Which finding confirms IgA nephropathy on diagnostic studies?

• A. Decreased serum creatinine
• B. Positive IgA mesangial deposits on immunostaining
• C. Normal urinalysis
• D. Anti-nuclear antibodies

Answer: (B)

IgA nephropathy is diagnosed by identifying IgA-containing immune complexes deposited in the glomerular mesangium on kidney biopsy using immunofluorescence. This mesangial IgA deposition is the hallmark that confirms Berger disease, distinguishing it from other causes of nephritis. Clinically, patients often have episodic gross hematuria, sometimes following mucosal infections, but serum creatinine levels may be normal early on and urine analysis can vary. Other antibodies like ANA point toward different autoimmune conditions and are not specific for IgA nephropathy. Thus, the most confirming finding is positive IgA staining in the mesangium on immunostaining.