In neonatal cholestasis, if the serum gamaglutamyl-transpeptidase (gamma GTP) is more than 600IU/L the most likely diagnosis is:

GGTP of more than 600IU/L is suggestive of cholestasis. 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 5-40IU/L. Ref: Harrison's Principles of Internal Medicine, 17th Edition, Page 1998 ; O P Ghai Essential Pediatrics, 6th Edition, Page 174 ; Surgery of Liver, Bile Duct and Pancreas in Children By Edward Howard and Stringer 2nd, Page 112 ; Liver Disorder in Childhood By Alex P. Mowat