Exposing the consequences of blood culture contamination.

Cry Wolf explains the consequences of taking shortcuts with blood culture collection.

Just like the boy who cried wolf, high numbers of false positive results cause physicians to question the test, compromising a fast and appropriate response.

Expert clinicians highlight the high cost of false positive blood cultures for both patients and hospitals and share a consensus that caregiver compliance with best practices can reduce false positives blood cultures.

Read the Transcript

I certainly became aware of false positives when I was a fellow going through training. Recognizing how every time we were distracted with a false positive, it took away from patients who were truly sick. If there’s a false positive blood culture, that means the patient is subject to potentially unnecessary antibiotic therapy, additional testing that may be unnecessary to figure out where the infection’s coming from rather than focusing on why the patients truly sick and trying to get them better and out the door.

When I was a staff nurse in the emergency department, I really had no awareness of blood culture issues. We drew them and we went on with our day. It was another task that we checked off. It wasn’t until I became an educator that I became aware that, oh, this is a big issue with big consequences.

I never realized that false positives were driving poor patient flow. They’re driving costs up. It’s almost like false positives are this silent vine that just takes over, but nobody really sees it because we’re focused on other things and it’s a huge, huge part of what we have to do every day to lower costs and to lower length of stay.

We realize that we are potentially treating patients who don’t even have a real infection. We’re exposing them to unnecessary antibiotics, increased length of stay and all the complications that go along with that. As our individual organizations have an increasing focus on antimicrobial stewardship and we realized that there are not insignificant quantities of antibiotics used to treat infections that aren’t actually infections and they’re false positives.

A contamination can take a treatment plan in a completely different direction than what the patient actually needs and it disguises a lot of the things that we should be paying attention to.

Some of the dangers patients face when they’re in the hospital for longer than they need to be include, not only C Diff., but MRSA infections, skin breakdown, pulmonary embolism, DVTs. Everything that you get from not moving around and just being in the hospital. You know, just being in the environment itself puts you at risk.

There are articles out there that had been written as early as 1990 about what it’s costing your organization to continue to have these really high contamination rates.

We’re moving toward a world where hospital-acquired infections will not be covered under most insurance plans, and so if a patient develops C Diff. disease during the hospital stay, as a result of unnecessary antibody therapy, then any measures that are taken to treat the patient for that C Diff. infection may not be covered by insurance and so the hospital wouldn’t get reimbursed for that care.

The cost associated with some of these contaminations and some of these extra lengths of stays really falls on the hospital itself, for the most part. If it costs you more to take care of that patient, that’s less reimbursement the hospital will get from that stay. The more complications, the less money that certain payers are providing to the hospital, kind of the pay-for-performance measures.

I think that if emergency nurses really understood all the consequences, compliance would not be an issue.

When educating nurses, especially in the emergency department, they have to see the relevance. If we don’t understand the why, we may take shortcuts that we shouldn’t take. I think the key to the sustainability is accountability. Our Lab has signs that they put up this say, my results are only as good as the specimen you send me, and we weren’t sending them good specimens. We were sending them contaminated specimens and so the results weren’t good. If they understand why they need to do it a certain way and do it well, the consequences downstream, then they’ll do it right.

But what really drives it home is when you tell them why you need to do it this way and I find we get a lot more compliance that way. You tell them why. The nurses always want to know why. It’s about making it part of your culture. It is a culture of safety, a culture of doing what’s right for the patient.

From a patient perspective, I guess I try to think about my mother who is in her seventies and what would this mean to her? You know, every false positive is a story. It’s a person that we’re effecting.

Essentially it comes down to is the patient getting the quality care that they deserve and that they’re seeking. And are we doing everything we can to make sure that they get that. And having those low contamination rates is one of those ways.

Test Your Blood Culture Collection IQ

This essential resource for nurses and phlebotomists explains the importance of blood culture testing and its current shortcomings associated with culture contamination.

The video walks the viewer through the established best practice for blood culture collection and identifies the common points of contamination.

Lastly, the viewer is introduced to a collection technique with Flash Technology, which sidelines the initial flash of blood and skin contaminants therein.

Read the Transcript

When a patient shows signs of a bloodstream infection, a physician will likely order a blood culture test.

A blood sample is collected in two special bottles—one that fosters the growth of aerobic microbes and the other anaerobic microbes.

Any microorganisms present in the sample will grow and return a POSITIVE test result, which may inform a diagnosis and triggers antibiotic therapy.

However, the clinical value of blood culture testing may be compromised by improper collection technique.

For example, if not enough blood is collected, a False-Negative may occur allowing the infection to go undiagnosed and antibiotics to be held or discontinued putting the patient at higher risk of sepsis.

Likewise, a positive blood culture result may not indicate a bloodstream infection at all but rather a false-positive due to specimen contamination.

Contaminants can come from

  • patient skin
  • clinician hands
  • blood culture bottle tops
  • attachment or detachment of transfer components
  • and existing intravenous line

In fact, approximately 30% of the patients who test positive do NOT have a bloodstream infection.

Hospitals absorb the cost of additional staff time, testing, treatment, and extended stays. Just one contaminated culture can add 2-4 days and between $4000 and $10,000 in costs. But, if the patient develops a hospital acquired condition during the extended stay, the cost could be much higher.

Guessing wrong can have terrible consequences.

A patient may experience unnecessary stress, longer hospital stays, exposure to unneeded antibiotics, and adverse events.

Fortunately, the accuracy of blood culture testing can be improved by following collection best practice.

Best practice blood culture collection requires the following per each set:

  • Gloves
  • Skin antiseptic
  • Tourniquet
  • Fully-assembled closed-system butterfly collection set
  • 2 culture bottles – one aerobic and one anaerobic

Two sets of cultures should be taken from two different venipuncture sites.

Although it may seem unkind to stick the patient twice, it is important.

Positive culture results from both sites will likely indicate a true bloodstream infection.

But, if only one culture grows an organism, the physician may suspect a contaminant.

To begin, skin and bottle preparation reduces potential points of contamination.

First, disinfect the tops of culture bottles per hospital policy.

Next, apply a tourniquet and locate the patient’s vein.

Proper skin antisepsis is critical because the most common contaminants are microbes from the patient’s own skin.

  • Wash hands and wear clean gloves.
  • Prep the venipuncture site according to hospital policy
  • Do not re-palpate the vein once prepped.

Then, perform the venipuncture using a closed-system butterfly collection set with a bottle holder.

Some patients have veins that are difficult to access and could collapse under the vacuum pressure of a vacutainer culture bottle.

Clinicians avoid this by using a syringe to control the pressure.

However, this requires the clinician to “open” the system to transfer the sample to the bottle adding steps and significantly increasing the risk of contamination.

Another open system technique is obtaining the sample from a freshly placed IV – a practice that also carries higher risk of contamination.

No matter which method is used, fill the aerobic bottle first, then the anaerobic bottle, making sure to fill the bottles to the optimum volumes required per hospital policy to help ensure accurate results.

Collect any additional lab vials AFTER completing the blood culture set.

After collection, withdraw the butterfly, activating the needle’s safety mechanism.

Following hospital policy, dress the venipuncture site, dispose of the collection set, and then label, document, and send the specimens to the lab.

Now that we have covered the best practice basics, here’s a little test.

True or False: With best practice compliance, contaminated blood cultures will disappear.


Unfortunately, skin antisepsis does not eliminate contamination from skin microbes.

As many as 20% of skin microbes are unaffected by antisepsis.

During venipuncture the needle traps a minute core of dermis and if microbes are present, they are given a straight line into the culture bottle.

A blood culture collection set that uses passive flash technology sends the initial flow of blood—and contaminants therein—into a “U” shaped side channel.

When the collection bottle is attached, the specimen flows from the vein to the bottle in a closed system through the sampling channel into the bottle.

When necessary, flash technology can be used with a syringe or used to draw blood from a fresh IV.

Clinical studies have shown that use of a flash technology can reduce contaminated blood cultures by more than 80%.

Blood culture collection best practice compliance combined with passive closed-system flash technology can dramatically improve the clinical value of blood culture testing, leading to more effective and lower cost treatment of patients.

It is Time to Challenge the 3% Benchmark

Since Spring 2020, the CMS Conditions of Participation have focused on hospital efforts to reduce the development and transmission of HAIs and antibiotic-resistant organisms.

CMS requires hospitals to “demonstrate adherence to nationally recognized best practices for improving antibiotic use with “active and hospital-wide” stewardship programs.

Antibiotic stewardship begins with correctly identifying patients in need of treatment. 

A 3% blood culture contamination rate results in US hospitals treating more than 1 Million Americans each year for non-existent infections with unnecessary antibiotics. This high rate of false positive results will no longer be compliant with the intention of the CMS rule.

Learn more about CMS requirements and how the 3% benchmark misses the mark.

Have you experienced a false positive blood culture?

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What is best practice for blood culture collection?

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What are the causes/impacts of contamination?

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Who is working to improve blood culture testing?

See the leaders.

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