Hi, thanks for using healthcare magic
I am sorry that your father in law feels so unwell.
Loss of appetite and unintentional weight loss
in an elderly persons is concerning. The investigations whether blood or imaging, would be focusing on ruling out any evidence of malignancy.
The CT scan
would be looking for any masses present.
The doctors may also suggest blood tests such as a full blood count to check for anemia
in light of his easy fatigue
I hope this helps