It is caused by high levels of bilirubin. Urine appears dark yellow or brown, because excess bilirubin in the bloodstream passes through the kidneys. Because of the back-up of bile, an enlarged liver is noticed. The liver is no longer soft. Because the liver isn't functionally properly, it is common to see an enlarged spleen.
Diagnosis is made by several different factors.
CBC refers to Complete Blood Count. LFTs refer to Liver Function Tests. These tests rule out hepatitis or other causes of jaundice in the infant. An operation is then performed to examine the liver and bile ducts. This will confirm the diagnosis of biliary atresia.