A B S T R A C T BACKGROUNDTakayasu arteritis (TA) is the most common cause of renovascular hypertension in young Asians. We wanted to assess endothelial function in patients with TA using flow-mediated vasodilation (FMD) and its correlation with plasma levels of reactive nitrogen intermediates (RNI). METHODSTwenty patients with TA and 20 age-and sex-matched controls were studied. After obtaining informed consent, a detailed clinical examination and appropriate laboratory investigations were performed to assess disease activity (active and inactive groups as per American College of Rheumatologists criteria), FMD (measured as per the guidelines) and levels of RNI were measured. RESULTSThe mean RNI level of patients with TA was 22.54 μM, which was significantly higher than that of controls (5.53 μM) (p<0.0001). The mean RNI level in patients with active disease (16 of 20 patients) was 26.97±17.43 μM, which was significantly higher than their counterparts in remission (12.21±11.82 μM). However, the post hoc analysis of RNI levels did not demonstrate any statistically significant difference between patients with inactive disease and controls (p= 0.36). The mean FMD in patients with TA was found to be 25.72% compared with 24.83% in controls (p>0.05). CONCLUSIONSEndothelial function, as measured by FMD, showed no difference between patients with TA and controls; however, mean RNI level was significantly elevated in patients with TA. Interestingly, patients with active TA had significantly higher RNI levels than those with inactive disease.