Acute interstitial nephritis (AIN) is clinically suspected when a patient presents with acute renal failure, exposure to an offending drug, and sterile pyuria. (See "Clinical manifestations and diagnosis of acute interstitial nephritis".)
Activation of eosinophils and other mononuclear white cells plays a significant role in the pathophysiology of AIN [1-3], and case series describe the presence of eosinophils in the renal interstitium on histological examination along with macrophages, lymphocytes, and plasma cells [4,5]. The demonstration of urinary eosinophils has been proposed as a noninvasive test to aide in the diagnosis of AIN.
Eosinophils can be detected in the urine by applying stains that attach to their cytoplasmic granules. The three most commonly used stains are the Wright's, Giemsa, and Hansel's stains, and the latter is the most effective at staining eosinophils in the urine [6,7]. The presence of more than 1 percent eosinophils of the total white cells in the urine is considered a positive test by any of these three stains.
However, the available data suggest that the presence of urinary eosinophils lacks the necessary test characteristics to definitively confirm or exclude a diagnosis of AIN.
Eosinophiluria can be found in a variety of conditions other than acute interstitial nephritis, including transplant rejection, pyelonephritis, prostatitis, cystitis, atheroembolic disease, and rapidly progressive glomerulonephritis [8-10]. As an example, eosinophiluria was demonstrated to be present in 4 percent of 148 consecutive hospitalized patients with pyuria (>5 white blood cells per high power field), none of whom was clinically suspected to have AIN . Among 51 patients who were suspected to have AIN, eosinophiluria was present in 6 of 15 (40 percent) patients with a confirmed diagnosis of AIN and 10 of 36 (30 percent) with another renal diagnosis. Another report suggests that eosinophiluria is found in 90 percent of individuals with an ileal conduit .