What is the procedure for obtaining blood cultures in the workup of infective endocarditis (IE)?

Updated: Jan 03, 2019
  • Author: John L Brusch, MD, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
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Never draw only 1 set of blood cultures; 1 is worse than none. Two sets of blood cultures have greater than 90% sensitivity when bacteremia is present. Three sets of cultures improve sensitivity and may be useful when antibiotics have been administered previously.

The AHA (endorsed by IDSA) 2010 guideline update on CIED infections and their management recommends drawing at least 2 sets of blood cultures at evaluation before starting antimicrobial therapy. [43]

For diagnosing subacute IE, draw 3-5 sets of blood cultures over 24 hours. This helps detect 92-98% of cases in patients who have not recently received antibiotics. In the case of acute IE, 3 sets may be drawn over 30 minutes (with separate venipunctures) to help document a continuous bacteremia.

Using various types of blood culture bottles (with resins added to interfere with antibiotic action) probably has little advantage. Some of these may interfere with bacterial growth.

When blood culture results fail to show an infectious agent after blood is drawn 48 hours after antibiotic therapy has been stopped, the second set of blood for cultures must be drawn approximately 7 days later. If these later culture results remain negative, the diagnosis of IE must be reconsidered. In general, blood for culture should not be drawn through intravenous (IV) lines unless this is part of an approach for diagnosing line infection.

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