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Published: September 2011Print Record of Viewing
Dr. Brad Karon discusses the most effective way to reduce blood culture contamination.
Presenter: Brad Karon, MD, PhD
Welcome to Mayo Medical Laboratories' Hot Topics. These presentations provide short discussions of current topics and may be helpful to you in your practice.
Our presenter for this program is Dr. Brad Karon, Assistant Professor of Laboratory Medicine and Pathology, and Medical Director of Laboratory Services in the Division of Clinical Core Laboratory Services at Mayo Clinic in Rochester, Minnesota. Dr. Karon will discuss the most effective way to reduce blood culture contamination. Thank you, Dr. Karon.
Thank you, Sharon. For the past few years, I have given case-based presentations at our annual Mayo Clinic Phlebotomy conference and called these presentations “Phlebotomy Top Gun”. During the conference attendees are presented with a phlebotomy related situation or problem and asked to decide on the best course of action. I then present evidence and/or data related to each case and attendees then vote again on the best course of action at the end of each case. What follows today is one case from a previous phlebotomy conference.
Here’s a question from a previous phlebotomy conference presentation.
Nurses currently draw blood cultures in our ED using alcohol and iodine disinfection. The most effective way to reduce blood culture contamination would be to:
At the conference attendees would now have a chance to use an audio response system to select what they believe to be the best answer. The percent of attendees selecting each answer would be displayed before I move on to the data or evidence surrounding this question.
The use of chlorhexidine versus iodine for blood culture disinfection is something I refer to as the epic battle because of the number of studies that have been done and generally with differing conclusions which has led to very strong opinions about this matter. Studies differ in the exact preparation of chlorhexidine and iodine used, the health care providers who collected the blood cultures, the base line overall contamination rates and other variables that make direct comparisons between the studies somewhat difficult.
This is an example of one relatively recent study that compared a 2% chlorhexidine solution to an aqueous iodine preparation. It was a large prospective trial and for that reason is considered to be one of the better studies. However note that baseline blood culture contamination rates at this institution where the study was performed were quite high, over 5%, which might have impacted the end results. The study was conducted in two different patient care environments – Medicine and ICU wards where medical students and residents were responsible for blood culture collections, and the Emergency Department where nurses were responsible for collecting blood cultures.
The overall contamination rate was much higher in the Emergency Department, 8.3%, compared to the Medicine and ICU wards at 3.3%. Within the medicine and ICU wards, where baseline contamination was lower, chlorhexidine provided a slight but statistically significant benefit compared to aqueous iodine. Within the Emergency Department, where overall contamination rate was quite high, chlorhexidine showed a very large effect in reducing blood culture contamination rate. Thus the impact of chlorhexidine on lowering blood culture contamination rates was dependent upon the patient care environment, very likely due to differing base line contamination rates in the different patient care environments.
This is another smaller prospective trial that’s a little bit older from 2002. In this study a 2% chlorhexidine solution similar to the first study I just discussed was compared to a 2% alcoholic tincture of iodine so the difference here is an aqueous versus an alcoholic preparation of iodine and we will talk about that in a little bit. In this study, medical students, house officers (or residents and fellows) and health care technicians drew cultures. The overall contamination rate at this institution was quite a bit lower .5% actually 10 fold lower than the first study I just discussed. And in the end they found no significant difference statistically between chlorhexidine and iodine in terms of contamination rate of blood cultures. So here again, the major difference is a alcoholic versus a aqueous preparation of iodine and a very much lower baseline contamination rate such that there was no difference between chlorhexidine and the alcoholic iodine preparation.
Finally a third study I will discuss in this epic battle between chlorhexidine and iodine was done in 2004 and in this study again they studied a 2% chlorhexidine solution versus an iodine tincture. It was a before and after study, so again, they were not prospectively studying it. They switched from iodine to chlorhexidine and studied contamination rates before and after. Blood culture collection was done by a combination of dedicated phlebotomists (about 1/3 of the cultures), nurses and emergency department staff. Similar to the last study I just discussed, there was no statistically significant difference in the rates of blood culture contamination between the period where they used chlorhexidine and the period where they used a tincture of iodine.
And then the final study I will discuss in this issue of chlorhexidine versus iodine disinfection for blood cultures is a review of all prospective studies done between 1996 and 2006. So this was a sort of a systematic review pulling out data from individual studies trying to come to an overall conclusion. The conclusion of this systematic review was that there was no clear advantage of chlorhexidine over a alcoholic tincture of iodine. They did conclude based on the data out there from all prospective published studies that both chlorhexidine and the alcoholic tincture of iodine may be better than the aqueous povidone-iodine solutions. And they did specifically caution that actually that first study I discussed, the very largest study, did compare chlorhexidine to an aqueous iodine preparation. The author suggested they needed to keep that in mind before concluding that chlorhexidine was better than all iodine solutions. The systematic review also concluded, based on the available evidence, that pre-packaged skin preparations whether they be chlorhexidine or iodine were better than taking a gauze pad and soaking it with a bottle or an iodine solution. And I think most of us now do use some sort of pre-packaged skin prep but if you’re not, you should be aware that that was a conclusion of this systematic review.
So what about which staff collects the blood cultures? Wouldn’t it be nice to know if there’s any objective data out there that shows if you have dedicated staff, in general, that would be dedicated phlebotomy staff, to collect blood cultures that that does improve the contamination rate or result in some benefit. As I noted through the three studies I discussed, in general, contamination rates seem to be lower where you had phlebotomists collecting as opposed to residents and medical students and emergency department where nurses tend to collect or ED staff tend to collect tended to have the highest contamination rates. But has anyone specifically looked at not changing patient care areas but let’s stay just staying within the Emergency Department comparing contamination rates when phlebotomists versus non-lab personnel collect blood cultures.
Well, in fact, this study was done. It was done in 2008 led by Corinne Fantz at Emory University and her colleagues in Laboratory Medicine and nursing there. And it was a prospective observational study. It compared blood culture contamination rates between various times and shifts in the Emergency Department. It turns out that they had certain times and shifts where they had dedicated laboratory phlebotomists collecting blood cultures and other times where non lab staff, and that would include nurses, residents, attending physicians, collecting blood cultures. Unfortunately, this study does not specify what type of disinfection they use whether is was chlorhexidine, iodine or something else. But they were able to directly compare rates of contamination of blood cultures between times in the ED when lab staff or phlebotomists were collecting the cultures to non-lab staff. Blood culture contamination rate was drastically lower, 1.1%, during the times when phlebotomists were collecting blood cultures versus 5%, about five fold higher, in the times or shifts when non-lab staff and again this was all within the same Emergency Department so we don’t have the issues of different patient care areas in this study. They also went on to look at what were the cost avoidance because admitting a person with a falsely positive blood culture is expensive in terms of hospital stay and treatment. They estimated a cost avoidance of almost a half million dollars if there were laboratory personnel or phlebotomists collecting blood cultures all the time. And that would more than pay for the cost of having those phlebotomists present.
So the summary on chlorhexidine versus iodine, what I call the epic battle, is that both chlorhexidine and tincture alcoholic preparations of iodine can be effective disinfectants for blood culture collection. Obviously, as you all who are involved in phlebotomy on a daily basis know, technique is probably more important than what product you use and technique, training and following procedures. Many institutions, and that includes ours at Mayo Clinic are able to keep or reduce contamination rates below 2 or even below 1% with a tincture of iodine product if they have dedicated trained staff collecting blood cultures. And finally, in terms of which one to choose, chlorhexidine or an iodine product, both products have their own set of advantages. Chlorhexidine is prepackaged, perhaps a little bit faster and less messy than iodine tinctures, and it is widely used and recommended now for central line disinfection and so it’s available and nursing and other staff are probably familiar and have it available to use, so chlorhexidine has those advantages. Iodine can be cheaper depending on the type of preparation and packaging. It has no age restrictions in terms of the very young patients and it can perhaps be more effective but again I think overall the data doesn’t suggest one product as necessarily better than the other.
So now we come back to our original question and in the Phlebotomy conference I would re-present this question so.
Nurses currently draw blood culture collections in our ED using alcohol and iodine disinfection. The most effective way to reduce blood culture contamination would be to:
During the conference all attendees would now vote again on the same question and we would be able to compare live at the conference whether the opinions of the audience had changed from before I presented the evidence and data to after. And then finally I would present based on my review of this data evidence what I feel to be the best answer and in this case that would be 4. The objective data and our experience would suggest that the most effective way in this situation to reduce blood culture contamination rates would be to provide dedicated phlebotomy staff to collect blood cultures in the ED.
Finally, I want to wrap up by letting you all know that we will once again this year be having our Phlebotomy conference. This year’s conference is titled "Phlebotomy 2011: Innovations in Quality, Service and Patient Care." The conference will be held at the Kahler Grand Hotel here attached to the Mayo Clinic in Rochester on October 6th and 7th 2011. For more information please refer to the Mayo Medical Laboratories.com web site for both registration information and more detailed information about our program and plans for this year.