1. Eleanor Bates, Colette McCambridge, Bob Philips, Jonathan Sandoe
Optimising Paediatric Blood Cultures – Are We Inoculating Enough Blood?
Eleanor Bates, Colette McCambridge, Bob Philips, Jonathan Sandoe
Figure 1: Proportion of paediatric blood cultures in Leeds Children’s Hospital adhering to trust guidelines. Only 34% of returned bottles contained the recommended volume of blood
Background
Bloodstream infections are an important cause of morbidity and mortality in children. – sepsis is leading cause of death in under 5s worldwide.
Presentation is non-specific, and rapid deterioration can occur - prompt recognition is vital.
Blood cultures are the recommended gold standard investigation (NICE)
A positive blood culture enables targeted antibiotic therapy.
A negative blood culture can enable cessation of empirical antimicrobials.
The volume of blood sampled in a culture is proportional to its yield/positivity – the probability of detecting a pathogen increases with the volume of blood obtained.1,2
Insufficient blood can result in false negatives and delayed or missed diagnoses, the need for repeat cultures, inappropriate treatment, prolonged hospitalisation and therefore increased patient morbidity and costs to the NHS.
Discussion
A positive blood culture is considered diagnostic for bacteraemia whilst a negative blood culture also influences the management of a patient, therefore it is vital to get the test as sensitive and specific as possible
Over half of blood cultures bottles returned were under filled, with only 34% adhering to guidelines. Though improvement from a previous audit is noted, further intervention is necessary to ensure more cultures contain a sufficient volume, ensuring the optimum diagnosis of paediatric blood stream infections
51% of blood cultures contained less than 1ml of blood, and 28% contained less than 0.5ml of blood. It is known that blood volumes of under 0.5ml decreases the sensitivity and therefore the reliability of under filled blood culture bottles is questionable3,4.
The lack of blood inoculated could be due to lack of awareness from staff about the importance of blood volume or due to the difficulties that can be faced when obtaining blood from a child. This problem is likely to be reflected in other hospitals across the country.
Limitations of this study include not stratifying the data by age or weight and being reliant on blood sciences laboratory staff members to weight the blood bottles on return to the laboratory.
The optimum volume of blood to inoculate in paediatric blood cultures is yet to be established and may involve calculating an ideal volume by weight of the child5. More research is required in this area as blood cultures results influence antibiotic treatment regimens.
Results
700 bottles were weighed and distributed.
A total of 490 blood culture bottles were returned to the laboratory. 18 were excluded from data analysis, 17 due to a negative blood volume and 1 as an outlier.
The median blood volume inoculated was 0.95ml, range 8.68ml.
242 bottles contained less than 1ml of blood (51%)
160 blood culture bottles contained an adequate volume of 1-3ml of blood (34%)
71 bottles had more than 3ml of blood inoculated (15%)
Methods
Study design: Clinical audit.
Paediatric blood culture bottle stock within Leeds General Infirmary (LGI) was intercepted.
Bottles were weighed by researchers over a 3 month period (Nov 2016 – Jan 2017) using calibrated scales sensitive to 0.01g, and labelled with a pink sticker.
Weight and sequence barcode were recorded in a table.
Weighed and labeled bottles were placed back into circulation to be used as per normal protocol.
Staff working in the LGI Blood Sciences Laboratory were asked to re-weigh inoculated samples on their return to the lab, and record this in the table. (Dec 2016 – April 2017).
Figure 2: Frequency distribution graph of volume of blood inoculated. Guidelines for paediatric blood cultures state the volume of blood should be between 1-3ml of blood, indicated by the blue lines. The highest volume frequencies were all below 1ml of blood, the minimum recommended value.
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. 2007:119(5); Nice. Management of a feverish child. Available from: (accessed October 2017) 3 Schelonka RL, Chai MK, Yoder BA, Hensley D, Brockett RM, Ascher DP. Volume of blood required to detect common neonatal pathogens. The Journal of pediatrics. 1996;129(2): Kellogg JA, Manzella JP, Bankert DA. Frequency of Low-Level Bacteremia in Children from Birth to Fifteen Years of Age. Journal of Clinical Microbiology. 2000;38(6): Dien Bard J, McElvania TeKippe E. Diagnosis of Bloodstream Infections in Children. Journal of Clinical Microbiology. 2016;54(6):
Clinical Bottom Line
Over half of pediatric blood culture bottles audited were under filled within Leeds Children’s Hospital.
The minimal recommended volume is 1-3ml, but there had been an improvement from a previous audit.
More work is needed to emphasise the importance of volume and change behaviours.