A 15-year-old otherwise healthy boy presents with a complaint of intermittent abdominal distention, crampy abdominal pain, and excessive flatulence. He first started noticing these symptoms when he moved into his father’s house, and his stepmother insisted on milk at dinner every night. He has normal growth, has not lost weight, and has no travel history. Which of the following is the most appropriate diagnostic study to diagnose his condition?

a. Barium swallow and upper GI

b. Hydrogen excretion in breath after oral administration of lactose

c. Esophageal manometry

d. Stool pH

e. Serum lactose levels

the answer is below…

The United States Medical Licensing Examination, or USMLE for short, is a three-part licensing examination that is required in order to receive a license to practice medicine within the United States.

The USMLE assesses a physician’s ability to apply knowledge, concepts, and principles, and to determine fundamental patient-centered skills that are important in health and disease and that constitute the basis of safe and effective patient care.Examination committees composed of medical educators and clinicians from across the United States and its territories prepare the examination materials each year.

This exam is designed by the Federation of State Medical Boards and the National Board of Medical Examiners to determine whether or not an individual understands and can apply the knowledge necessary to practice medicine safely and intelligently.

The USMLE is actually comprised of three different exams that are referred to as steps, which examine the individual’s knowledge of specific topics related to the field of medicine such as basic science, medical knowledge, medical skills, clinical science, and the application of all of these skills and areas of knowledge in the medical field.

All three steps of the USMLE include a series of computerized multiple-choice questions, but the format of the exam and the information covered in each multiple-choice section is different for each step of the USMLE. The USMLE Step II also has a clinical skills portion that examines an individual’s ability to work with real patients and the USMLE Step III has a computerized patient simulation portion in addition to the multiple-choice section of the exam. In order for an individual to receive a license to practice medicine, the individual must pass all three steps of the USMLE.

Medical doctors with an M.D. degree are required to pass this examination before being permitted to practice medicine in the United States of America

The correct answer is b; Hydrogen excretion in breath after oral administration of lactose.[2]

Lactase is a disaccharidase localized in the brush border of the intestinal villous cells. It hydrolyzes lactose to its constituent monosaccharides, glucose and galactose. Intestinal lactase levels are usually normal at birth in all populations; however, lactase deficiency is a common, genetically predetermined condition. Lactase activity is not readily increased by the oral administration of substrate or the inclusion of lactose in the diet. The clinical symptoms of lactose malabsorption are due to the presence of osmotically active, undigested lactose, which may act to increase intestinal fluid volume, alter transit time, and produce the symptoms of abdominal cramps, distention, and occasionally, watery diarrhea. Bacterial metabolism of the nonabsorbed carbohydrates in the colon into carbon dioxide and hydrogen may contribute to the clinical symptoms. Acquired lactase deficiency is often associated with conditions of the gastrointestinal tract that cause intestinal mucosal injury (e.g., sprue and regional enteritis). Diagnostic techniques for lactose intolerance include removal of the offending sugar, with a reproduction of symptoms upon reintroduction. Although the ingestion of even small amounts of lactose can be diagnostic if gastrointestinal symptoms occur, the measurement of breath hydrogen is more specific, as it is not affected by glucose metabolism or gastric emptying. Similarly, an acidic stool pH in the presence of reducing substances would be diagnostic. Direct measurement of enzyme levels combined with histologic evaluation helps to differentiate an acquired (secondary versus primary) lactase deficiency in which the intestinal histology is normal.