Hypercalciuria

Excerpt

Hypercalciuria is generally considered to be the most common identifiable metabolic risk factor for calcium nephrolithiasis. It also contributes to osteopenia and osteoporosis. Its significance is primarily due to these two clinical entities: nephrolithiasis and bone resorption. Calcium-based kidney stones (calcium oxalate and calcium phosphate) account for 85% of all stones. Hypercalciuria is the most significant cause of idiopathic calcium-based kidney stones. On average, hypercalciuric calcium stone formers also have decreased bone mineral density compared to controls who are neither stone formers nor hypercalciuric. Among children with kidney stones, those with hypercalciuria will have average bone calcium density measurements 5% to 15% lower than their normocalciuric peers, and it is unknown what the long-term effects are.

The definition of hypercalciuria can be a bit confusing. Traditionally, it has been defined as daily urinary calcium excretion of greater than 275 mg in men and greater than 250 mg in women. This definition ignores concentration, age, renal function, weight considerations, and the question of whether a different normal excretion standard is reasonable based solely on gender.

Hypercalciuria also can be defined as a daily urinary excretion of more than 4 mg calcium/kg body weight. This definition is more useful in the pediatric age group if the child is over two years old. In adults, it tends to allow higher urinary calcium excretions in heavier and obese individuals compared to lighter patients. One solution is to use the 24-hour urinary calcium concentration (less than 200 mg calcium/liter urine is "normal," but less than 125 mg calcium/liter is "optimal").

Another clinically useful definition, especially in pediatrics, is the random or spot urinary calcium/creatinine ratio—less than 0.2 mg calcium/creatinine mg is normal while less than 0.18 mg calcium/creatinine mg is optimal. The benefit is that it does not require a 24-hour urine collection before every visit to track the hypercalciuria.

Which definition to use depends on the clinical situation and the availability of reliable 24-hour urine collection data. For optimal results, one approach is to look at all definitions and concentrate treatment on optimizing the most serious of them. This "optimization" approach focuses less on what is "normal" and more on the optimal level for a calcium stone-forming patient. This type of optimization can also be used for other urinary chemical risk factors besides hypercalciuria.

Young children and infants tend to have higher urinary calcium excretion and lower urinary creatinine levels, so the suggested normal limits for calcium/creatinine ratios differ by age as follows:

1. Up to six months of age: less than 0.8

1. Six to twelve months of age: less than 0.6

1. 24 months and older: less than 0.2