Blood test
Blood Culture
A blood culture is a test that checks whether bacteria or other germs are growing in your blood. It is used to diagnose serious infections such as sepsis.
Quick answer
Blood Culture: what it is and what the results mean
A blood culture takes a sample of blood and places it in special bottles to see whether germs grow. It identifies bloodstream infection and which antibiotics will work.
- Why it is done: It is used when a serious infection or sepsis is suspected — for example with a high fever, chills or feeling very unwell — to find the responsible germ and guide the right antibiotic.
- Understanding results: If germs grow, the result identifies them and shows which antibiotics are effective, allowing treatment to be targeted.
What it is
A blood culture takes a sample of blood and places it in special bottles to see whether germs grow. It identifies bloodstream infection and which antibiotics will work.
Why it is done
It is used when a serious infection or sepsis is suspected — for example with a high fever, chills or feeling very unwell — to find the responsible germ and guide the right antibiotic.
What to expect
Blood is taken from a vein, often from more than one site, with careful cleaning of the skin to avoid contamination. It is frequently done alongside other blood tests when someone is unwell.
Understanding the results
If germs grow, the result identifies them and shows which antibiotics are effective, allowing treatment to be targeted. Cultures take time to grow, so early treatment is often started before the final result and adjusted later.
Good to know
Risks and limitations
The blood test is safe. Occasionally skin bacteria contaminate a sample, giving a misleading result, which is why samples are taken carefully and interpreted alongside the clinical picture.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Blood Culture: frequently asked questions
How long do blood culture results take?
Germs need time to grow, so results usually take a day or more, with final identification and antibiotic sensitivities taking longer. Treatment is often started before results and refined once they are back.
What does a positive blood culture mean?
It means germs were found growing in the blood, indicating a bloodstream infection. The result identifies the germ and guides antibiotic choice, though occasional contamination is considered when interpreting it.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Relevant royal college / professional body
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