American Board of Internal Medicine (ABIM) Certification Practice Exam

Which characteristic of non-glomerular hematuria helps differentiate it from glomerular hematuria?

1. Presence of erythrocyte casts

2. Isomorphic erythrocytes in the urine

3. Brown tea-colored urine

4. Significant proteinuria

The correct answer is: Isomorphic erythrocytes in the urine

In differentiating between glomerular and non-glomerular hematuria, one key characteristic is the type of erythrocytes found in the urine. Non-glomerular hematuria often presents with isomorphic erythrocytes, which are typically uniform in shape and size, resembling normal red blood cells. This is in contrast to glomerular hematuria, where dysmorphic erythrocytes are more common due to the fragmentation of red blood cells as they pass through the damaged glomeruli. The presence of isomorphic erythrocytes indicates that the bleeding is originating from a source outside the glomeruli, such as the urinary tract or the bladder. Understanding this distinction is vital in the clinical setting, as it guides further investigation and management of the underlying cause of hematuria. The other characteristics do not serve this specific differentiating role. For instance, erythrocyte casts are associated with glomerular damage and are not found in non-glomerular hematuria. Brown tea-colored urine can occur in both types of hematuria, primarily depending on the concentration of blood or breakdown products, and significant proteinuria is generally indicative of glomerular pathology, rather than being a feature of non-gl