Several problems can cause fluid to build up in the abdomens of cats or dogs.
Fortunately, one-year-old dogs have low rates of cancer and heart failure. They are the leading causes of abdominal fluid in older dogs, but are very unlikely to be playing a role in your Yorkie’s problems.
Trauma can cause blood or clear fluid to build up in the abdomen. But you don’t mention any traumatic events.
You do, however, mention that your dog has low blood protein levels. Low protein levels can lead to fluid build up in the abdomen through osmotic pressure.
There are three common syndromes that lead to low blood protein. A problem with the kidneys can cause them to excrete excessive protein into the urine. A problem with the intestines can cause them to lose protein into the feces. And a problem with the liver can cause it to produce too little protein in the first place.
A one-year-old Yorkshire Terrier can suffer from any of these problems, but the one that is most likely is inadequate protein production by the liver. Young small dogs are prone to a syndrome called liver shunt.
You should have your dog checked for a liver shunt. The first step in this process is ultrasound of the abdomen by a specialist. Conveniently, the ultrasound also will give insight into the health of the intestines.
I’d recommend that you arrange for an ultrasound as soon as possible. Certain blood tests that check the function of the liver also may be indicated. Finally, to be thorough, I recommend a test for protein in the urine (the test is called the urine protein to creatinine ratio).