Blood Culture

Sample

1. 5 to 10 ml of blood of the patient is needed, the best time is during fever. This is collected in the culture bottle.
2. It is better to get three samples during fever. These samples may be taken from both arms.
   1. In continuous bacteremia like endocarditis, the timing of the sample is not important.
   2. In the case of intermittent bacteremia, take a sample at the start of fever, continue up to three sample sin 24 hours.
3. Clean the site to avoid contamination by 70%  Alcohol.
   1. Then clean by the 2% iodine.
      1. If the patient is sensitive to iodine, then cleaning with alcohol is enough.
4. For fever of unknown origin draw two blood samples.
5. A quantity of less than one ml is insufficient to detect bacterial infection.
6. This culture needs at least 72 hours for the report.
   1. Blood with or without microorganism is collected into bottles for growth in an aerobic or anaerobic environment.

Indications

1. Blood culture is advised when there is suspicion of bacteremia or septicemia.
2. Find a bacterial infection that has spread into the blood, such as meningitis, osteomyelitis, pneumonia, a kidney infection, or sepsis.

3. To find the type of bacteria on culture.
4. Find a fungal infection, such as yeast, in the blood.
5. Check for endocarditis, which is an infection of bacteria living on the valves of the heart.
6. Find the best antibiotics to kill the bacteria. This is called sensitivity testing.
7. Find the cause of an unexplained fever or shock.
8. In an unexplained fever of several days duration.
   1. In patients with chills.
   2. Infected burn.
   3. urinary tract infection.
   4. Postoperative wound sepsis.
   5. Indwelling venous or arterial catheter.
9. 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.
   1. Sensitivity testing is important to treat the blood infection properly. This also helps prevent bacteria from becoming resistant to antibiotics.

Blood culture facts:

1. This test is done to find the bacteria in the blood (bacteremia).
2. Bacteremia may be:
   1. Intermittent.
   2. Transient.
      1. Except in endocarditis or suppurative thrombophlebitis.
3. An episode of bacteremia is followed by:
   1. Chills.
   2. Fever.
      1. This is the best time to take the blood sample.

Procedure

1. Make the fresh blood film to rule out parasites like malaria, Borrelia, and Trypanosoma.
2. The technique for the collection of blood for culture:
   1. Clean the skin from where the blood is taken.
      1. Can clean the skin with Betadine and then with 70% ethanol.
      2. Let the skin dry.
      3. Clean the top of the culture bottle with betadine.
         1. This may be followed by 70% alcohol and let it dry.
      4. Take 10 to 15 mL of the blood from different sites.
      5. Discard the needle and attach the new sterile needed to inject the blood in the culture bottle.
      6. Inoculate the anaerobic bottle first then the aerobic bottle.
      7. Mix gently after the inoculation.
3. Multiple blood samples are taken. Usually, two to three samples are adequate.
   1. Take the blood sample when the patient has a high fever or shivering.
   2. If one sample is positive and the other is negative will indicate contamination.
   3. If both culture media shows the same growth of bacteria, indicates bacteremia.
   4. If the patient is taking antibiotics, it should be reported to the lab.
      1. In this case, take a blood sample in resin, which will inhibit the effect of the antibiotics for the growth of bacteria.
      2. Take the blood sample before the next dose of antibiotics is given.
   5. Culture from the I/V catheter is always contaminated and should be avoided.
   6. The only culture from the I/V catheter can be done if the catheter sepsis is suspected.
4. Some lab prefers multiple sites to collect the blood. They take blood at various intervals of 0, 30 and 90 minutes.
   1. Multiple sites rule out skin contamination.
   2. Three blood sample culture yield is 99.9%.
   3. Sample more than 3 does not improve positivity.
5. In the case of an adult take 10 mL of blood per bottle.
   1. Some lab prefers 10 to 15 mL of the blood from all the sites.
   2. Less than a 5 ml sample of blood shows a less positive yield of culture.
6. Discard the syringe needle and use a new sterile needle to transfer the blood into the blood culture bottle.
7. Culture the blood aerobically and anaerobically.
   1. First, add the blood to anaerobic media.
8. Gently mix the blood with blood culture media.
9. Subculture these samples for at least 72 hours.

Result

1. Negative culture report when all cultures and subcultures and gram stains smears are negative.
2. The blood culture report may be reported negative after 5 to 7 days of incubation.
   1. Bacteria need at least 24 hours to grow in the lab.
      1. By then a preliminary report can be given.
      2. 48 to 72 hours are needed to identify the organism.
      3. Anaerobic organisms take a longer time.
3. The virus can not be detected by blood culture.
4. Definitive diagnosis is made in:
   1. Subacute bacterial endocarditis.
   2. Salmonellosis (Typhoid fever).
   3. Brucellosis.
   4. Gonococcal infection (Gonococcemia).
   5. Chronic meningococcemia.
   6. Tularemia.
   7. Form of rat-bite fever.

Keep in mind:

1. When the first tube shows growth and the second tube is negative, then presume that the first tube may be contamination.
2. When both tubes show the growth that indicates bacteremia.
3. If the patient is taking antibiotics then take the blood before the next dose of antibiotics.

A positive culture report may show:

1. Bacteroides.
2. Brucella
3. Enterobacteriaceae.
4. Pseudomonas aeruginosa.
5. H. influenzae.
6. Listeria monocytogenes.
7. Enterococcus.
8. Streptococcal pneumoniae.
9. Candida albicans.
10. Clostridium perfringens.
11. Staphylococcus aureus.
12. Staphylococcus epidermidis.
13. Streptococcus species ( Beta -hemolyticus ).
    1. Positive blood culture for definitive diagnosis is seen in:
       1. Subacute bacterial endocarditis.
       2. Salmonellosis (typhoid fever).
       3. Brucellosis.
       4. chronic meningococcemia.
       5. Gonococcal infection (gonococcemia).
       6. Tularemia.

The person with sepsis may have:

1. Fever and chills.
2. Less frequent urination.
3. Nausea.
4. There may be rapid breathing and tachycardia.
5. Confusion.
6. There may be a drop in blood pressure.
7. There may be a failure of one or more organs.

 

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