Blood cultures are one of the most important diagnostic tests when sepsis or other severe systemic infections are suspected. The purpose is to detect bacteria or fungi in the bloodstream – something that should not normally occur.

How are blood cultures analyzed?

When blood cultures are taken, the blood is placed in special bottles which are then placed in a warming cabinet. There, they are continuously monitored to see if microorganisms grow. If bacteria or fungi proliferate, the system will detect it, and the sample proceeds to cultivation and resistance testing.

Blood cultures must not delay treatment

Because the analysis takes time – often 1–2 days before preliminary results are available – we cannot use blood cultures to decide whether antibiotic treatment should be started. In cases of suspected sepsis, treatment should always be initiated immediately, based on clinical findings.

The basis for targeted antibiotic treatment

However, the blood culture is very valuable afterward. Once the microbe is identified, antibiotic treatment can be adjusted more precisely, and the use of broad-spectrum agents can be reduced. This is crucial both for patient safety and for preventing antibiotic resistance.

How to take blood cultures correctly?

Correct sampling is crucial to avoid false positive results.
Here are the main points:

• Thoroughly disinfect the skin before sampling to prevent contamination.
• Take two sets of blood cultures from different venipuncture sites, preferably with 10–20 minutes in between. This increases the chance of detecting true bacteremia.
• Samples should be taken before starting antibiotics, if possible without delaying treatment.

Blood cultures are a simple but powerful test that – when taken correctly – can be crucial for accurate diagnosis, targeted treatment, and improved patient outcomes.