What is the best method to diagnose lactase deficiency?

• A. Hydrogen breath test
• B. Plasma aldolase level
• C. LDH level
• D. D-xylose test

Answer: (A)

Lactase deficiency is diagnosed by assessing whether lactose is properly digested in the small intestine. When lactase is deficient, lactose isn’t broken down and reaches the colon, where bacteria ferment it and produce hydrogen. The hydrogen breath test measures how much hydrogen appears in the breath after a lactose load, so a rise above baseline indicates malabsorption due to lactase deficiency. This test directly reflects the physiological process of lactose digestion and is noninvasive, making it the most appropriate tool. Other options don’t target lactose digestion: plasma aldolase or LDH are general tissue damage markers, not specific to disaccharide digestion; the D-xylose test assesses overall intestinal absorption, not lactase enzyme activity.