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Medline ® Abstract for Reference 33

of 'Etiology and diagnosis of distal (type 1) and proximal (type 2) renal tubular acidosis'

The urine-blood PCO gradient as a diagnostic index of H(+)-ATPase defect distal renal tubular acidosis.
Kim S, Lee JW, Park J, Na KY, Joo KW, Ahn C, Kim S, Lee JS, Kim GH, Kim J, Han JS
Kidney Int. 2004;66(2):761.
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.
Department of Internal Medicine, Seoul National University, Clinical Research Institute of Seoul National University Hospital, Seoul, Korea.