The urinary tract infection is likely the cause of the alkaline urine and crystals (if they are struvite crystals).
“Urine pH
Urine pH is typically acidic in dogs and cats and alkaline in horses and ruminants, but varies depending on diet, medications, or presence of disease….. A bacterial urinary tract infection with a urease-producing microbe will result in alkaluria. Urine pH will affect crystalluria because some crystals, such as struvite, form in alkaline urine….. http://www.merckvetmanual.com/mvm/clinical_pathology_and_procedures/diagnostic_procedures_for_the_private_practice_laboratory/urinalysis.html
