POS-548 GLOMERULAR FILTRATION STATE OF CHILDREN WITH JUVENILE IDIOPATHIC ARTHRITIS ACCORDING TO Cys-C INDICATORS

Abstract

According to modern literature reveiw, it is believed that about 8% of children with juvenile idiopathic arthritis (JIA) have chronic kidney disease. Subclinical kidney damage in JIA remains undiagnosed in real clinical practice. Kidney damage can manifest itself as a complication of the underlying disease or, as a consequence, its long-term treatment.The structure of renal pathology in JIA is represented by secondary amyloidosis, glomerulonephritis, tubulo-interstitial nephritis. We investigated the level of cystatin C (Cys-C) in the blood of 80 children with JIA. The age of the subjects was from 3 to 17 years. The calculation of the glomerular filtration rate (GFR) was carried out twice (the first and third months of the study) on the basis of the concentration of Cys-C and creatinine in serum according to the methods: Hoek F.J. et al. (2003), Equation based on cystatin C (2012), Schwartz and Counahan-Barratt (2012). Cys-C averaged 0.886 ± 0.1495 (0.84; 0.79-0.98) μg / ml. The average GFR according to the 2012 equation based on cystatin C was 81.04 ± 12.129 (82.92; 71.74-88.53) ml / min / 1.73 m2, which is significantly lower than with the same GFR calculated using the method Hook - 88.81 ± 14.948 (91.05; 77.32- 98) ml / min / 1.73 m2, p <0.01. The percentage below normal GFR calculated using the 2012 equation based on cystatin C was twice that calculated using Hook's formula: 65 (81.3%) versus 33 (41.3%) cases (p <0.001 according to McNemar's test ). Analysis of the frequency of GFR decline, calculated on the basis of creatinine and Cys-C, also revealed a number of significant differences. Thus, the cystatin C-based equation technique compared with Schwartz and Counahan-Barratt 2012 methods overestimated the incidence of GFR abnormalities by 81.3% (p <0.001) and 47.5% (p <0.001), respectively, in the first month of the study and 81 respectively 3% (p <0.001) and 55.0% (p <0.001) in the third month. A similar comparison with Hook's method showed that according to the Schwartz formula, GFR decreased by 41.3% less often (p <0.001) both in the first and in the third month. The Counahan-Barratt formula did not show significant differences in the first study of creatinine (difference 7.5%, p <0.05), and the second study showed that the decrease in GFR according to the Counahan-Barratt was recorded 15.0% less frequently than according to the data on Hook's method - a deviation close to the level of significance, p <0.09. A more subtle method for detecting subclinical kidney damage in children with JIA is to determine the level of cystatin C followed by calculating the glomerular filtration rate, according to Hook's formula. The concentration of Cys-C was directly related to the duration of the use of non-steroidal drugs (ρ = 0.44, p <0.04), thus, the lengthening of their use had a negative effect on GFR (ρ = -0.44, p <0.04) . And, conversely, with an increase in the duration of immunobiological therapy, the level of cystatin C in the blood decreased (ρ = -0.48, p <0.02) and GFR increased (ρ = 0.48, p <0.02). When detecting a decrease in GFR in children with JIA, it is necessary to limit the intake of non-steroidal anti-inflammatory drugs and increase the basic therapy.