REN and rapidly progressive glomerulonephritis: If there is suspected renal involvement, a kidney biopsy is recommended in adults with (i) renal function impairment, (ii) persistent proteinuria >1 g/day despite the use of renin–angiotensin–aldosterone system (RAAS) inhibitors, and (iii) nephrotic or nephritic syndrome, or rapidly progressive glomerulonephritis [35,55].