"UTI" the owner said the previous vet had diagnosed UTI when her guinea pig had passed blood in the urine.
No urine test was taken by the first vet. She wanted another opinion from me.
"UTI is common," I said. "I need to ward it and do a urine collection to check the urine."
How to collect urine from a guinea pig? I remembered my sheep metabolic studies lectures in Animal Nutrition in the 3rd year. That was 4 decades ago. Improvise. I looked for a clean pan, not the usual pee pan. I found two. See images.
Will update later.
Tentative diagnosis is traumatic injury as the guinea pig still has good appetite and has not passed blood in the urine on 2nd day of hospitalisation after being treated with medication.
Image from link from toapayoh vets as blogger.com seems to have some problems in layout when images are posted directly to it.