Defining hypercalciuria in nephrolithiasis.

Area of Science:

• Nephrology
• Metabolic Bone Diseases

Background:

• The traditional definition of hypercalciuria (≥200 mg/day) is based on controlled diets, but random dietary data complicate its validity.
• Hypercalciuria is a risk factor for nephrolithiasis (kidney stones).

Purpose of the Study:

• To determine the validity of the classic definition of hypercalciuria by analyzing urinary calcium excretion under controlled dietary conditions.
• To assess if hypercalciuria can be reliably defined when extraneous dietary influences are minimized.

Main Methods:

• Retrospective analysis of 39 publications involving urinary calcium excretion data.
• Inclusion of data from non-stone formers, patients with absorptive hypercalciuria type I, and stone formers without absorptive hypercalciuria.
• Evaluation of data from studies utilizing a constant, restricted diet (low calcium, sodium, animal protein).

Main Results:

• On a restricted diet, mean urinary calcium in non-stone formers was below 200 mg/day (upper limit 219 mg/day).
• Patients with absorptive hypercalciuria type I consistently showed mean urinary calcium exceeding 200 mg/day (combined mean 259±55 mg/day).
• Receiver operating characteristic (ROC) curve analysis identified an optimal cutoff of 172 mg/day for urinary calcium on a restricted diet.

Conclusions:

• The classic definition of hypercalciuria (around 200 mg/day) remains valid when dietary variables are controlled.
• A clear distinction in urinary calcium excretion exists between individuals with absorptive hypercalciuria type I and normal individuals under restricted dietary conditions.
• Controlled dietary intake supports the diagnostic utility of the traditional hypercalciuria threshold in nephrolithiasis evaluation.