not useful. Also, it is impractical to collect multiple 24-hour urine samples in the setting of controlled high- vs low-calcium diets.
Patients with idiopathic hypercalciuria have a high incidence of renal stones. Conversely, 40% to 50% of patients with recurrent kidney stones have evidence of idiopathic hypercalciuria, the most common metabolic abnormality in stone-formers. In the general population without kidney stones and without first-degree relatives with stones, the prevalence is approximately 5% to 10%.
People with idiopathic hypercalciuria have lower bone density and a higher incidence of fracture than their normocalciuric peers. This relationship has been observed in both sexes and all ages. Idiopathic hypercalciuria has been noted in 10% to 19% of otherwise healthy men with low bone mass, in postmenopausal women with osteoporosis, and in up to 40% of postmenopausal women with osteoporotic fractures and no history of kidney stones.
Hypercalciuria is defined as:
- Greater than 250 mg/day (> 4.1 mg/kg/day) in estrogen-replete women
- Greater than 300 mg/day (> 5.0 mg/kg/day) in estrogen-deprived women.
Twenty four hour urine collection is recommended. Random urine calcium to creatinine ratio correlates poorly with 24-hour urine criteria for hypercalciuria and have poor sensitivity and specificity for hypercalciuria.
Reference
Ryan FE and Ing SW, Idiopathic hypercalciuria: Can we prevent stones and protect bones? Cleveland Clinic Journal of Medicine. 2018 January;85(1):47-54
