Which statement is not correct regarding blood cultures?

• A. Blood drawn for culture may be allowed to clot
• B. Two or three blood cultures are recommended as optimum
• C. Collection of 10-20 mL per culture for adults is recommended
• D. Volume of blood cultured is more critical than timing of culture

Answer: (A)

The main idea here is that blood cultures depend on capturing circulating bacteria by placing blood directly into culture bottles that contain growth media and an anticoagulant. Allowing the blood to clot defeats this process because a clot can trap bacteria and prevent them from entering the broth, which lowers the chance of detecting an infection and can lead to false negatives. So drawing blood for culture should be done into sterile bottles without letting it clot.

Two or three separate culture sets are recommended to improve sensitivity and help distinguish true infection from contamination that might come from the skin. This is especially important because bacteremia can be intermittent, and multiple draws increase the likelihood of catching organisms in the sample.

For adults, collecting a substantial volume per culture set is key—for example, around 20 mL per set, typically divided between an aerobic and an anaerobic bottle. More volume per culture enhances the probability of recovering organisms present at low levels.

While timing matters—ideally, cultures are drawn before antibiotics when possible—the volume of blood obtained is a bigger driver of yield than the exact moment of collection.