The article by Connell et al (1) on volume of blood submitted for
culture is very pertinent. It is well established that higher the volume
of sample taken in a culture bottle, higher is the yield. Schelonka et al
(2) had shown that 1 – 2 milliliters of blood is needed for microorganism
recovery in the face of low-colony-count sepsis. Isaacman and his
colleagues (3) had also proved that pathogen recovery rate in the same
sample was higher in a larger volume aliquot than that for a smaller
volume samples.
In a sick baby, though we have other surrogate markers of infection
such as CRP, we still depend upon a positive blood culture for a
definitive diagnosis and subsequent therapeutic decisions.
Though Connell’s work has once again showed the need for adequate
sample volume, we are concerned that it spite of an educational
intervention, the percentage of samples with an adequate volume only
increased from 46% to 63.9%. One would have expected that during the time
of an active training programme, the number of adequately taken samples
should have been much higher.
But perhaps this is a reflection of the ground realities on a busy
neonatal or paediatric ward. The residents who would be taking the blood
samples know that should they take an inadequate sample for biochemical or
haematological workup, it would not be processed and they would have to
retake another sample. However, with blood culture samples no such
immediate feedback is available and hence if only a limited sample is
obtained on venepuncture, quite possible only the least amount would make
its way in a culture bottle.
With a number of studies proving the crucial importance of obtaining
an adequate blood culture volume, we feel that the time has come to
develop a method of rejecting inadequately filled culture bottles. As
blood culture systems are nowadays almost fully automated, it should be
possible to develop a system of automatic weighing of filled culture
bottles and immediate feedback regarding inadequate samples. This would be
the only way of ensuring that adequate samples are taken in culture
bottles each and every time and we would not have any more instances of
missed diagnoses.
References
1 Connell TG, Rele M, Cowley D, Buttery JP, Curtis N. How reliable is
a negative blood culture result? Volume of blood submitted for culture in
routine practice in a children's hospital. Pediatrics. 2007 May;119(5):891
-6.
2 Schelonka RL, Chai MK, Yoder BA, Hensley D, Brockett RM, Ascher DP.
Volume of blood required to detect common neonatal pathogens. J Pediatr.
1996 Aug;129(2):275-8
3 Isaacman DJ, Karasic RB, Reynolds EA, Kost SI. Effect of number of
blood cultures and volume of blood on detection of bacteremia in children.
J Pediatr. 1996 Feb;128(2):190-5.
Conflict of Interest:
None declared
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