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Idiopathic hypercalciuria
Insights
Idiopathic hypercalciuria, a cause of kidney stones, involves increased intestinal calcium absorption. Further research is needed to understand its genetic and environmental factors and optimize treatment.
Area of Science:
- Nephrology
- Endocrinology
- Metabolic Bone Disease
Background:
- Idiopathic hypercalciuria (IH) affects 50% of patients with calcium oxalate/apatite nephrolithiasis.
- IH is a significant risk factor for kidney stone formation.
- Patients with IH typically do not have hypercalcemia or other secondary causes of hypercalciuria.
Purpose of the Study:
- To investigate the mechanisms underlying idiopathic hypercalciuria.
- To explore the role of intestinal calcium absorption and vitamin D metabolism in IH.
- To identify potential contributing factors and therapeutic strategies for IH.
Main Methods:
- Characterization of urinary calcium excretion levels.
- Assessment of serum calcium, parathyroid hormone, and phosphate levels.
- Measurement of serum 1,25-dihydroxyvitamin D concentrations and urinary hydroxyproline excretion.
Main Results:
- Elevated intestinal calcium absorption is the primary driver of increased urinary calcium in IH.
- Serum 1,25-dihydroxyvitamin D levels are often normal to elevated, suggesting dysregulated vitamin D activation.
- Negative calcium balance and increased urinary hydroxyproline indicate potential bone involvement.
Conclusions:
- Idiopathic hypercalciuria is characterized by increased intestinal calcium absorption and potentially altered vitamin D regulation.
- Further research is needed to elucidate the genetic and environmental factors contributing to IH.
- Optimizing therapeutic interventions, including diuretics and phosphate supplementation, requires prospective studies.
Abstract:
Idiopathic hypercalciuria, defined as the urinary excretion of more than 300 mg. calcium per day in men or more than 250 mg. calcium per day in women, or more than 4 mg. calcium per kg. per day, is observed in about 50 per cent of the patients with calcium oxalate/apatite nephrolithiasis and is one of the risk factors for stone formation. These patients do not exhibit hypercalcemia, elevated serum parathyroid hormone concentrations or urinary cyclic adenosine monophosphate excretion nor clinical evidence of sarcoidosis, other granulomas or a malignancy. Hypophosphatemia may be present. Augmented rates of intestinal absorption of dietary calcium account for most of the increments in urinary calcium. Serum 1,25-dihydroxyvitamin D concentrations are in the upper normal range or elevated among many patients and are normal but not suppressed in the others. Activation of 1,25-dihydroxyvitamin D formation may be secondary to hypophosphatemia or other, as yet undefined, factors. Since, 1,25-dihydroxyvitamin D apparently can up-regulate its own receptor, small increments in its synthesis and blood levels could amplify the effect of the hormone to stimulate intestinal calcium absorption. Calcium balances are slightly but significantly negative and urinary hydroxyproline excretion may be increased so that a generalized disorder of calcium homeostasis also involving bone may be present. Additional studies are required to determine the genetic basis for the occurrence of idiopathic hypercalciuria in families, the cause of greater expression of idiopathic hypercalciuria in men and whether environmental factors (high dietary sodium chloride, protein and purified carbohydrate intakes) contribute to the expression of idiopathic hypercalciuria. Although thiazide diuretics, inorganic phosphate, magnesium hydroxide and potassium citrate have provided effective therapy, prospective studies are needed to determine optimum therapy and the optimum duration of treatment.