Nhớ phần in đậm viết nghiêng thôi nhé!
ở USA, 15-63% Bn sỏi thận có giảm citrat niệu. Và nó liên quan đến pathophysiology của 1/3 số BN này đấy.
I) Overview of Hypocitraturia
Citrate is the anion of citric acid, a weak acid that is ingested in the diet and produced endogenously in the tricarboxylic acid cycle. The mean urinary citrate excretion is 640 mg/d in healthy individuals. Hypocitraturia usually is defined as citrate excretion of less than 320 mg per day, but this definition has been challenged as inadequate for recurrent stone formers.
Optimal daily urinary citrate levels for calcium stone formers would probably range from 500-800 mg, and one group uses 450 mg/d in men and 550 mg/d in women as cutoff values in stone formers.
The treatment of hypocitraturia should be aimed at correcting the underlying disorder that reduces urine citrate. Approximately 80-90% of patients with hypocitraturia are treated successfully with potassium citrate to raise their urine citrate levels.
Importance of Citrate
Citrate plays several important roles in the mechanism of urinary stone formation.
- Complexing to ion calcium in the urine, lowering the urinary supersaturation of calcium phosphate and calcium oxalate.
- Citrate has a direct inhibitory effect on the crystallization and precipitation of calcium salts.
- Reducing the expression of urinary osteopontin, which is an important component of the protein matrix of urinary stones.
- Increasing urinary pH, which is a factor in uric acid crystallization and uric acid stone formation.
III) Etiology of Hypocitraturia
Acid-base status plays the most significant role in citrate excretion. Alkalosis enhances citrate excretion, while acidosis decreases it.
The following are causes of hypocitraturic calcium nephrolithiasis:
• Distal renal tubular acidosis (RTA)
• Chronic diarrheal syndrome
• Thiazide diuretic or acetazolamide administration
• Diet high in animal protein
• Strenuous physical exercise
• High sodium intake
• Gout or gouty diathesis
• Active UTI
IV) Severity-based Treatment Specifications
Severe hypocitraturia (<100mg/d)
• Chronic diarrheal states - Liquid formulation of potassium citrate
• Complete distal RTA - Potassium citrate 20-40 mEq PO 2-4 times daily
• Infection stones (magnesium and ammonium phosphate or carbonate apatite) - Potassium citrate, antibiotics, stone removal
With regard to struvite (infection) stones, potassium citrate should be used cautiously in these situations, because alkalinization will increase the formation of these stones.
Mild to moderate hypocitraturia (100-320 mg/d)
Caused by diet - potassium citrate (initial dose 20 mEq PO bid-tid) and dietary restriction of animal protein. An adequate fluid volume needs to be maintained, even if this means dilution of the citrate concentration.
Low-normal urinary citrate level (320-400 mg/d)