A patient presents with intermittent light brown urine and hematuria associated with upper respiratory infections. What immunoglobulin would likely be found in a renal biopsy?

• A. IgA
• B. IgD
• C. IgE
• D. IgM

Answer: (A)

The presence of intermittent light brown urine and hematuria in conjunction with upper respiratory infections suggests a condition known as IgA vasculitis, also referred to as Henoch-Schönlein purpura. This condition is characterized by the deposition of IgA-containing immune complexes in small vessels, leading to systemic symptoms such as skin rash, joint pain, and renal involvement, including glomerulonephritis.

In renal biopsy for this condition, the predominant immunoglobulin observed would be IgA, as it is typically associated with the pathophysiology of IgA vasculitis. The accumulation of IgA in the kidneys correlates with the immunological processes behind the disease, which often manifests after respiratory infections, revealing a possible trigger for the immune response that results in the renal symptoms.

Understanding the relationship between the patient's symptoms and the appropriate immunoglobulin provides insight into the underlying mechanisms of the pathophysiology, reinforcing the association of IgA with renal involvement in this specific type of small-vessel vasculitis.