This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pediatrics
Differential cyanosis occurs in 
Select and explain. 
A. PDA, B. TGA, C. Tricuspid stenosis, D. VSD
A: PDA
Answer: A: PDA 
Explanation: Differential cyanosis is present when the preductal (right upper extremity) oxygen saturation is higher than the postductal(lower extremity) saturation.ETIOLOGY:- PDA with reversal of shunt.- Persistent pulmonary hypeension of the newborn.Reverse differential cyanosis:In this condition only the upper pa of the body is cyanosed and the lower pa is pink.ETIOLOGY:PDA +TGV+severe pulmonary hypeensionPDA+TGV+preductal coarctation of the aoa