A 36-year-old man with fever and a history suggesting typhoid fever; which laboratory test is most critical to establish or exclude the diagnosis?

• A. Sputum cultures
• B. Blood cultures
• C. Stool cultures
• D. Urine cultures

Answer: (D)

Salmonella typhi is most reliably detected when it’s circulating in the blood during the febrile illness. Blood cultures have the highest yield for confirming typhoid fever in the early stage, making them the key test to establish or exclude the diagnosis. Stool cultures can become positive later in the course of disease when the bacteria are shed in the gut, but they’re less useful for early confirmation. Urine cultures are not routinely relied upon because their diagnostic yield for typhoid is lower. Bone marrow culture, while the most sensitive overall, is invasive and not commonly used as the first test. So, drawing blood for culture is the best initial test to diagnose typhoid fever.