I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
Q- An 18-year-old woman with sickle cell disease is brought to the emergency department by her parents because of a 2-hour history of severe abdominal pain and nausea. Her parents say that she had a cheeseburger, milk shake, and chocolate bar for lunch. Her temperature is 37°C (98.6°F). Physical examination shows tenderness over the right upper quadrant of the abdomen, radiating to the right shoulder. Ultrasonography of the right upper quadrant of the abdomen shows gallstones.
Which of the following is the most likely underlying cause of this patient’s current condition?
(A) Decreased hepatic secretion of lecithin
(B) Decreased reabsorption of bile salts
(C) High ratio of cholesterol to bile acids in bile
(D) Infestation with parasites secreting β-glucuronidase
(E) Overload of unconjugated bilirubin
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Answer
Sickle cell disease leads to chronic hemolysis due to the destruction of abnormally shaped red blood cells. Hemolysis increases the release of heme, which is converted to bilirubin. Excess bilirubin can overwhelm the liver’s conjugating capacity, leading to an increase in unconjugated bilirubin in the blood. The unconjugated bilirubin is excreted into bile, where it can precipitate as calcium bilirubinate to form pigment gallstones. These stones are common in patients with chronic hemolysis, such as those with sickle cell disease. This patient has symptoms consistent with gallstone-related complications, such as biliary colic or acute cholecystitis. Ultrasonography confirms the presence of gallstones, linking her condition to the increased production of bilirubin secondary to hemolysis.
The correct answer is E