Fluid in Abdomen

I have a 9 year old Staffie that recently started to look a bit round. I didn’t like the look of it and had a previous dog with hemangiosarcoma so I took him straight to the vet once I realized this wasn’t just a bit of gas or weight gain. The vet did a very quick ultrasound and confirmed there was fluid and took a sample to send off for cytology. She also did an xray which she didn’t really mention seeing much of note and took a blood and urine sample. She did mention that she thought his liver looked slightly enlarged. Cytology came back and there wasn’t any cancer cells found. Bloodwork looked mostly normal. He is on a renal diet and had good improvement in his creatinine from his last blood work up in January. She said liver enzymes were slightly elevated and in an otherwise healthy dog she’d think nothing of it. She mentioned there was a small amount of protein in his urine but didn’t give a specific amount. My dog has been acting completely normal. Eating and drinking normally, enthusiastic, sleeps peacefully, goes to the bathroom just fine.

We have an appointment scheduled in a few weeks with an internal medicine specialist. It was the soonest we could get. Any clues what we could be dealing with? I’m concerned about the distended belly and just want to be sure we’ll be okay waiting the 3.5 weeks until his appointment.