In Vivo Renal Tubule pH in Stone-Forming Human Kidneys

Area of Science:

• Nephrology
• Urology
• Biochemistry

Background:

• Patients with ileostomies often form uric acid or calcium oxalate stones.
• Acidic urine in these patients paradoxically leads to calcium phosphate (CaP) and urate crystal plugs in kidney collecting ducts.
• Focal acidification defects in inner medullary collecting duct and Bellini duct (BD) cells are a potential explanation.

Purpose of the Study:

• To investigate focal acidification defects in dilated Bellini ducts (BDs) of patients with ileostomies and stone formation.
• To directly measure intraluminal pH within BDs during percutaneous nephrolithotomy (PCNL).

Main Methods:

• Utilized a fiber-optic pH microsensor to measure intraluminal pH.
• Measurements were taken from the bladder, saline irrigant, and dilated BDs in patients undergoing PCNL.
• Included three patients meeting specific inclusion criteria.

Main Results:

• Bladder urine pH ranged from 4.97 to 5.58; saline irrigant pH ranged from 5.17 to 5.75.
• Intraductal pH measurements were obtained from 11 dilated BDs.
• Mean intraductal BD pH (6.43 ± 0.22) was significantly higher (p < 0.01) than bulk urine pH (5.31 ± 0.22), a difference of over 1 unit.

Conclusions:

• This study provides the first direct evidence of focal acidification defects in injured/dilated human BDs.
• These defects occur despite the production of highly acidic bulk urine.
• Findings may explain the paradoxical formation of CaP and urate plugs in stone-forming patients with ileostomies.