A 21-year-old man presents with flatulence, abdominal pain, and diarrhea for the last 2 years. He has noticed that these symptoms occur after drinking milk or eating yogurt. The diarrhea is nonbloody, watery, and explosive. The patient denies fever, chills, or weight loss. Physical examination is unremarkable.
Which of the following is the best next step in the diagnostic workup of this patient?
A. Acid steatocrit testingHydrogen breath test. The patient in this question is presenting with classic findings associated with lactose intolerance, a condition in which individuals have insufficient levels of lactase. Lactase is an enzyme that breaks down lactose into glucose and galactose, permitting carbohydrate absorption. If patients are unable to hydrolyze lactose, they develop diarrhea, bloating, and flatulence. The most accurate test is the hydrogen breath test, in which the hydrogen level is measured in one’s breath after lactose ingestion. If the lactose cannot be digested, enteric bacteria metabolize it and produce hydrogen that is detected in the test. (A) Acid steatocrit testing evaluates for fat malabsorption; however, lactose intolerance involves carbohydrate malabsorption. (C) The patient in this question is not febrile and is not showing signs of infection, so blood cultures are not warranted. (D) Intestinal biopsy is sometimes performed after hydrogen breath test confirms elevated hydrogen levels. However, this is not the best initial step in diagnosis.