Take-home point: AIN is generally a clinical diagnosis (definitive diagnosis is with kidney biopsy)! Urine eosinophils has poor sensitivity and specificity and is difficult to get (lab often hesitant to run it). If you are worried about AIN, get your renal colleagues involved, remove the offending agent, and start solumedrol early (and plan for a long course)! Early diagnosis and treatment are most important to potentially restoring kidney function.
Bonus PEARL on S. aureus bacteremia: When you get S. aureus bacteremia, ALWAYS treat! Look aggressively for a source to get source control, and always r/o endocarditis (30-40% have this!). As a side note, whenever you have S. aureus bacteremia, consult ID! Here is a slide from Jen Babik’s Hospital Medicine CME last year on the “top 10 ID consults” with a few references at the bottom for further reading:
More on AIN:
- In one recent review, sensitivity and specificity of urine eosinophils for the diagnosis of AIN (biopsy-proven) were 67% and 82%, respectively. (PMID 24052220)
- Prerenal AKI and ATN are the most common forms of AKI in the hospital, but AIN is probably next most common
- Check out “Diagnosing drug-induced AIN in the hospitalized patient: A challenge for the clinician” for more! (PMID 24691017)