Upper abdominal pain, yellow skin (hands, feet, face, eyes are white), yellow loose stools. Bilirubin normal, hida, abdominal ct, stool tests clean. This done by gi. What areas to investigate further?
Liver tests, enzymes. It's important to do liver function tests to check for hepatic injury or involvement as this can help discern the cause of the pain and yellow skin. Enzymes, especially pancreatic enzymes are also useful to help rule out pancreatitis, etc.. There are other important markers, like hepatitis antigen/antibody(s), and anti-mitochondrial antibodies for primary biliary cirrhosis. Liver biopsy also.
Probably not GI... You're not describing jaundice, so unless you have sebaceous adenomas (torre's syndrome) you likely don't have a GI problem. Systemic disorders can be characterized by yellow-colored skin plaques or papules--hyperlipidemia (xanthomas), gout (tophi), diabetes (necrobiosis lioidica), pseudoxanthoma elasticum, myeloma (normolipemic flat xanthomas can be >12cm in size on upper trunk & neck). Be well--.