Smallest gauge for blood draw?

  1. Hi there,

    I'm not a nurse, but a vet tech. I need to practice my venipuncture technique and was wondering about whether an insulin needle could be used? Or would the gauge need to be larger due to the viscosity of blood?

    Thanks for any advice, my potential guinea pigs will appreciate it!!
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  2. 21 Comments

  3. by   nursej22
    I would check with your lab. Usually the gauge needs to be big enough to prevent lysing the red blood cells. I think a 20 is about as small as you can go for a human.

    I am not sure you would get much of a flash with an insulin needle, and it may clot rather quickly.
  4. by   Coffee Nurse
    We use 24s in neonates.
  5. by   Euro_Sepsis
    It's a combination of the needle (or catheter) gauge and whatever is pulling the pressure. A good flowing 24g IV and 3ml syringe yields perfectly acceptable results for my peds patients. Directly transferring into the vacutainer tube (using its own pressure) is also a good way to avoid lysis.
  6. by   KelRN215
    Quote from nursej22
    I would check with your lab. Usually the gauge needs to be big enough to prevent lysing the red blood cells. I think a 20 is about as small as you can go for a human.

    I am not sure you would get much of a flash with an insulin needle, and it may clot rather quickly.
    We definitely draw blood from 24 g IVs when placed or 25 g butterfly needles in pediatrics. You can't use a 20 g on a baby.

    I agree that an insulin needle is not appropriate for a blood draw, it's meant for a subq injection.
  7. by   meanmaryjean
    We used 24/25 in PICU.
  8. by   Racer15
    I used 25g needles on rats when I was a vet tech. I also ran all of my own labs so I had to get it right the first time or create more work for myself. An insulin needle is not appropriate for blood draws and I would advise practicing with the biggest gauge you can. That way if you have to go smaller it's not a problem. Why not consult the vet you work for?
  9. by   KLouHerout
    Thanks everyone!!

    I guess I could have clarified. I used to be a vet tech and I'm applying for my dream job at a clinic and really need to practice my technique.

    I appreciate the advice!
  10. by   hherrn
    Quote from Coffee Nurse
    We use 24s in neonates.
    I wish everybody would understand this concept.
    "well, I was taught you need at least a 20g to administer blood". Aaargh. I usualy ask how they would give blood to a baby,
  11. by   Coffee Nurse
    Quote from hherrn
    I wish everybody would understand this concept.
    "well, I was taught you need at least a 20g to administer blood". Aaargh. I usualy ask how they would give blood to a baby,
    To be fair, I doubt adult volumes would run through a 24g.
  12. by   hherrn
    Quote from Coffee Nurse
    To be fair, I doubt adult volumes would run through a 24g.
    I don't thing that the volume is the issue- I think it is the rate. No question a 24 can be used for a transfusion- but I would like to see an authoritative source regarding the rate.
  13. by   Coffee Nurse
    Quote from hherrn
    I don't thing that the volume is the issue- I think it is the rate. No question a 24 can be used for a transfusion- but I would like to see an authoritative source regarding the rate.
    Well, yes. I meant an adult volume of blood in the time blood requires, which would by necessity be a high rate.
  14. by   adventure_rn
    Hmmm, this pediatric gauge size has really gotten me thinking....

    Perhaps it depends on how much pressure you are using to withdraw the blood. For instance, we use 25g (or even 27g) needles in neonates, however we never attach them to vacutainers, but rather draw back slowly with a syringe (then squirt the sample into the vacutainer).

    If you were to stick an adult with a 27 gauge needle and attach a vacutainer, it seems like the blood would become ridiculously hemolyzed since you'd have a ton of pressure creating a bottleneck through a tiny gauge needle. I suppose you could stick an adult with a 27 gauge needle and slowly draw back a couple of mLs of blood into a syringe (as we do with neonates), but there wouldn't really be any point to obtaining such a tiny sample in an adult. I'm guessing that the vacutainer manufacturers have a recommendation for minimum gauge size to prevent hemolysis based on the mmHg of pressure in the sealed tube.

    It's kind of like the rate discussion regarding running blood products in neonates (i.e. we can run blood through a 24 g IV since our rates are slower), but in reverse.

    Now, if you're manually drawing the blood into a syringe at a fairly slow rate, it seems like you could use whatever size is most appropriate for the animal. With a larger gauge, it seems that you could apply more pressure without the sample hemolyzing, therefore it you could draw it faster....

    Someone, please rescue me from the rabbit hole....
    Last edit by adventure_rn on Nov 19

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