Objective: Rheumatoid nephropathy is one of the most severe extra-articular manifestations of rheumatoid arthritis (RA) associated with a very unfavorable prognosis. This study aimed to identify changes in renal function and morphological variations of kidney diseases in RA patients.

Methods: The study enrolled patients (126 patients) between 18 and 55 years of age with a confirmed active RA of more than 12 months. Each patient underwent the following range of laboratory and instrumental research methods: general clinical analysis of blood and urine, performing urinalysis according to Nechiporenko method; determining daily proteinuria; determining the blood content of glucose, urea, creatinine, uric acid, total bilirubin, liver transaminase level, ionogram, lipidogram, and coagulogram; determining the blood content of rheumatoid factor, anti-streptolysin O, and C-reactive protein; and X-ray of the joints of hands and feet. Renal function was examined by estimating glomerular filtration rate, tubular reabsorption index, and renal functional reserve. For studying the morphological changes in the kidneys under ultrasound examination, renal biopsy was performed in 31 patients with RA with urinary syndrome (proteinuria more than 0.3 g per day and hematuria).

Results: Nephropathy in RA is characterized by impaired renal function and manifested by an increased blood creatinine and a decrease in glomerular filtration rate and renal functional reserve. Among morphological variations of nephropathy at RA, mesangial proliferative glomerulonephritis prevails, accounting for 48.4% of patients. Other disorders include the secondary amyloidosis (29.0% of patients), tubulointerstitial nephritis (16.1%), membranous glomerulonephritis (3.2%), and focal-segmental glomerulosclerosis (3.2%).

Conclusion: Kidney damage is a common systemic manifestation of RA with a long and active course, a major nephropathy trigger.