Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (541 page)

   Patients with nonspecific signs of renal dysfunction, especially when associated with symptoms of allergic-type reaction after initiation of a new drug therapy. Disease onset ranges from few days to several months following drug exposure.

   The clinical triad of rash, fever, and eosinophilia is found in approximately 10% of patients with acute interstitial nephritis.

   Patients with chronic interstitial nephritis can present with nausea, vomiting, fatigue, and weight loss.

   Laboratory Findings

   
Blood:

   Serum creatinine is increased. Serum IgG is usually increased, and serum complement is normal. Patients with IgG4-related disease may have elevated IgG4 levels.

   CBC may show increased WBCs, neutrophils, and bands. Eosinophilia and increased blood IgE levels are seen in approximately one third of patients. Anemia may be present with no evidence of hemolysis or iron deficiency. Anemia resolves when renal functionn becomes normal.

   Indirect Coombs test is negative, and bone marrow is typically normal.

   
Urine:

   May be oliguric or nonoliguric. Urinary indices similar to those seen in ATN.

   Microscopic hematuria, sterile pyuria, and WBC casts. RBC casts are rare.

   Eosinophiluria (eosinophils >1% of urinary WBCs). Sensitivity of eosinophiluria for the detection of AIN is 40% and the positive predictive value is 38%.

   Proteinuria is usually mild to moderate (<1.0 g/24 hours). Nephrotic-range proteinuria may occur (rare).