Contamination: This is often the most common reason for a urine sample showing a high white blood cell (WBC) count but a negative culture. Contamination can occur during the collection process, especially if the genital area is not properly cleaned before collecting the sample.

Intermittent Bacteriuria: The bacteria may be present in the urine only intermittently, leading to a negative culture despite the presence of WBCs.
Fastidious Organisms: Some bacteria, such as Chlamydia or Ureaplasma, may not grow on standard urine culture media, leading to a negative culture result despite infection.
Tubulointerstitial Nephritis: This condition, often caused by an allergic reaction to certain medications (like NSAIDs or certain antibiotics), can cause inflammation in the kidneys, leading to WBCs in the urine without a positive culture.
Urolithiasis (Kidney Stones): The presence of kidney stones can cause inflammation and lead to WBCs in the urine, even in the absence of infection.

Tuberculosis (TB) of the Urinary Tract: Although rare, TB can infect the urinary tract and cause a high WBC count in the urine with negative standard bacterial cultures. It's crucial to consider this diagnosis, especially in high-risk populations.
Malignancy: Certain cancers, like bladder or renal cancer, can cause inflammation and lead to WBCs in the urine. While less common, missing a diagnosis of cancer can have severe consequences.
Obstructive Uropathy: Conditions that obstruct the flow of urine, such as kidney stones or tumors, can lead to inflammation and WBCs in the urine without infection.

Malakoplakia: A rare inflammatory condition that can affect the urinary tract and cause WBCs in the urine.
Sarcoidosis: A systemic disease that can cause granulomatous inflammation in various parts of the body, including the kidneys, leading to WBCs in the urine without infection.
Fungal Infections: In immunocompromised patients, fungal infections of the urinary tract can occur and may not be detected by standard bacterial cultures.