When you have a routine urine test and some of the results are abnormal, don’t be nervous, but combine it with the presence or absence of your symptoms. This is because routine urine testing is influenced by many factors. For example: how the specimen was left, how long it was left, and the effects of medications. The following are the effects of medications on the results. Vit C: false negative for GLU, BLD, BIL and NIT; Chlorpromazine: false + for BIL; Levodopa: false negative for GLU; false + for KET; Gentamicin: false negative for GLU; Cephalosporin antibiotics: false + for KET; Furantadine: false + for WBC; Bleach: false + for BLD, GLU and WBC; Formalin. False + WBC and false negative occult blood; Neosporin: False + PRO.