What conditions cause low levels of urinary citrate?
Patients with hypocitraturia excrete < 320 mg/day while optimal levels are closer to 640 mg/day. Idiopathic hypocitraturia occurs in < 5% of patients with calcium stones, and secondary hypocitraturia may occur in 30%. Citrate is freely filtered by the glomerulus, 75% is reabsorbed by the proximal renal tubule, and little citrate is secreted. Most secondary causes of hypocitraturia decrease urinary citrate by increasing proximal renal tubular reabsorption. Secondary causes of low citrate include dehydration, high animal protein and low fruit and vegetable intake, metabolic acidosis, hypokalemia, thiazide diuretics, carbonic anhydrase inhibitors, magnesium depletion, renal tubular acidosis, and diarrhea. Diarrhea also causes direct gastrointestinal loss of citrate and magnesium.