Urinary excretion of nephrin in rheumatoid arthritis patients with proteinuria

To investigate urine excretion of nephrin in patients with proteinuric nephropathies associated with rheumatoid arthritis (RA).

We enrolled in the study 42 patients with seropositive RA and proteinuria, the control group (20 persons) was formed from healthy blood donors, the comparison group (23 persons) was formed from RA patients without proteinuria. Kidney biopsy was performed in 26 patients (glomerulonephritis was diagnosed in 14 patients, АА-amyloidosis in 7 patients and tubulointerstitial nephritis in 5 patients).

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. In RA patients with proteinuria, we found a positive correlation between urine nephrin and protein concentrations (r=0.4; p=0.04). Urine nephrin levels in patients of the glomerulonephritis - 7.3 (5.9; 9.2) and amyloidosis groups - 6.9 (3.9; 9.8) ng/ml were higher than in the controls (p=0.001; p=0.04) and in the group of patients without proteinuria (p=0.005; p=0.03). In the patients with tubulointerstitial nephritis urine nephrin concentration did not differ significantly with the values in both the control and the RA patients without proteinuria groups.

According to our data, proteinuria in the overall cohort of patients with seropositive RA is associated with increased levels of urine nephrin excretion, the highest levels of nephrin excretion were registered in patients with glomerulonephritis and amyloidosis.