Wbc/leukocytes constantly in urine, but never nitrites or bacteria. antibiotics don't help. if not uti then what? is endometriosis possible?

Clean catch: Have a clean catch or catheter obtained urine specimen to ensure that no vaginal exudate contaminates the urine specimen causing white blood cells to be seen under the microscope.

Would have blood: interstitial cystitis is an autoimmune disease of the bladder wall that does this. http://emedicine.medscape.com/article/2055505-overview

WBC in urine: I have seen U/A with trace of small WBC and no growth on urine culture in women who have had vaginitis with either mycoplasma, ureoplasma , BV, trichamonas, yeast ( though with yeast/trichamonas they get itching). I usually treat with Zithromax/Flagyl/ Gynezole-1 or doxycycline/flagyl/gynezole-1 . Dont know correlation with endometriosis, as that is more internal. Discuss with doctor