Blood Culture Test

A blood culture tries to grow bacteria from a blood sample, to find out whether an infection has reached the bloodstream and what organism is causing it. Unlike most blood tests it takes days rather than hours, because something has to be given time to grow.

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What it is

Blood is normally sterile. This test asks whether it still is. A sample is injected into bottles of nutrient broth and kept warm while an instrument watches for signs that something is multiplying. If growth appears, the organism is identified and then tested against antibiotics to see which ones will work. The whole point is the name of the culprit, not a number: knowing which bacterium is in the bloodstream is what lets a broad initial antibiotic be narrowed to a targeted one.

Why it is done

  • To find the cause of a suspected bloodstream infection or sepsis, in someone with fever, chills, a racing heart, confusion or a falling blood pressure
  • To guide antibiotic choice, by identifying the organism and testing what it responds to
  • To check whether an infection has cleared, by repeating cultures after treatment has started
  • To investigate infection of a heart valve, a prosthetic joint or an indwelling line, where the bloodstream is the route to the answer

What to expect

The skin is cleaned carefully first, which matters more here than in an ordinary draw: skin bacteria carried into the bottle produce false alarms. Blood is usually taken from two separate sites, and often a second set is drawn later, because bacteria enter the bloodstream in bursts and one sample can miss them. Automated systems typically incubate bottles for up to five days, though most common organisms declare themselves within about two. Treatment does not wait for the result; antibiotics are usually started on suspicion and adjusted once the culture speaks.

Questions worth asking

  • How many sets of cultures were drawn? Each bottle or set is generally billed on its own, so two sites and two time points can mean four charges.
  • Are organism identification and antibiotic susceptibility testing billed as additional codes once something grows?
  • If a culture turned out to be a skin contaminant, was follow-up testing charged for chasing a false positive?
  • For cultures drawn in an emergency department, is the lab work included in the visit level or itemized separately?

What Blood Culture Test costs by state

Blood Culture Test prices at hospitals

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Sources

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