Blood culture system is a method of testing a sample of your blood for infection. A laboratory technician places your blood in a special dish (culture) that contains an artificial medium that supports the growth of bacteria and some types of fungus. Then, the technician watches to see if any germs grow in the culture. If the results show that you have an infection, your doctor may prescribe antibiotics to treat it.
Blood cultures help your doctor diagnose infections in many parts of your body, such as the lungs, heart, joints, and bones. A blood culture can also show how extensive the infection is and whether it has spread to other parts of your body, including the brain (septic shock). Blood cultures are used to help determine the best course of treatment and to monitor progress during treatment.
Whether a blood culture is helpful or not depends on the ability of your body to fight the infection and how long the organisms are present in your bloodstream. Blood culture sensitivity decreases in certain groups of patients, such as neutropenic cancer patients. Also, blood culture sensitivity can be reduced by repeated blood draws and inadequate sampling.
In addition, a single set of blood cultures may be positive for coagulase-negative staphylococci or Corynebacterium species, which are part of the normal skin flora. Such findings do not necessarily indicate a bacterial bloodstream infection and may instead represent contamination of the specimen by the indwelling catheter or collection process.
A blood culture system consists of two bottles, each filled with 10 mL of blood, one aerobic and one anaerobic. Each order of blood cultures usually requires two samples, taken from different anatomic sites. Ideally, the inoculated blood should not be drawn through an indwelling catheter. The risk of needlestick injury is much greater when using a double-needle technique to draw and inoculate blood cultures, particularly in pediatric patients.
In general, a blood culture takes about 72 hours to detect infection. During this period, a positive blood culture is determined by measuring pressure changes in the headspace of the bottle due to consumption and production of gases by microorganisms.
A blood culture is the cornerstone of diagnosing many infectious diseases, and several methods and commercial systems are available for collecting and detecting disease-causing microorganisms. Recent advances in blood culturing systems have increased the yield of the test, reduced time to organism recovery, and diminished laboratory technologist hands-on time.
Several automated systems have been developed to reduce the number of blood cultures manually inoculated, and these may improve sensitivity. Other advancements include continuous-monitoring blood culture systems such as the Isolator (Wampole), VersaTREK Microbial Detection (Thermo Scientific), BacT/ALERT (bioMerieux), and BACTEC (Becton Dickinson and Company). These systems are designed to maximize recovery of fastidious organisms. However, no system is optimal for detection of all types of microorganisms.