I am sorry to hear that he has not been feeling well. Is he doing better now?
Just wanted to give some information on transitional cells.
In urinalysis testing (which is where you will identify the cells) there are generally three types of epithelial (surface) cells. One of them is transitional cells. They come from the bladder but may also dome from ureters, the proximal urethra and from the renal pelvis (a part of the kidney where the urine starts). Due to normal turnover (new cells replacing old cells) having a couple cells found in the urine (usually 0-2/hpf) is not unusual. Having greater numbers can be suggestive of degenerative, hyperplastic or neoplastic conditions. The neoplastic (cancerous) condition that we become most concerned about is TTC as mentioned above.
Couple of questions: Have follow up a urinalysis been done? If so, were transitional cells also found there? A consistent finding of transitional cells, even in normal numbers may be of concern depending upon the patient. Finally, has an ultrasound been performed. This would be one of the most important tests in looking for TTC or any other masses. It can also see stones that may invisible on radiographs (X-Rays).
I hope you pet is feeling better. Keep us posted.