Confused - a and e trip uti

Went an and e thought my son had a uti he held his pee over 12 hours and belly hurt. He did a pee sample. They said no uti. But some white cells. On nhs online it says white cells indicate a uti? Now yesterday my son’s been sick in the morning and before bed. His temp was 37.2 and now at 3am it’s 38?