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Distal renal tubular acidosis in primary Sjögren syndrome
© Both et al; licensee BioMed Central Ltd. 2012
Published: 28 November 2012
Primary Sjögren syndrome (pSS) is a chronic inflammatory disorder characterized by lymphocytic infiltration of exocrine glands. pSS can also cause distal renal tubular acidosis (dRTA). dRTA is a disorder in which patients are unable to acidify their urine because of impaired hydrogen ion secretion in the collecting duct.
To determine the prevalence of dRTA in pSS using a urinary acidification test.
Patients and methods
62 pSS patients and 27 healthy controls participated in the study. After baseline measurements, both groups received a single administration of 40 mg furosemide and 1 mg fludrocortisone after which urine pH was measured hourly for six hours (Walsh et al., Kidney Int 2007). dRTA was initially defined as a failure to achieve a urine pH < 5.3.
At baseline, pSS patients had a significantly higher urine pH (6.2 ± 0.6 vs. 5.8 ± 0.7) and lower estimated ammonium secretion (10 ± 14 vs. 25 ± 23 mmol/l) than controls (p < 0.01 for both), already suggesting a subtle acidification defect in pSS. Only 4 pSS patients, however, had overt metabolic acidosis (serum bicarbonate < 21 mmol/l). During the test, 24 pSS patients (39%) failed to acidify their urine to a pH < 5.3.
Seven controls (26%), however, were also unable to reach a urine pH < 5.3 (p = 0.3). Therefore, we believe a urine pH of 5.3 may not be sufficiently specific for diagnosing dRTA in pSS. All controls did reach a urine pH of 5.8 or lower during the test. Setting the threshold at this level, 7 patients with pSS (11%) were diagnosed with dRTA.
The prevalence of dRTA in pSS is relatively high. A urinary acidification test is more sensitive to diagnose dRTA in pSS than serum bicarbonate, but the threshold for a positive test should be set at a urine pH of 5.8 instead of 5.3.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.