This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
In neonatal cholestasis, if the serum gamaglutamyl–transpeptidase (gamma GTP) is more than 600 IU/L the most likely diagnosis is – 
Select and explain. 
A. Neonatal hepatitis, B. Choledochal cyst, C. Sclerosing cholangitis, D. Biliary atresia
D: Biliary atresia
Answer: D: Biliary atresia 
Explanation: Neonatal cholestasis

Neonatal cholestasis is defined as prolonged elevation of serum levels of conjugated bilirubin beyond the first 14 days of life.
Neonatal cholestasis can be divided into extrahepatic and intrahepatic disease and clinical features of any form of cholestasis are more or less similar.
Neonatal hepatitis is the prototype of intrahepatic cholestasis
Biliary atresia is the prototype of extrahepatic biliary atresia

Enzymes that reflect cholestasis: There are three enzymes that are usually elevated in cholestasis

Alkaline phosphatase → Found in or near bile canalicular membrane of hepatocytes
5' nucleotidase
Gamma glutainyl transpeptidase → Located in the endoplasmic reticulum and in bile duct epithelial cells.


Because GGT is more diffusely localized in the liver, its elevation in serum is less specific than are the elevation of Alkaline phosphatase & 5' nucleotidase.
Nevertheless, the following distinction is worthwhile.

"GGT levels are commonly elevated to values more than 10 times normal in biliary atresia while in hepatic causes it is raised to about three times normal."
Normal values for GGT is about 5-40 IU/L and thus a value of 600 IU/L in the patient in question reflects an elevation of more than ten times the normal value. The patient is thus likely suffering from `biliary atresia'.