Blood cultures - how many sets? how many bottles?

So until last week I thought all microbiologists agreed that we should aspire to 2 sets of blood cultures. I now discover that some people not only think that 2 sets is overkill, they also are happy with just one bottle! There seems some doubt as to whether this should be the aerobic or anaerobic. Anyway, made me look at our data. I’m sure others have done likewise. Be interesting to combine experiences…

 Effect of multiple sets on positivity rate (significant growth only)

 So we now get 2 sets of blood cultures sent from the ED in about 20% of cases. And the second set does not add a huge amount of value.

 90% of positive episodes in which 2 sets were taken were positive in both sets

 Taking a second set of cultures probably increases coliform detection by about 5-10%

 There was little effect on isolation of other significant organisms
Bottle type and positivity

 Looking at all significant culture results, which bottles were positive?

 674 / 1053 significant blood cultures were detected in both bottles

 217 / 1053 were detected in anaerobic only

 162 / 1053 were detected in aerobic only

Conclusions

 Taking more than 1 set may not add much value. But not taking an aerobic and anaerobic bottle - I find it harder to understand that. You will miss important pathogens quite frequently. I would be happy to promote properly filled single sets (aerobic and anaerobic).

 Another metric we could maybe get out of the newer blood culture machines is around bottle fill volumes. Perhaps another thing to base quality improvement around? But if anyone has similar data then perhaps we should combine and make a paper out of this. Particularly given the

Comments

Post a Comment

Popular posts from this blog

Artefactual hyperkalemia - dangerous, expensive. And preventable.

Image
Potassium is part of a renal profile, the most commonly ordered test in pathology.  In N Devon we do just over 100000 primary care tests per year for a population of 160000 Assuming we are similar to others, that would be about 40 million primary care tests per year in the UK. Most potassium in a blood sample sits inside the blood cells, and there is a large concentration gradient across the cell membranes. This is maintained through the the Na/K ATPase, which uses energy to drive sodium out of the cell, in return for potassium entering the cell. Because this is an enzymatic process it is extremely sensitive to environmental conditions. For instance, as temperature rises then the enzyme works faster, pumping more potassium out of the serum into the cell. Conversely, when it is cold the pump doesn't work well and potassium leaks out of the cells. All this means that the level of potassium in the serum can be affected by the conditions in which a non-stabilised sample is kep...
Read more

Use of Peezy device to try to improve quality of urine culture

Image
Background Urine cultures are often contaminated, making interpretation difficult. Pure growths may often not reflect infection and may be due to contamination - in our lab only one third of pure growths from pregnant women are reproducible.  In pre-op urines mixed growths make optimising prophylactic antibiotics difficult. We often end up giving broad spectrum antibiotics to cover all the organisms in a mixture as there is insufficient time to get a repeat. Alternatively, multi-resistant organisms may not be covered adequately. For patients with bacteraemia from a urinary source, many have a mixture in their urine culture. This compromises early rationalisation of antibiotic therapy. The Peezy has been designed to try to improve the quality of urine specimens by automatically discarding the beginning and end of the urine sample. In 2018 we trialled its use in pre-operative patients. These are the results. Number of patients The Peezy was used for both orthopaedic...
Read more

Updated on SoS - Introducing CARIS

Introducing CARMIS - Codes of Antibiotic Responsive Medical Infections associated with Sepsis. In a previous blog I developed the work on SoS codes of Matt Inada-Kim to focus on those codes that are are associated with high mortality infections. Having just completed the first GIRFT deep dive, this concept worked, but was clear it needs development. The first is with the "branding", and we need a new name that more clearly distinguishes this from sepsis, and makes it clear that it is derived from Hospital Episode Statistics. I also felt we needed more categories, to make the reasoning clearer. It is hard to know how to deal with things like aspiration pneumonia and COPD. These have amongst the highest mortalities of any common disease, but it is debatable how much antibiotics contribute to management. Similarly, surgical conditions that are principally managed through intervention (certainly perforation, but also probably cholangitis) muddy the waters. My latest feeling is...
Read more