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AJL

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Posted 18 June 2022 - 08:41 PM

Hi!

Hoping from some math brains to pop up here and save me!

I have found some great allergen (gluten) swabs with detection limit of 4ug/25cm2. 

When I sent the swabs in to the lab to get a validation, the units come back in g/L. 

How do I convert so I end up with the same units? It would just be great to know how close to the LOD I got to with the positive result. The lower the better, then I can see that my swabs work close to the LOD. 

THANKS in advance 



Charles.C

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Posted 19 June 2022 - 07:35 AM

Hi!

Hoping from some math brains to pop up here and save me!

I have found some great allergen (gluten) swabs with detection limit of 4ug/25cm2. 

When I sent the swabs in to the lab to get a validation, the units come back in g/L. 

How do I convert so I end up with the same units? It would just be great to know how close to the LOD I got to with the positive result. The lower the better, then I can see that my swabs work close to the LOD. 

THANKS in advance 

Hi AJL,

 

I assume the "swab" delivered to lab was a "swab"  immersed in a liquid (S).

I assume swabbed area was 25cm2

I assume "ug" = microgram

 

volume of S = X  litre

lab result = Y g/litre

Relevant allergen (gluten) in swab = G

 

Then (With a few assumptions) -

Quantity of G associated with swabbing area of 25cm2  = XY grams = XY x  106 ug

 

Can compare to 4 ug

 

JFI this example might also intrigue you -

 

https://www.factssa....sked-questions/


Kind Regards,

 

Charles.C


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AJL

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Posted 19 June 2022 - 09:36 AM

Thanks Charles,
The swab was not immersed in liquid, but the swab was slightly moistened. The lab must have immersed in a standard amount of extraction solution, which I do not know.
Yes ug=mcg.
Yes swabbed area is 25cm2.
I assume this means that I cannot complete the conversion unless I know the amount of liquid which the lab used for the submersion?
I am not impressed by the units they used, I would have preferred g/swab. I will read the link you shared. Thank you!!



Tony-C

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Posted 20 June 2022 - 03:06 AM

Hi AJL,

 

I would ask the Laboratory for a copy of their test method, that should explain their reporting. Post it here if it doesn't make sense.

 

Kind regards,

 

Tony



AJL

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Posted 20 June 2022 - 03:41 AM

Thanks Tony 👍 good point



Charles.C

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Posted 20 June 2022 - 07:32 AM

Thanks Charles,
The swab was not immersed in liquid, but the swab was slightly moistened. The lab must have immersed in a standard amount of extraction solution, which I do not know.
Yes ug=mcg.
Yes swabbed area is 25cm2.
I assume this means that I cannot complete the conversion unless I know the amount of liquid which the lab used for the submersion?
I am not impressed by the units they used, I would have preferred g/swab. I will read the link you shared. Thank you!!

Hi AJL,

 

Re ^^^(red) - Yes, you will presumably need some feedback from Lab. The quantitative process is not exactly "simple".

 

Are you using a particular commercial Product/testkit ?  If so, which one ? (This should detail how to proceed or offer technical backup on request).

 

The ELISA methodology typically requires extraction of the allergenic protein from the swab. The extract is then sampled/analysed.

 

JFI, I noticed this caveat for one commercial system -

 

How long can sample extracts and swabs be stored before testing?
Swabs can be stored for up to 24 hours at 4°C after sample collection provided they have not been extracted yet. Once extracted, samples from swabs should be evaluated within 4 hours. All other sample extracts should also be tested within 4 hours.

 

PS - you may also find this Production-oriented illustration of interest although (a) the included  VITAL-interpreted material likely has geographically restricted useability and (b) note the words "extreme" /  "homogeneously" :smile:  -

 

https://www.zeulab.c...l-de-alergenos/


Kind Regards,

 

Charles.C


AJL

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Posted 20 June 2022 - 07:51 AM

I am using Römer labs rapid test kit, the lab I assume is using Elisa, with result in g/L



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