Hypocitraturia as a biomarker of renal tubular acidosis in patients with Sjögrens disease

Abstract

Introduction: Sjögren's disease (SD) is an immune-mediated chronic inflammatory disease that affects epithelial tissues, especially salivary and lacrimal glands, as well as extra glandular manifestations. The main renal manifestation is tubulointerstitial nephritis (TIN), which may present clinically as renal tubular acidosis (RTA). Urinary citrate may be an early biomarker of RTA in these patients. The aim of this study was to evaluate whether hypocitraturia is a predictive biomarker of ATR in a sample of patients with SD in a tertiary hospital in southern Brazil. Methods: All patients with SD who met the inclusion and exclusion criteria and participated in the rheumatology outpatient clinic at Irmandade Santa Casa de Misericórdia of Porto Alegre were included. Demographic data, SD data, and serological and urinary data were obtained. Patients who persistently had urinary pH above 5.5 underwent a urine acidification test with furosemide and fludrocortisone. Continuous variables with a normal distribution were expressed as the mean and standard deviation. The others were expressed as medians and interquartile ranges. Categorical variables are expressed as numbers and frequencies. The association between hypocitraturia and ATR was assessed using the chi-square test. Results: Forty-two patients were included, 95.2% female with a median age of 61.73 years. The prevalence of complete distal RTA was 4.88%. Twenty-eight patients underwent urine acidification testing. Five patients had hypocitraturia, and two of them had complete distal RTA. The association between hypocitraturia and ATR was statistically significant (p< 0.012), with a sensitivity of 100%, specificity of 91.2% and accuracy of 91.7%. The negative predictive value was 100%. The renal evaluation of the population demonstrated, in addition to two patients with ATR, one patient with impaired renal function and six patients with proteinuria greater than 0.5 g/24 hours. Conclusion: The prevalence of ATR in the studied population was 4.88%. Hypocitraturia had high sensitivity and accuracy for the diagnosis of ATR.