I have a two part question.
Why when it comes to bacteriological testing for a clinical sample, here blood, it is crucial to get the adequate volume of blood from the patient and not a smaller amount? Why is it important?
And why when it comes to infants and children, a smaller volume of blood is required for a bacteriological test than for a adult? (But other than it's a small baby or infant and we can't take lots of blood.)
Thank you.
Since bacterial load in blood could be small numbers in relation to large volume of blood. Also, the blood is rich with Antimicrobial factors like phagocytes, Antibodies and antibiotics. So you increase the volume of sample to increase the chance of isolating the pathogen.
In regard to infants and neonates, the blood volume is much less and the immune system is still naiive, thus concentration of bacteria is much higher in this case and easier to obtain from smaller volumes.
Hello Twana Omer
The basic recommendation that blood draw for blood culture should be based on the patient's age and/or weight, both of which are interdependent variables.
Part I
Blood culture volume is the most important variable in detecting bacteremia and fungemia as it is directly proportional to recovery rate. Obtaining an adequate blood volume is important for the detection of bloodstream infections. There is a 3% increase in sensitivity for every extra mL collected. Increase in the volume of blood collected, will result in a further increase in positivity rates.
Sometimes, a false-negative result may be obtained because of the inhibitory effect of complement, lysozyme, phagocytes, antibodies, and antimicrobial agents. This problem may be solved by using neutralizing agents such as resin-containing culture media, which will inactivate the inhibitory substances present in blood.
Please refer to the article attached below.
Article Evaluation of the blood volume effect on the diagnosis of ba...
Part II
The procedure for blood sampling in paediatric patients, particularly the optimal blood volume, is the subject of controversy stemming from a lack of knowledge of the bacterial load and because of several obstacles such as low intravascular volume and the risk of causing anaemia.
Most studies suggest a blood volume of 0.5–1 mL for neonates. The volume of 0.5 mL was most probably chosen as this is the minimal volume validated by the companies offering blood culture diagnostics.
For infants (≤12 months, equating to 10 years, >31.2 kg) a blood volume of at least 20 mL are recommended.
Please refer to the article attached below.
Article The correct blood volume for pediatric blood cultures: a conundrum?
Age-dependent approach can increase the positivity of blood cultures as compared to an insufficient blood volume.
Best.
Actualy, the success of bacteriological study of blood directly depend on size volume of sample. But, you should follow strategy minimize side risk for patient and minimize risk VME (very major error - report the negative result when bacteriemia is present). So, you the volume of blood sample are depend on CBV (circulation blood volume). May be it review will useful for you: Article A Comprehensive Update on the Problem of Blood Culture Conta...
According to studies, this is due to the bacterial yield as the sample size increases such as for every 1 ml of blood. However, pediatric patients may suffer from anemia from extracting too much.
https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(19)30533-6/pdf
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