URINARY ACIDIFICATION AND RHEUMATOID-ARTH RITIS

The aim of this study was to investigate subclinical abnormalities in renal function suggestive of incomplete distal renal tubular acidosis (DRTA) in patients with rheumatoid arthritis (RA), using the gradient between PCO2 in urine and blood (U-B PCO2 gradient), which is a simple and sensitive test. We prospectively selected 45 patients in three gr oups (G). G 1 (n = 15p), with RA, mean age 44 years and mean disease d uration 6.5 years. G2 (n = 10p), with RA and Sjogren's syndrome (SS), mean age 47 years and mean disease duration 6.6 years. G 3 (n = 20) he althy volunteers, no history neither renal nor rheumatic diseases, mea n age 37 years. Patients in G1 and G2 had no history of concurrent dis ease affecting renal parenchyma, their acid-base status and renal funt ion were normal (Creatinine clearence above 70 ml/ min/1.73m(2)). All patients received NSAIDs but none gold salts and/or D-Penicillamine. T he ability to acidify the urine was evaluated in ail cases by U-B PCO, (2) gradient, after a 500 ml NaHCO3 continuous infusion 1 molar soluti on through a peripheral vein. U-B PCO2 lower than 30 was considered pa thological and diagnostic for DRTA. The urinary specimen for pH and PC O2 were kept under mineral oil and processed within 5 minutes of excre tion. The blood samples for PCO2 were obtained from a peripheral vein and measured after obtaining a urinary pH 7.8 or above, pH and PCO2 we re measured with a BMS 3 MK2 Radiometer, Copenhagen Denmark electrode and analizer. The U-BPCO2 results were ((x) over bar 2 sd): G1 = 47 +/ - 26, G2 = 49.8 +/- 8.4; G3 = 52.5 +/- 12.2. There were no statistical differences among the three groups (F = 1,228727). In the G1, a singl e patient presented U-B PCO2 lower than 30 (U-B PCO2 = 5), having a lo ng active disease at the evaluation time. In G2 and G3 no gradient alt erations were recorded. We conclude, in spite of the fact that U-B PCO 2 gradient is a very useful and sensitive tool for detecting dRTA, tha t there was no corelation between incomplete type dRTA and RA or betwe en incompleta dRTA and RA associated to SS. In addition, no associatio n was found between NSAID intake and dRTA.