American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the primary basis for diagnosing thin glomerular basement membrane disease?

1. Kidney biopsy findings

2. Persistent hematuria with normal kidney function

3. Family history of kidney failure

4. Elevated serum creatinine levels

The correct answer is: Persistent hematuria with normal kidney function

The primary basis for diagnosing thin glomerular basement membrane disease is the presence of persistent hematuria with normal kidney function. This condition is characterized by a genetic defect affecting the synthesis of type IV collagen, leading to thinning of the glomerular basement membrane. Patients typically present with symptoms, most notably microscopic hematuria, which occurs without significant impacts on kidney function in the early stages. In diagnosing this disease, the finding of hematuria is consistent with the structural changes in the basement membrane, while kidney function tests often remain normal during the early phases, differentiating it from other renal pathologies that can lead to kidney dysfunction or significant proteinuria. Thus, the presence of persistent hematuria alongside preserved kidney function is a strong indicator of thin glomerular basement membrane disease and is critical for its diagnosis. Other aspects, such as kidney biopsy findings, may eventually provide confirmation through histological examination, but the initial diagnosis is typically made based on clinical presentation, specifically the combination of hematuria and normal function. Family history and elevated serum creatinine levels can be relevant in a broader context, but they do not serve as defining characteristics for diagnosing this specific condition.