The urine-blood PCO gradient as a diagnostic index of H(+)-ATPase defect distal renal tubular acidosis.
BACKGROUND
Urine pH during acidemia and urine PCO2 upon alkalization both may be useful to indicate H+ secretion from collecting ducts. The urine anion gap has been used to detect urinary NH4+ for differential diagnosis of hyperchloremic metabolic acidosis. We have previously demonstrated that the lack of normal H(+)-ATPase may underlie secretory defect distal renal tubular acidosis (dRTA). In this study we evaluated the diagnostic value of the urine-blood (U-B) PCO2 in H(+)-ATPase defect dRTA, and compared it with that of urine pH and urine anion gap during acidemia.


METHODS
In H(+)-ATPase defect dRTA, the diagnostic values of three urinary parameters were evaluated: (1) urine pH measured after acid (NH4Cl) loading; (2) urine-to-blood carbon dioxide tension gradient (U-B PCO2) during alkali (NaHCO3) loading; and (3) urine anion gap during acidemia. Seventeen patients were diagnosed as having H(+)-ATPase defect dRTA based on reduced urinary NH4+ and an absolute decrease in H(+)-ATPase immunostaining in intercalated cells on renal biopsy. Eight patients with non-dRTA renal disease served as control patients.


RESULTS
Upon NaHCO3 loading, U-B PCO2 was < or =30 mm Hg in all 17 dRTA patients and >30 mm Hg in all 8 control patients. With NH4Cl loading, urine pH was >5.4 in 15 of 17 dRTA patients and < or =5.4 in 7 of 8 control patients, and the urine anion gap was >5 mmol/L in 13 of 17 dRTA patients and< or =5 mmol/L in 6 of 8 control patients. Therefore, the sensitivity and specificity of U-B PCO2 < or =30 mm Hg during NaHCO3 loading were both 100%, whereas those of urine pH >5.4 or urine anion gap >5 mmol/L during NH4Cl loading were below 90%. In control patients, the U-B PCO2 was found to be well correlated with the urinary NH4+ (r= 0.79, P < 0.05).


CONCLUSIONS
The U-B PCO2 during NaHCO3 loading is an excellent diagnostic index of H(+)-ATPase defect dRTA.
Kim
Sejoong
S
Department of Internal Medicine, Seoul National University, Clinical Research Institute of Seoul National University Hospital, Seoul, Korea.
Lee
Jay Wook
JW
Park
Junghwan
J
Na
Ki Young
KY
Joo
Kwon Wook
KW
Ahn
Curie
C
Kim
Suhnggwon
S
Lee
Jung Sang
JS
Kim
Gheun-Ho
GH
Kim
Jin
J
Han
Jin Suk
JS
D000141:Acidosis, Renal Tubular / Q000097:blood / Q000175:diagnosis* / Q000473:pathology / Q000652:urine; D000328:Adult; D000643:Ammonium Chloride; D000838:Anions / Q000378:metabolism; D002245:Carbon Dioxide / Q000097:blood* / Q000652:urine*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex / Q000201:enzymology / Q000473:pathology; D006180:Proton-Translocating ATPases / Q000172:deficiency* / Q000378:metabolism; D017693:Sodium Bicarbonate
D000838:Anions; D000643:Ammonium Chloride; D002245:Carbon Dioxide; D017693:Sodium Bicarbonate; D006180:Proton-Translocating ATPases