What clinical feature distinguishes hemolytic anemia from biliary atresia?

The presence of splenomegaly is a distinguishing clinical feature between hemolytic anemia and biliary atresia. In hemolytic anemia, the destruction of red blood cells leads to increased workload on the spleen, often resulting in splenomegaly. This is due to the compensatory hyperplasia of the splenic reticuloendothelial system as it attempts to filter and destroy the elevated numbers of lysed red blood cells.

In contrast, biliary atresia is primarily a liver condition that leads to cholestasis due to the absence or obstruction of bile ducts. While patients with biliary atresia can present with hepatomegaly, splenomegaly can be less common or not typically pronounced.

The other options — appearance of the liver, serum bilirubin levels, and onset age of jaundice — might not specifically differentiate between the two conditions in a definitive way. For instance, both conditions can present with elevated serum bilirubin levels, although the type may vary (indirect in hemolytic anemia versus direct in biliary atresia). Hence, the presence of splenomegaly serves as a more definitive distinguishing feature in this context.