What laboratory findings are indicative of acute interstitial nephritis (AIN) related to drug use?

Acute interstitial nephritis (AIN) is a condition characterized by inflammation of the renal interstitium, often due to drug reactions, infections, or autoimmune diseases. When considering laboratory findings indicative of AIN related to drug use, the presence of urinary eosinophils and white blood cell (WBC) casts is significant.

In AIN, the immune response to the offending drug can lead to the attraction of eosinophils to the renal interstitium. Eosinophils in the urine are a classic finding following exposure to drugs such as penicillins, non-steroidal anti-inflammatory drugs (NSAIDs), or diuretics. Additionally, the presence of WBC casts indicates that there is inflammation affecting the renal tubules, further supporting the diagnosis of AIN. These findings are crucial as they help differentiate AIN from other types of acute kidney injury, such as acute tubular necrosis or prerenal azotemia, which have different causes and management strategies.

The other laboratory findings associated with acute kidney conditions can be important but do not specifically point to AIN related to drug use as clearly as eosinophils and WBC casts do. For instance, high blood urea nitrogen and creatinine