Urine nephrin concentration in patients with RA and proteinuria was 6.2 ( 3.0 ; 8.8 ) ng/ml and significantly differed in its levels both in controls - 3.6 ( 2.4 ; 5.3 ) ng/ml ( p = 0.03 ) and RA patients without proteinuria - 3.2 ( 2.1 ; 5.1 ) ng / ml ( p = 0.015 ) group .