Bld Cx's: does sample size affect result?

[NICU_Nurse, BSN, RN]

Okay, another debate-buster for you guys.

I've tried calling Micro but can't get anyone on the phone!

For infants needing bld cx's, we use BD pink-label bottles. Per lab, these require a minimum of 0.5cc-1.0cc of blood, up to a max (per design) of 3cc (before requiring a different-colored label/tube).

One of our RT's is claiming to have sent as little as 0.2cc of blood in these tubes and claims "No one ever said anything." My argument was that the bottles may have been designed with a certain amount of medium, and sending an insuffecient sample may mean that the smaller blood sample is too diluted (the proportion of medium:blood would be off) to develop properly.

He stated that if it's "gonna grow, it's gonna grow."

What do you all think?

[Gompers, BSN, RN]

Okay, another debate-buster for you guys.

I've tried calling Micro but can't get anyone on the phone!

For infants needing bld cx's, we use BD pink-label bottles. Per lab, these require a minimum of 0.5cc-1.0cc of blood, up to a max (per design) of 3cc (before requiring a different-colored label/tube).

One of our RT's is claiming to have sent as little as 0.2cc of blood in these tubes and claims "No one ever said anything." My argument was that the bottles may have been designed with a certain amount of medium, and sending an insuffecient sample may mean that the smaller blood sample is too diluted (the proportion of medium:blood would be off) to develop properly.

He stated that if it's "gonna grow, it's gonna grow."

What do you all think?

I don't have the reference, but I am sure that I read an article that stated that samples with less than 1cc of blood are more likely to come back with a false negative result. We use the bottles with like 10 cc of this black fluid in them, so there is no way for the lab to know how much blood we added - thus they CAN'T "say anything" about it. They trust that we added adequate blood, and it is our responsibility to our patients to do so as well. If for some reason the most blood you can get is 0.5cc, I would send that, but if at all possible, a 1cc sample is best.

[dawngloves, BSN, RN]

I've wondered that too. I've sent cx to the lab with less than the 1cc they ask for, maybe .5 or so, and sometimes something grows or it doesn't. I've figured the same. If there's something in there, something will grow.

[Humbled_Nurse]

It should be a minimum of 0.5 cc, but at least 1 cc is ideal. You are much more likely to miss a positive blood culture with 0.5cc or less. That is why physicians may order more than one blood culture from multiple sites at one time because the chances of yielding a positive is much greater so if the culture comes back negative then they can pretty confident that is a true negative.