However, a more recent 2008 NEJM correspondence by Andrew Fletcher points out that subsequent studies looking at the utility of eosinophiluria to diagnose AIN are problematic. The author points out that at his institution, the sensitivity and positive predictive value of eosinophiluria for AIN were 25% and 3%, respectively. Furthermore, there is a wide variety of other diagnoses that can cause eosinophiluria, not just AIN. A brief differential diagnosis is as follows:
-acute interstitial nephritis
-renal atheroembolic disease
-bladder Schistosoma infection
-rapidly progressive glomerulonephritis
The Fletcher letter implies that based on the severe limitations of using the eosinophiluria to diagnose AIN that it not be used at all. I still use it, though based on these limitations it can probably only be used as an adjunct to make a diagnosis of AIN when trying to differentiate between AIN & ATN, a not uncommon scenario. Any other opinions out there as to how to best use this test?