Urine Eosinophilia Testing: Clinical Indications
Urine eosinophilia testing is primarily performed to diagnose acute interstitial nephritis (AIN), where it demonstrates good predictive value, and to evaluate eosinophilic cystitis in patients presenting with irritative urinary symptoms and hematuria. 1
Primary Indication: Acute Interstitial Nephritis
- Urine eosinophilia serves as a good predictor of acute interstitial nephritis, with a sensitivity of 63% and positive predictive value of 50% when using Hansel's stain. 1
- The test should be performed in patients with acute kidney injury of unclear etiology, particularly when drug-induced AIN is suspected. 1
- Hansel's stain is superior to Wright's stain for detecting urinary eosinophils, increasing both sensitivity (63% vs 25%) and positive predictive value (50% vs 25%) for AIN diagnosis. 1
Secondary Indication: Eosinophilic Cystitis
- Urine eosinophilia evaluation is indicated in patients presenting with the classic triad of frequency (67%), dysuria (62%), and gross/microscopic hematuria (68%), particularly when accompanied by suprapubic pain. 2
- Peripheral blood eosinophilia is present in only 43% of eosinophilic cystitis cases, making urine examination an important complementary diagnostic tool. 2
- The diagnosis of eosinophilic cystitis requires cystoscopy with biopsy as the gold standard; urine eosinophilia serves as a supportive finding but cannot establish the diagnosis alone. 2
Clinical Context and Associated Conditions
- Urinary tract infection accounts for 25% of eosinophiluria cases, making it equally common as AIN in patients with detectable urinary eosinophils. 1
- In patients with hypereosinophilic syndrome presenting with urinary symptoms, urine eosinophilia testing helps identify bladder involvement as a manifestation of systemic disease. 3
- Eosinophilic cystitis should be considered in the differential diagnosis when patients present with recurrent urinary retention, particularly in males. 4
Important Diagnostic Caveats
- Only 11% of patients tested for urinary eosinophils will have positive results, indicating this is a relatively specific finding when present. 1
- Positive urine cultures are found in only 26% of eosinophilic cystitis patients, so negative cultures do not exclude the diagnosis. 2
- The presence of urinary eosinophils does not establish parasitic bladder infiltration as the etiology, despite historical suggestions; extensive parasitic workup is rarely positive. 5
Helminth Infection Considerations in Travelers
- In returning travelers or migrants with eosinophilia and urinary symptoms, Schistosoma haematobium infection must be excluded through serology and terminal urine microscopy, as urine dipstick for microscopic hematuria has low sensitivity and should not be relied upon. 6
- Terminal urine collection at midday increases microscopic sensitivity for schistosomiasis, though sensitivity remains too low for microscopy to be used in isolation. 6
- Schistosomiasis can cause obstructive uropathy, bladder stones, and bacterial superinfection, and is linked to squamous cell carcinoma of the bladder in chronic cases. 6