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
A 6 month old infant is brought with a history of constipation and excessive sleepiness. On exmination, he is lethargic, has periorbital puffines, large tongue and umbilical hernia. The investigation which will help to diagnose this condition is ? 
Select and explain. 
A. T4 TSH assay, B. Karyoptyping, C. Rectal mucosal biopsy, D. Knee X ray
A: T4 TSH assay
Answer: A: T4 TSH assay 
Explanation: Ans. is 'a' i.e., T4 TSH assary o It is typical presentation of hypothyroidism.