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Medline ® Abstract for Reference 33

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

33
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The urine-blood PCO gradient as a diagnostic index of H(+)-ATPase defect distal renal tubular acidosis.
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Kim S, Lee JW, Park J, Na KY, Joo KW, Ahn C, Kim S, Lee JS, Kim GH, Kim J, Han JS
SO
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.
AD
Department of Internal Medicine, Seoul National University, Clinical Research Institute of Seoul National University Hospital, Seoul, Korea.
PMID