The answer maybe as simple as his diet. His protein level is slightly low. If the diet is very low in protein and high in fat, the liver can become fatty and congested putting stress on the intrahepatic biliary system.
You didn't list the ALT or AST, but these would also tend to be slightly elevated as well. Doing followup blood tests would be the natural course of action. If the diet could be improved, and changes reflected in follwup blood labs, then that might be an answer..
Ultrasound tests are pretty straight forward, but some children may not think so.