Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Refining the use of blood cultures

Oldberg, Karl LU orcid (2026) In Lund University, Faculty of Medicine Doctoral Dissertation Series
Abstract
This thesis is built upon four research projects, in which we investigated different aspects of increasing the diagnostic yield of blood cultures. Blood culture sampling using a single venipuncture (single-sampling strategy, SSS) is non-inferior to sampling from two separate venipunctures when sensitivity is considered. The effect of SSS on blood culture contamination rate is less known. In Study I, we retrospectively evaluated the effect of introducing SSS and initial sample diversion in our region. The proportion of sampling events in which the recommended 4 bottles were collected, increased after the intervention, and sensitivity remained unchanged. There was a decrease in the proportion of sampling events in which coagulase-negative... (More)
This thesis is built upon four research projects, in which we investigated different aspects of increasing the diagnostic yield of blood cultures. Blood culture sampling using a single venipuncture (single-sampling strategy, SSS) is non-inferior to sampling from two separate venipunctures when sensitivity is considered. The effect of SSS on blood culture contamination rate is less known. In Study I, we retrospectively evaluated the effect of introducing SSS and initial sample diversion in our region. The proportion of sampling events in which the recommended 4 bottles were collected, increased after the intervention, and sensitivity remained unchanged. There was a decrease in the proportion of sampling events in which coagulase-negative staphylococci grew in 1-2 out of 4 bottles, but an increase in the proportion of sampling events in which they grew in >2 bottles. This may indicate an increase in contaminations of multiple bottles, which can be hard for clinicians to identify.

Study II and III investigated whether persistent bacteraemia or blood culture time to positivity (TTP) were useful in the diagnosis of infective endocarditis caused by Enterococcus faecalis. Study II prospectively included patients with E. faecalis bacteraemia for repeated blood culture collection. Persistent growth in repeated cultures was associated with a high probability of infective endocarditis or other infectious foci that needed special therapeutic consideration. However, most patients with such complicated infections did not have persistent bacteraemia, which limits the use of repeated blood cultures. In study III, a retrospective observational study, we found that the median TTP among patients with infective endocarditis was shorter than in patients with other foci of infection. There was no difference in TTP between patients who died within 30 days and those who survived.

A major problem with using TTP is that it is shortened when the time elapsed from sampling to incubation start (TTI) increases. This makes comparisons between studies difficult and obscures the association between TTP and outcomes of interest. In Study IV, we used a large retrospective dataset to develop a method for correction of TTP for TTI, based on the linear correlation between these variables. Corrected TTP was more strongly associated with 7-day mortality than crude TTP.
(Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Lamy, Brigitte, Université Paris Sorbonne Nord, Paris, France
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Blood culture, bacteraemia, Infective endocarditis, Time to positivity, Persistent bacteremia
in
Lund University, Faculty of Medicine Doctoral Dissertation Series
issue
2026:64
pages
105 pages
publisher
Lund University, Faculty of Medicine
defense location
Segerfalksalen, BMC A10, Sölvegatan 17 i Lund. Join by Zoom: https://lu-se.zoom.us/j/66304354729?pwd=sAjgmtyr83FjVPwzS491JOeOnP9qqa.1
defense date
2026-05-08 09:00:00
ISSN
1652-8220
ISBN
978-91-8021-862-7
language
English
LU publication?
yes
id
386e43c5-491d-479f-9302-85c5344df435
date added to LUP
2026-03-20 18:02:06
date last changed
2026-04-16 12:33:57
@phdthesis{386e43c5-491d-479f-9302-85c5344df435,
  abstract     = {{This thesis is built upon four research projects, in which we investigated different aspects of increasing the diagnostic yield of blood cultures. Blood culture sampling using a single venipuncture (single-sampling strategy, SSS) is non-inferior to sampling from two separate venipunctures when sensitivity is considered. The effect of SSS on blood culture contamination rate is less known. In Study I, we retrospectively evaluated the effect of introducing SSS and initial sample diversion in our region. The proportion of sampling events in which the recommended 4 bottles were collected, increased after the intervention, and sensitivity remained unchanged. There was a decrease in the proportion of sampling events in which coagulase-negative staphylococci grew in 1-2 out of 4 bottles, but an increase in the proportion of sampling events in which they grew in &gt;2 bottles. This may indicate an increase in contaminations of multiple bottles, which can be hard for clinicians to identify. <br/><br/>Study II and III investigated whether persistent bacteraemia or blood culture time to positivity (TTP) were useful in the diagnosis of infective endocarditis caused by Enterococcus faecalis. Study II prospectively included patients with E. faecalis bacteraemia for repeated blood culture collection. Persistent growth in repeated cultures was associated with a high probability of infective endocarditis or other infectious foci that needed special therapeutic consideration. However, most patients with such complicated infections did not have persistent bacteraemia, which limits the use of repeated blood cultures. In study III, a retrospective observational study, we found that the median TTP among patients with infective endocarditis was shorter than in patients with other foci of infection. There was no difference in TTP between patients who died within 30 days and those who survived.<br/><br/>A major problem with using TTP is that it is shortened when the time elapsed from sampling to incubation start (TTI) increases. This makes comparisons between studies difficult and obscures the association between TTP and outcomes of interest. In Study IV, we used a large retrospective dataset to develop a method for correction of TTP for TTI, based on the linear correlation between these variables. Corrected TTP was more strongly associated with 7-day mortality than crude TTP.<br/>}},
  author       = {{Oldberg, Karl}},
  isbn         = {{978-91-8021-862-7}},
  issn         = {{1652-8220}},
  keywords     = {{Blood culture; bacteraemia; Infective endocarditis; Time to positivity; Persistent bacteremia}},
  language     = {{eng}},
  number       = {{2026:64}},
  publisher    = {{Lund University, Faculty of Medicine}},
  school       = {{Lund University}},
  series       = {{Lund University, Faculty of Medicine Doctoral Dissertation Series}},
  title        = {{Refining the use of blood cultures}},
  url          = {{https://lup.lub.lu.se/search/files/247613365/Refining_the_use_of_blood_cultures_e-spik.pdf}},
  year         = {{2026}},
}