UTI: Home, or Hospitalization?

When diagnosed with a uti (via urine sample only), do the doctors run any other actual tests to determine if the patient should be hospitalized and given IV antibiotic treatment, verses just giving antibiotics to take at home? Several weeks ago I had symptoms of a kidney infection(including fever, severe flank pain) and this was all in one day. I didn't go to the doctor that day, and the symptoms have worn off since then. I went to the doctor recently and was diagnosed with uti via urine sample, and given antibiotics to take at home. However I read/was told that those particular symptoms I had weeks ago can signify that the infection,is more serious. Like hospitalization serious, and possibly also be septic(infection spreading to blood). So just because I no longer had the severe kidney pain(now it's just a slight dull ache) or a fever anymore when I actually went to the doctor, I am given the impression by the doctors that it must not be serious enough to be double-checked, let alone hospitalized. Can't they do actual test to tell if it's either reached my kidneys or bloodstream? Or is also having a fever at the time they see you the only way they'll even pay attention to check in the first place?