Background. In systemic autoimmune diseases of the connective tissue, kidney damage in some cases is a syndrome of the disease, and in others, it is a consequence of the underlying process. Objective: to establish the incidence and nature of violations of kidney function in children and adolescents with juvenile idiopathic arthritis (JIA) and systemic lupus erythematosus (SLE), depending on the duration and activity of the disease. Materials and methods. 113 children aged 7 to 18 years were examined, of which 70 patients with JIA and 43 — with SLE. Distribution to the groups was carried out depending on the duration and activity of the disease. The status of kidney function was evaluated using hemorrhagic tests (serum creatinine level), determination of glomerular filtration rate. We have evaluated the level of proteinuria in the daily urine, as well as studied the concentration function of the kidneys by means of urine analysis according to Zimnytsky. Statistical processing was carried out using the statistical software package Statgra­phics 16.0. Results. Thus, in children with JIA, with the duration of the disease more than 3 years, there was a change in the renal function characterized as proteinuria, and a violation of glomerular filtration rate and a decrease in the concentration function of the kidneys. When studying the incidence of violations depending on the activity of the pathological process, it was established that in the group with 0 degree of activity, both glomerular filtration rate (25.0 %) and concentration function of the kidneys (12.5 %) decreased. In the group with I degree of activity, there was detected microproteinuria (4.4 %), violation of glomerular filtration rate (12.3 %) and decreased renal concentration (6.6 %). In the group with II degree of activity, microproteinuria (14.2 %) and a certain reduction in glomerular filtration rate (14.2 %) were detected, and in the group with III degree of activity, almost all patients had microproteinuria (66.6 %) and a decrease in the concentration function of the kidneys (33.3 %). When studying the function of the kidneys depending on the activity of the pathological process, attention was paid to the increase in the level of microproteinuria (p < 0.01) and reduction of glomerular filtration in the group with III degree of activity (p < 0.01). There is also an increase in the level of proteinuria in the group with the duration of the disease for more than 3 years. Thus, it has been found that kidney damage is associated with a significant decrease in glomerular filtration and proteinuria, that is, a dysfunction of the glomerular kidney system. In patients with SLE, in a group with the duration of the disease from 1 to 3 years, in 68.1 % of cases there was proteinuria, and in rare cases — changes in glome­rular filtration rate. In the group of children with the duration of the pathological process over 3 years, deeper changes in the function of the kidneys have been detected. Thus, almost all patients had proteinuria (90.4 %), the incidence of reduction in glomerular filtration rate increased to 19.0 %, and in 14.2 % of cases, a reduction in the concentration function of kidneys has been detected. When analyzing the incidence of renal dysfunction depending on the activity of SLE, attention was paid to the increase in the level of proteinuria (p < 0.05) and the decrease in glomerular filtration rate (p < 0.02), especially in patients with II degree of disease activity. In the study of kidney function indicators depending on the duration of SLE, it was found that in the group with the duration of the disease for more than 3 years, there was a decrease in glomerular filtration rate (p < 0.03), increase in the level of microalbuminuria (p < 0.03) and a reduction in maximum urinary gravity (p < 0.03). When studying the indicators of kidney function depending on the activity of the pathological process, an increase in the level of microalbumi­nuria with II degree of activity (p < 0.01) was observed. Thus, in almost a third of children with SLE, with a disease duration of more than 3 years and preserved activity of the pathological process, the formation of signs of kidney damage with a dysfunction of both the glomerular and tubular kidney apparatus was detected, which will cause the development of chronic renal failure. Conclusions. In children with JIA and SLE, with disease duration for more than 3 years, impaired renal function is observed in persistent activity of the pathological process. Signs of kidney damage are the presence of proteinuria, reduced glomerular filtration, decreased renal concentration function.

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