Written by Vivian Lei
Obtaining blood cultures after administration of antibiotics in severe sepsis decreases sensitivity of blood cultures.
Why does this matter?
When treating patients with sepsis, there is an inherent tension between timing of antibiotic administration and obtaining blood cultures. We know delaying antibiotics increases mortality. However, this study supports the importance of collecting blood cultures before antibiotic administration to aid in ultimate diagnosis and treatment.
Best chance of positive blood cultures is before antibiotics
In this prospective multicenter observational trial, researchers obtained blood cultures before and after initiation of antibiotics in patients with severe manifestations of sepsis (SBP < 90 mmHg or lactate >4 mmol/L). Out of 325 enrolled patients in 7 different emergency departments, 31.4% had a positive blood culture before antibiotics versus 19.4% after antibiotics. Sensitivity of post-antibiotic cultures was calculated to be 52.9%, using pre-antibiotic cultures as the gold standard. When including cultures obtained from other sources, sensitivity increased only marginally to 67.6%. This seems to confirm a long-held belief that giving antibiotics before drawing blood cultures will make it harder to identify the offending organism. However, it also confirms that antibiotics work and should not be withheld if cultures are delayed.
See why EMNerd says this study should not change our current practice.
Blood Culture Results Before and After Antimicrobial Administration in Patients With Severe Manifestations of Sepsis: A Diagnostic Study. Ann Intern Med. 2019 Sep 17. doi: 10.7326/M19-1696. [Epub ahead of print]
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Reviewed by Thomas Davis