American Board of Internal Medicine (ABIM) Certification Practice Exam

What are the hallmark findings on urinalysis for patients with interstitial nephritis?

1. Hematuria and proteinuria

2. Sterile pyuria and leukocyte casts

3. High urine osmolality

4. Crystals and eosinophils

The correct answer is: Sterile pyuria and leukocyte casts

In the context of interstitial nephritis, the hallmark findings on urinalysis include sterile pyuria and leukocyte casts. Interstitial nephritis, an inflammatory condition affecting the kidney interstitium, typically presents with an influx of white blood cells, particularly eosinophils, which are often seen in the urine. However, what primarily characterizes the urinalysis in this condition is the presence of leukocyte casts. These casts indicate that the inflammation is occurring in the renal interstitium, which can be a result of various causes, including drug reactions, infections, or autoimmune diseases. Sterile pyuria refers to the presence of white blood cells in the urine without bacterial infection, which aligns with interstitial nephritis since it suggests inflammation rather than infection. The leukocyte casts further support that the inflammation is localized to the kidney, specifically in the renal tubules, corroborating the diagnosis of interstitial nephritis. In contrast, other findings mentioned in the options, such as hematuria and proteinuria, may occur in various kidney pathologies but are not specific to interstitial nephritis. High urine osmolality usually suggests conditions like prerenal azotemia or dehydration rather than interstitial nephritis. Crystals and eosin