I'm going to be in the minority with this take, but I'd actually recommend being cautious about pursuing an MRI/CT right away unless someone suffered a traumatic acute injury with significant neurological symptoms (e.g., cauda equina, gross strength loss, etc). There is very little to no correlation between severity of symptoms and findings on diagnostic tests for low back pain, and a lot of medical professionals start chasing MRI/CT findings instead of just addressing the symptoms. Retrospective studies show people getting advanced diagnostic tests for an acute onset of low back pain take longer to recover from their injury and cost significantly more money to treat.
Research also shows there's one thing that determines whether or not someone will get a fusion. It has nothing to do with severity of pain, symptom distribution, neurological findings, size of herniations, etc... the one thing is your zip code. If your local specialist likes to perform fusions as a treatment option instead of the absolute last resort as it's intended you're much more likely to get one whether or not you actually needed it.