Are you talking about dipstick urinalysis? If so then they are only considered a side-room screening test. If you're talking about a urine microscopy & culture, then it would be close to impossible to have normal results while having UTI (ie. normal white cells, no blood, no increased protein, no abnormal culture).
We see this in peds sometimes (in babies specifically)--babies' relative urine output is much higher than adults. The urine just doesn't sit in the bladder for that long, so the LE and nitrite can be negative because it takes time for these to turn positive in the setting of bacteruria. Hence we always send a UA and a UCx, cause you can't necessarily rely on the UA results. I'd think this would be pretty uncommon in adults, though.
If a patient's symptoms are consistent with a UTI, but their dipstick is completely negative, I'd order a urine microscopy and a C&S. I'd hold off on antibiotics, however, until the results came back.
Sensitivity information is usually available from the manufacturer of the urinalysis kit.
UTI-like symptoms can be caused by a varity of other things, such as dietary irritants, concentrated urine, urethral irritation from BV or candidiasis, topical irritants (detergents, etc.), atrophic vaginitis (in postmenopausal women), urethritis, urethral strictures, bladder stones, bladder polyps, bladder carcinoma, overactive bladder, interstitial cystitis, etc.
If the urine culture is negative, you've gotta keep looking.