What Is a Blood Culture Test?

What it means

Blood is usually free of germs. For a blood culture, blood is drawn into special bottles filled with liquid food for germs, then kept warm in the lab to see if anything grows. Bottles are usually taken in pairs, one for germs that need oxygen and one for germs that do not. This test is often done when someone has a high fever or signs of sepsis, a serious reaction to infection that needs urgent medical care.

Blood cultures take time. Many results are reported in stages: "no growth so far" after a day or two, then a final result after about five days. If something grows, the lab first reports what it looks like under the microscope (a Gram stain), then names the germ, and later reports which antibiotics work against it. The team often starts antibiotics before the result is back and adjusts them once it arrives.

A blood culture is different from a blood count. A blood count measures blood cells, while a culture looks for living germs in the blood.

Where you may see it

• Microbiology results in a hospital patient portal
• Emergency department records when infection or sepsis is suspected
• Discharge summaries listing "blood cultures: no growth" or a named germ
• Lab reports that show results from more than one bottle or set