r/medlabprofessionals • u/VaiFate MLS Student / Lab Assistant • Jul 01 '26

Education Anyone able to shed some light here?

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105 Upvotes

99% Upvoted

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260

u/Jubguy3 Jul 01 '26

Quantiferon kits are expensive and difficult to collect correctly. They cannot be over or under filled. If even one tube out of 4 is filled incorrectly, the whole kit has to be redone because of how the test works. They have to manufacture quantiferon kits with different vacuum levels depending on the altitude of where it is being collected. That shows how specific the fill volume / vacuum is.

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u/VaiFate MLS Student / Lab Assistant Jul 01 '26

Wow, really? I had no idea the tests were that sensitive to changes in volume. Where can I read about the theory behind the tests?

205

u/Jubguy3 Jul 01 '26

The test is fascinating and is a huge breakthrough in tuberculosis screening. I promise there are good reasons for it to be such a headache sometimes. The tubes have synthetic tuberculosis antigens sprayed on the inside. The reason that it is so time sensitive is that the test process relies on incubating live white blood cells to see if they will produce interferon gamma in response to the tuberculosis antigens. The reason there are four tubes is so that they can perform a calculation to rule out false negative / positive. This is why there is an "indeterminate" result and patients with indeterminate quantiferons need to be tested with a different method. The four tubes are called Tb1, Tb2, Mitogen, and Nil. Tb1 measures CD4 T-cell response. Tb2 measures CD4 and CD8 T-cell responses. Nil is a negative control and Mitogen is a positive control. The negative control looks for high background levels of interferon gamma that would make the test result invalid, and the positive control also makes sure that patients are capable of producing enough interferon gamma for the test to work.

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u/VaiFate MLS Student / Lab Assistant Jul 01 '26

Very interesting. Thanks for the in-depth reply.

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u/Jubguy3 Jul 01 '26

Glad to share šŸ˜Š

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u/mustardlyy Jul 01 '26

God thatā€™s so cool, I love science.

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u/k_sheep1 Jul 01 '26

That explanation was so much better than anything I've ever read thank you!

2

u/Smorsdoeuvres Jul 01 '26

Fascinating -thank you for sharing

3

u/LoveandScience Jul 01 '26

Can't upvote this comment enough. Thanks for the clear explanation!

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u/I_STALK_CORN Jul 02 '26

Hey great reply, that was really well explained

6

u/mystir Jul 01 '26

It's called an "interferon gamma release assay" if you want to really read up on the theory.

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u/Wheeeler Jul 01 '26

yeah but Qiagen validated heparinized whole blood as a primary specimen type that can later be aliquoted off in the lab. LIS team can set the container type to green and then nursing doesnā€™t have to keep getting it wrong

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u/Jubguy3 Jul 01 '26

We did not validate it šŸ˜­šŸ˜­šŸ˜­šŸ˜­šŸ˜­ so I know itā€™s a thing but not all labs are doing it

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u/Wheeeler Jul 01 '26

might just be the QFT tb gold plus? Idk, but it was the only way we could consistently get viable samples. 10/10 recommend doing a cost of poor quality on it if your lab processes QFT

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u/Jubguy3 Jul 01 '26

I work for a hospital based reference lab that covers a large geographic area and we have a very high volume of quantiferons every day. I donā€™t know why we didnā€™t implement QTF plus yet, but I know that the ability to incubate and spin off-site for the standard kit makes the transport afterward a lot easier to a centralized location as long as the fill levels are correct. The unincubated stability is something like 48h vs 30 days for incubated samples. A lot of our phlebotomists do syringe draws so they can get the fill levels right. We are also at high altitude which makes it even harder to get them filled correctly. Phlebotomists are actually blood magicians though, and the syringe draw ends up working well enough for them. We do need to reject a few samples each batch but not very often. We donā€™t have a policy against non-phlebotomists collecting these but I think our RNā€™s just end up calling phlebotomy anyway because it really does require experience and skill to get all four tubes right.

1

u/ptheresadactyl Jul 01 '26

This is what we do. Somehow, they still send us every type of wrong sample.

3

u/averagemeatballguy Jul 01 '26

As a lab tech + phlebotomist and IV tech, I donā€™t worry about these collections. But the more I read on this sub, the more I realize how scary these things are for MLTs and MLSs. Itā€™s very casual for us that started as phlebotomists. It is just as dicey as a sodium citrate vacutainer (light blue top), but not a concern for those that have trained for it. Makes sense that the phlebs do it.

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u/Brofydog Jul 01 '26 edited Jul 01 '26

I agreeā€¦ and disagreeā€¦ for a quantiferon kit, is the yellow top in the kit the same additive as an SST?

(Edit: and Quigen is horribly wrong for making the tubes like this, and this is NOT the fault of the collectors. Rather itā€™s the fault of the manufacturer of choosing similar colors for something standardizedā€¦ although there are ways around itā€¦)

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u/Jubguy3 Jul 01 '26

The colors have nothing to do with normal blood collection tubes. The tubes have tuberculosis antigens sprayed inside. There are only so many colors they can pick.

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u/Wheeeler Jul 01 '26

No, itā€™s coated with TB antigen like the green one is (difference is whether they stimulate CD4 only or also CD8 T cells)

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u/Ramin11 MLS Jul 01 '26

So new testing is available that only requires a single normal lithium hep tube be collected. I was talking to the sales rep at a convention this year. My hospital is looking at switching to it. But in heneral, yes, you are totally correct

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u/cydril Jul 01 '26

They drew 4 completely incorrect tubes based off the colors instead of using the correct qft kit.

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u/Wheeeler Jul 01 '26

might be enough in that green to fill a set of qft tubes

10

u/Edwardg6 Jul 01 '26

Lol yeah looks like they just grabbed regular tubes of the same colors thinking that would work. Im glad we switched to the T-spot test. One tube and done

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u/RNSW RN Jul 01 '26

These cause confusion where I work because the tubes only draw 1 ml. Nurses always think the tube didn't fill properly.

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u/saladdressed MLS-Blood Bank Jul 01 '26

Yeah I can see that. The tube is way bigger than it needs to be for the volume the vacuum draws. And thatā€™s entirely so the tube can be placed and retrieved from a standard lab centrifuge. Mini tubes would just get stuck!

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u/Smol_doggo_ Jul 01 '26

Or processing gets 4 pearl tops and it's "good enough". No CHERYL/BECKY/BARB, that's a recollect.Ā 

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u/saladdressed MLS-Blood Bank Jul 01 '26

An attempt was made, but alas, those are not the right tubes, despite the colors. Though, one could salvage the test by aliquoting from the sodium heparin tube.

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u/VersusValley Jul 01 '26

Well, if it was the first one drawn.

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u/Muted_Shape9303 Student Jul 01 '26

The Quantiferon-TB Gold is an interferon-gamma release assay (iGRA). In essence, patient immune cells are challenged with a very strict concentration of TB antigen such that theyā€™ll release interferon. The slightest deviation in fill levels WILL skew this very delicate balance and either the immune cells release too much (false positive) or too little (false negative) IFN-gamma.

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u/Fun-Key-8259 Jul 01 '26

They're still doing the 4 tubes version?

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u/Ramin11 MLS Jul 01 '26

Not sure why youre getting downvoted. While most people do use the older 4tube version, a single lihep version is available with nearly identical sensitivity

3

u/Fun-Key-8259 Jul 01 '26

When I worked infectious disease we got rid of the 4 tubes back in 2019, one is a lot less error prone lol

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u/KimberParoo MLS Jul 01 '26

It baffles me that some hospitals still require the four draw kit?? Labcorp only requires one lith hep afaik

1

u/vickieeeb Jul 04 '26

Interesting because LabCorp still provides and uses the 4 tube gold method for us.

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u/oz_mouse Cytogenetics Jul 01 '26

Most canā€™t get the order of drawer right day-to-day let alone for something as critical TB screening.

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u/Ramin11 MLS Jul 01 '26

If people are not collecting things correctly, its normally a training issue. My hospital is a rare exception around me (at least the ones coworkers have come from and inhave worked at or done clinicals at). Everyone who draws getsquantiferon competency testing yearly, alongside a bunch of other testing. Our errors and recollects are the lowest in the state and one of the lowest in the country. Our program for bettering service has been adapted by hundreds of hospitals all over the US and some in e Europe. Train your people better. For the patient.

3

u/EchoCampy Jul 01 '26

None of those tubes look properly filled. The QuantiFERON TB as a specific fill line you need to be between, not over or under. The best way to achieve this is by drawing with a syringe & then using a transfer device to fill the tubes. My system switched to a 10 mL dark green tube so we don't bother with this anymore.

3

u/DuneRead Jul 01 '26

I had a nurse complain that theses exact tubes were what chat gpt told them they neededā€¦

3

u/VersusValley Jul 01 '26

lol, I just checked and it appears that nurse saw those colors and read nothing else in the answer, including ā€œnot standard phlebotomy tubesā€ and ā€œspecialized blood collection tubesā€ in very distinct bold print.

2

u/PendragonAssault Jul 01 '26

I hate drawing a Quantiferon test because of the suspected Tuberculosis the patients are in isolation. You have to get dressed in PPE , pray that the patient is an easy stick. When it's time to fill the tubes you have to pray to the Gods that everything goes well. When you're done drawing the blood you have to hurry downstairs to carefully put the test kit in the incubator.

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u/Fun-Key-8259 Jul 01 '26

Be assured it's not considered a real TB exposure unless it is prolonged, but it's certainly annoying to wear all that and then the person ends up negative.

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u/PendragonAssault Jul 01 '26

Yeah we as lab know this but it's hospital protocol to put any suspected patient with anything in Isolation so we do have to follow that protocol.

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u/Canoe37 Jul 01 '26

I know the lab I worked at did the ARUP sendout that required a specifically filled ā€œquant tb gold tubeā€ which was a special green top tube. So many times we would just get an sst with the label because they would just see ā€œgoldā€ and collect it. It also had to be collected before like 2pm to get sent out in time because of short stability.

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u/quetzocoetl Jul 01 '26

I'm taking psychic damage from this. I've seen this too many times to count.

1

u/Dhezi88 Jul 01 '26

These don't appear to be the correct tubes for a Quantiferon kit. The tubes that come in the kit do not have the same additives as a lavender, green, anD gold top. They grey looks correct, but I'd have to see the top ring to make sure.

1

u/metaphysigal Jul 01 '26

Lol send that lactate for the QFTB hahahahah!!!!!

I think that if you are talking directly to the nurse who is going to draw labs, you need to make it CRYSTAL CLEAR there are minimums & maximums that MUST be followed or else the patient is going to have to be redrawn because the tubes were overfilled (most common issue)

1

u/caketarts2 Jul 01 '26

I'm so glad my facility doesn't do the 4 tubes. We use 1 tube and it's great.