This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inborn Errors of Metabolism, Subject name: Pediatrics
Lactose intolerance in a suspected patient is diagnosed by giving an oral load of lactose and measuring concentration of: 
Select and explain. 
A. CO2, B. H2, C. One/two carbon compounds, D. N2
B: H2
Answer: B: H2 
Explanation: b. H2 (Ref: Nelson's 20/e p 2870, Ghai 8/e p 297)Breath hydrogen tests can be used to determine a specific carbohydrate malabsorption.It can be used to diagnose bacterial overgrowth or lactose/fructose malabsorption.