Confused about blood cultures?

[Maria1308]

Hello was wondering if I could get someone to help me understand blood cultures and contaminants. I’m a fairly new nurse working in the hospital setting and took care of an adult patient who was admitted to the hospital for bacteremia. Pt was admitted for fever (unsure of the temp), back ache, and headache. A set of blood cultures were drawn and the patient was discharged on amoxicillin. Well patient was called to come back bc the second blood culture grew out gram negative cocci. The patient no longer had any of the ssx she’d originally came in for with the exception of HA and back pain but was admitted anyway bc of the blood culture and receivers antibiotics. All other labs were normal and she remained afebrile. The night nurse came in and after giving report to her, she stated that she felt that it may have been a contaminant bc it was gram negative rods. My question is how do you determine if a blood culture is a contaminant?? Is gram negative rods a rare blood culture result.

Attending thought the same and reordered a blood culture draw.

Blood cultures always confuse me.

[MunoRN, RN]

By "second blood culture" are you referring to one of two sets drawn at the same time, or blood cultures drawn well after the start of treatment?

Good practice is usually to draw two sets from different sites to help differentiate between bacteremia and a contaminated culture. If both sets are positive with the same bug then contamination is less likely. Typically if the patient is responding to treatment then there is no indication for follow up blood cultures.

Gram negative rods are not a particularly unusual culprit of bacteremia. E coli is not an unusual cause of UTIs which can move into the bloodstream, it can also infect the blood through GI tract abnormalities. Typically it's skin flora that is suspicious for a contaminated blood culture.