Interstitial Eosinophils

Prominent interstitial eosinophils (see arrow) are most often associated with allergic-type acute interstitial nephritis (AIN).  However, interstitial eosinophils are not specific for allergic-type AIN as they may also be prominent in other acute and chronic diseases affecting the tubulointerstitium.  Diabetic patients, for example, may have prominent interstitial eosinophilic aggregates, which are usually not associated with medication use or a history of allergy (see Dai DF et al.  Interstitial eosinophilic aggregates in diabetic nephropathy: allergy or not? Nephrol Dial Transplant. 2015 Aug;30(8):1370-6).  Remember, too, that urine eosinophils can be found in a variety of upper and lower urinary tract diseases as well, including infection, cholesterol microemboli, and papillary necrosis (see Nolan CR et al.  Eosinophiluria.  Clin Lab Med 1988; 8:555-565