The urine-blood PCO gradient as a diagnostic index of H(+)-ATPase defect distal renal tubular acidosis.

Abstract

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).

CONCLUSION:

The U-B PCO2 during NaHCO3 loading is an excellent diagnostic index of H(+)-ATPase defect dRTA.

• Authors: Sejoong Kim, Jay Wook Lee, Junghwan Park, Ki Young Na, Kwon Wook Joo, Curie Ahn, Suhnggwon Kim, Jung Sang Lee, Gheun-Ho Kim, Jin Kim, Jin Suk Han
• Journal: Kidney international (Kidney Int) Vol. 66 Issue 2 Pg. 761-7 (Aug 2004) ISSN: 0085-2538 [Print] United States
• PMID: 15253731 (Publication Type: Clinical Trial, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Anions
• Ammonium Chloride
• Carbon Dioxide
• Sodium Bicarbonate
• Proton-Translocating ATPases

Topics

• Acidosis, Renal Tubular (blood, diagnosis, pathology, urine)
• Adult
• Ammonium Chloride
• Anions (metabolism)
• Carbon Dioxide (blood, urine)
• Humans
• Hydrogen-Ion Concentration
• Kidney Cortex (enzymology, pathology)
• Proton-Translocating ATPases (deficiency, metabolism)
• Sodium Bicarbonate