Hi Holly,
Kidney disease is said to be quite common in Syrians.
There are numerous kinds of kidney problems but almost all are fatal, I am afraid.
Sometimes, a hamster may have blood in its urine and may have just a simple kidney infection that can be treated with antibiotics. However, in my experience, the infection is often caused by complications that antibiotics cannot cure. But, I always take the hamster to the Vet for an examination and antibiotics just in case it may be cured. Unfortunately, most of my girl's have had to be put down later.
Signs of kidney problems are fluid retention if the kidneys have completely failed. If this happens the hamster needs to go to the Vet immediately, likely to be put to down. Sometimes only one kidney is the problem and the hamster will not swell up with fluid but will stop urinating, eating and drinking and lose weight very quickly. A Vet can feel the size of the kidneys and tell if one or both are involved. A Vet will likely prescribe multiple strong antibiotics.
Kidney disease can't be cured in humans or animals so what I do is to try to prevent or at least put it off by not adding protein to their diet. I stick to grains, veggies and fruits for treats and hope for the best.
Hamstermama