What is a Blood Culture?

This test is advisable when there are symptoms of blood infection such as septicemia or bacteremia and blood culture is done to identify the bacteria or other microorganism. A blood microbial culture will be requested by your doctor depending on your case history and clinical findings upon physical examination.

Collection of Specimen

About 10 ml (0.3 fl oz) of blood is withdrawn with a needle and syringe from a vein, either on the inside of the elbow or back of the hand, and collected in two vials. It is sent to the laboratory where it is placed on a petri dish with agar. This is the ideal medium for bacterial growth and after incubation, it will indicate clear areas of bacterial growth if there was bacteria present in the blood specimen.

A blood culture is done mainly for bacteria and if any growth is seen, further tests are done to identify the type of bacteria. A gram stain may be done using special types of stain to identify different organisms. Certain microorganisms pick up and retain the purple color and are called gram-positive organisms, while other organisms lose the purple stain and retain the red stain and are called gram-negative. No special preparation is needed before a blood culture and there is not much discomfort except for the needle prick.

A normal value means that no organism could be grown in the laboratory and hence there is no infection in the blood, while a positive result will show the growth and multiplication of organisms in the specimen. Treatment can then be commenced according to the micro-organism identified and the sensitivity or action of various drugs on it. Three blood cultures may need to be done to confirm results because of variable bacterial infection in the blood.

Blood Culture Report

The initial or preliminary report will indicate if any bacteria have been found and results should be available within a day, depending on the country or laboratory. The final report will show the type of bacteria and its sensitivity to antibiotics, and this may be available after five to seven days.


Further Reading :
  • Sputum or Phlegm Bacteria Culture Lab Test
  • Microbial Culture Lab Test for Bacteria, Fungus