Background: In sarcoidosis, renal involvement is less common than lung involvement. Epidemiology and clinical characteristics of the patients with renal involvement are largely unknown.

Methods: From the database of the Japan Renal Biopsy Registry (J-RBR), the patients who were diagnosed with renal involvement of sarcoidosis such as sarcoidosis-related tubulointerstitial nephritis or renal calcinosis were extracted. The prevalence and clinical characteristics of these cases were analyzed. After removing the cases with concomitant glomerular diseases or renal calcinosis, the correlation between urinary protein-creatinine ratio (UPCR) and eGFR or serum albumin levels were evaluated by Pearson's correlation (r). In addition, distributions of serum albumin levels were compared across the categories of urinary albumin levels.

Results: Among the 55,885 participants in the J-RBR database, 135 patients (66 men and 69 women, 0.24% of total registration) had renal involvement of sarcoidosis including nine cases with concomitant glomerular diseases: nephrosclerosis (n = 4), IgA nephropathy (n = 2), diabetic nephropathy (n = 2) and unclassified (n = 1). Mean value (± standard deviation) of age was 62 ± 14, eGFR was 30.7 ± 15.2, and UPCR was 0.50 ± 0.68. Among the patients without any concomitant glomerular disease or renal calcinosis, UPCR was negatively correlated with eGFR (r =  - 0.531, p < 0.001) and serum albumin level (r =  - 0.352, p < 0.001).

Conclusions: Data from a nationwide biopsy registry revealed that main forms of histopathology of renal involvement of sarcoidosis was tubulointerstitial nephritis and these cases were common in older adults. The intensity of the tubulointerstitial nephritis may be related to the degree of renal dysfunction and proteinuria.