Blood Culture

Sample
- 5 to 10 ml of blood of the patient is needed, the best time is during fever. This is collected in the culture bottle.
- It is better to get three samples during fever. These samples may be taken from both arms.
- In continuous bacteremia like endocarditis, the timing of the sample is not important.
- In the case of intermittent bacteremia, take a sample at the start of fever, continue up to three sample sin 24 hours.
- Clean the site to avoid contamination by 70% Alcohol.
- Then clean by the 2% iodine.
- If the patient is sensitive to iodine, then cleaning with alcohol is enough.
- Then clean by the 2% iodine.
- For fever of unknown origin draw two blood samples.
- A quantity of less than one ml is insufficient to detect bacterial infection.
- This culture needs at least 72 hours for the report.
- Blood with or without microorganism is collected into bottles for growth in an aerobic or anaerobic environment.
Indications
- Blood culture is advised when there is suspicion of bacteremia or septicemia.
- Find a bacterial infection that has spread into the blood, such as meningitis, osteomyelitis, pneumonia, a kidney infection, or sepsis.
- To find the type of bacteria on culture.
- Find a fungal infection, such as yeast, in the blood.
- Check for endocarditis, which is an infection of bacteria living on the valves of the heart.
- Find the best antibiotics to kill the bacteria. This is called sensitivity testing.
- Find the cause of an unexplained fever or shock.
- In an unexplained fever of several days duration.
- In patients with chills.
- Infected burn.
- urinary tract infection.
- Postoperative wound sepsis.
- Indwelling venous or arterial catheter.
- If bacteria are found in the culture, another test is often done to find the best antibiotic that will kill the bacteria. This is called sensitivity or susceptibility testing.
- Sensitivity testing is important to treat the blood infection properly. This also helps prevent bacteria from becoming resistant to antibiotics.
Blood culture facts:
- This test is done to find the bacteria in the blood (bacteremia).
- Bacteremia may be:
- Intermittent.
- Transient.
- Except in endocarditis or suppurative thrombophlebitis.
- An episode of bacteremia is followed by:
- Chills.
- Fever.
- This is the best time to take the blood sample.
Procedure
- Make the fresh blood film to rule out parasites like malaria, Borrelia, and Trypanosoma.
- The technique for the collection of blood for culture:
- Clean the skin from where the blood is taken.
- Can clean the skin with Betadine and then with 70% ethanol.
- Let the skin dry.
- Clean the top of the culture bottle with betadine.
- This may be followed by 70% alcohol and let it dry.
- Take 10 to 15 mL of the blood from different sites.
- Discard the needle and attach the new sterile needed to inject the blood in the culture bottle.
- Inoculate the anaerobic bottle first then the aerobic bottle.
- Mix gently after the inoculation.
- Clean the skin from where the blood is taken.
- Multiple blood samples are taken. Usually, two to three samples are adequate.
- Take the blood sample when the patient has a high fever or shivering.
- If one sample is positive and the other is negative will indicate contamination.
- If both culture media shows the same growth of bacteria, indicates bacteremia.
- If the patient is taking antibiotics, it should be reported to the lab.
- In this case, take a blood sample in resin, which will inhibit the effect of the antibiotics for the growth of bacteria.
- Take the blood sample before the next dose of antibiotics is given.
- Culture from the I/V catheter is always contaminated and should be avoided.
- The only culture from the I/V catheter can be done if the catheter sepsis is suspected.
- Some lab prefers multiple sites to collect the blood. They take blood at various intervals of 0, 30 and 90 minutes.
- Multiple sites rule out skin contamination.
- Three blood sample culture yield is 99.9%.
- Sample more than 3 does not improve positivity.
- In the case of an adult take 10 mL of blood per bottle.
- Some lab prefers 10 to 15 mL of the blood from all the sites.
- Less than a 5 ml sample of blood shows a less positive yield of culture.
- Discard the syringe needle and use a new sterile needle to transfer the blood into the blood culture bottle.
- Culture the blood aerobically and anaerobically.
- First, add the blood to anaerobic media.
- Gently mix the blood with blood culture media.
- Subculture these samples for at least 72 hours.
Result
- Negative culture report when all cultures and subcultures and gram stains smears are negative.
- The blood culture report may be reported negative after 5 to 7 days of incubation.
- Bacteria need at least 24 hours to grow in the lab.
- By then a preliminary report can be given.
- 48 to 72 hours are needed to identify the organism.
- Anaerobic organisms take a longer time.
- Bacteria need at least 24 hours to grow in the lab.
- The virus can not be detected by blood culture.
- Definitive diagnosis is made in:
- Subacute bacterial endocarditis.
- Salmonellosis (Typhoid fever).
- Brucellosis.
- Gonococcal infection (Gonococcemia).
- Chronic meningococcemia.
- Tularemia.
- Form of rat-bite fever.
Keep in mind:
- When the first tube shows growth and the second tube is negative, then presume that the first tube may be contamination.
- When both tubes show the growth that indicates bacteremia.
- If the patient is taking antibiotics then take the blood before the next dose of antibiotics.
A positive culture report may show:
- Bacteroides.
- Brucella
- Enterobacteriaceae.
- Pseudomonas aeruginosa.
- H. influenzae.
- Listeria monocytogenes.
- Enterococcus.
- Streptococcal pneumoniae.
- Candida albicans.
- Clostridium perfringens.
- Staphylococcus aureus.
- Staphylococcus epidermidis.
- Streptococcus species ( Beta -hemolyticus ).
- Positive blood culture for definitive diagnosis is seen in:
- Subacute bacterial endocarditis.
- Salmonellosis (typhoid fever).
- Brucellosis.
- chronic meningococcemia.
- Gonococcal infection (gonococcemia).
- Tularemia.
- Positive blood culture for definitive diagnosis is seen in:
The person with sepsis may have:
- Fever and chills.
- Less frequent urination.
- Nausea.
- There may be rapid breathing and tachycardia.
- Confusion.
- There may be a drop in blood pressure.
- There may be a failure of one or more organs.