This is for informational purposes only. For medical advice or diagnosis, consult a professional. A blood culture test is a laboratory test to check for the presence of bacteria or other microorganisms in a blood sample. It's used to diagnose bloodstream infections, also known as bacteremia or septicemia, which can be serious. Why is a blood culture test done? To diagnose bloodstream infections: Symptoms of a bloodstream infection can include fever, chills, rapid heart rate, and confusion. To identify the specific organism causing the infection: This helps doctors choose the most effective antibiotic or other treatment. To monitor the effectiveness of treatment: Repeat blood cultures may be done to ensure the infection is clearing.