Abbott m2000 quantitative RT-PCR test

[dragonslayer]

Ok.. Here's one to ponder.  This Abbott test is  one of the most common used for viral load testing.  It has a Lower Level of Quantification (LLOQ) of 12... But interestingly, it also has a Lower Level of Detection (LLOD) value of 12.. These values can be seen in the table in the following Abbott doc: 

https://www.abbottmolecular.com/us/products/infectious-diseases/realtime-pcr/realtime-hcv.html

So, how is it possible that my most recent test, performed a wk ago, came back:

HCV RNA:  <12  Detected???

I mean, if 12 is both the LLOQ and the LLOD, then if its too low to be quantified, then its too low to be detected..... right? 

What gives??

[Katie]

The wording makes no sense to me either but that's how it is with research sometimes.  Perhaps they just have some type of indicator and that's why I am thinking it may be picking up on fragments of the broken up RNA from the virus.  I will have to do some more digging on the test to see if I can find anything, but the day is a beautiful one and I need to take advantage of it with positive energy.  Reading all that scientific stuff can sometimes wear me down!  HA! 

Katie 

[Mike]

That is a little confusing.

Here's my understanding:

The quantitative viral test you are referencing has a lower limit of 12, meaning it can provide an exact viral count from 12 to infinity.  However, the test can actually detect the presence of virus below the lower limit of 12- it just can't report a count/number (and has not received FDA approval to do so).

A test result reported as "< 12 detected" means that the test detected HCV virus but could no provide an exact count as it was below the cut off limit of 12 (maybe it was 11 or 7 and so on).

If the test is reported "<12 undetected" no virus was found and it can be assumed the individual is virus free.

However, to confirm an undetected result, the test must be repeated at a later date. This rules out a false-negative and/or the presence of virus below the extreme lower limit/sensitivity of the test.

The initial test results can be confirmed by either a repeat HCV quantitative or qualitative essay.

Since a HCV replicates rabidly - a single virus can replicate in to the millions in 3-6 months - the test is repeated at 12 and 24 weeks intervals (SVR12 and SVR24). If the results are undetected at these intervals, the person is deemed virus free (cured).


Best wishes, Mike

[dragonslayer]

Damn.. Mike I thought for sure youd reply with a well phrased retort as to how you can be detected but not quantified even when the lower limits for both are the same!      Come to think of it, when the lower limits are the same, why even have a Detection limit. Either its quantified, or its not!    Here's another puzzlement.. On this test, when your test reads <12, that scores as  Normal.  The word 'Detected' only shows up under 'Interpretation'.  So, youre not reported as having any HCV anomaly.  So Im thinking with this particular test, if you're <12, since that is beneath the stated lower limit of detection, you're Undetectable, report interpretation be damned!

[DisabledHepcat]

This thread is a good indication how HCV affects the brain.

[dragonslayer]

This thread is a good indication how HCV affects the brain.

Huh?   What.. you dont find this subject interesting and probative, if not a bit anomalous?

[Mike]

To my understanding, a lot of the ambiguity has to do with FDA approval of the tests and what it is allowed to measure and how it can be reported. Hence, the ambiguous interpretative results from the same test:

<12 detected

<12 undetected

This becomes more confusing when you read the test's approved LLOQ and LLOD.

Thus:

"New definitions for an "undetectable" HCV RNA VL

While the goal of treating CHC patients is to eradicate the infection as measured by an "undetectable" HCV RNA result, "undetectable" has evolved alongside the treatment algorithm. For PEGα/RBV therapy, an "undetectable" result was any result that is <50 IU/mL (Table 4).

In contrast, for PEGα/RBV + boceprevir or telaprevir regimens, the term "undetectable" was defined as a "target not detected" result, which was required for patients to be eligible for shorten therapy; but for SVR assessments, a "<25 IU/mL, HCV RNA detected" was an acceptable endpoint.

For the recently approved regimen containing simeprevir, a stopping rule "cutoff" of 25 IU/mL is used at 4, 12, or 24 weeks in which all therapies are discontinued if HCV RNA results are above this cutoff (Table 4). For sofosbuvir, HCV RNA testing is only recommended after treatment after a fixed duration and to assess SVR. Both regimens use "<25 IU/mL, HCV RNA detected" for defining "undetectable".

In the "real world setting" it is likely that there will be less patient compliance than in the clinical trials. Therefore, it may be useful to investigate whether HCV RNA VL "adherence monitoring" on-therapy is worthwhile in patients suspected of noncompliance, especially when considering the high treatment costs.

Given that the trials used a test with a LLOQ of 25 IU/mL, differences in a tests
LLoQ is important. How should clinicians handle a quantifiable result of 22 IU/mL derived from a different test than the one used in the clinical trials (e.g. one that has a lower LLOQ)? These are practical considerations that may cause uncertainty for clinicians.

Using "target not detected" for shortening therapy

With the introduction of boceprevir and telaprevir, new RGT rules were introduced which lead to considerable confusion in the terms used to define "undetectable" and when to apply this interpretation. These rules were based on a re-analysis of the boceprevir and telaprevir trials data that was published by the FDA where it was concluded that a "HCV RNA detectable, <LLOQ" result predicted a significantly lower cure rate compared with subjects with an "undetectable" ("Target Not Detected") result [21]. Based on this analysis, it was determined that a confirmed "detectable but below the LLOQ" HCV RNA result should not be considered equivalent to an "undetectable" HCV RNA ("Target Not Detected") result for the purposes of RGT. Therefore, a "Target Not Detected" result at both 4 and 12 weeks of PEGα/RBV + telaprevir therapy was required to shorten therapy (48 weeks to 24 or 36 weeks of PEGα/RBV). To further add complexity, stopping rules were also different for boceprevir and telaprevir regimens (100 and 1,000 IU/mL, respectively).

Differences between HCV RNA assays with DAA therapies

Although all commonly used HCV RNA assays report the results in the standardized IU/mL, not all tests perform similarly. Several reports have demonstrated differences between how assays report results, particularly in detecting low amounts of HCV RNA [22,23].

In these studies, concordance analyses have determined that HCV RNA differences in reporting results that are "Target Not Detected" versus "HCV RNA detected, < LLOQ" have become apparent.

This is particularly true in one study that investigated results generated from the TaqMan ® HCV Test, v2.0 used as part of a phase III clinical trial with simeprevir plus PEGα/RBV and compared it to Abbott RealTime HCV Test [24]. Overall, there was good agreement between the 2 assays; however, a large number of samples (26%-35%) at week 4 of treatment had detectable HCV RNA levels (<LLOQ) with the Abbott RealTime assay that were "Target Not Detected" by the HPS-TaqMan ® HCV Test, v2.0. These patients received shortened therapy based on the HPS-TaqMan ® HCV Test, v2.0 TND result and high SVR rates were achieved. Thus, if the Abbott RealTime assay results at week 4 of therapy had been used to determine treatment duration, these patients may have been over-treated by an additional 6 months.

Since these DAA-containing triple therapy requires HCV RNA to be TND at both weeks 4 and 12 in order to shorten therapy, differences between HCV RNA assays can affect key medical decisions, in this case resulting in a larger portion of patients treated for longer durations (if the same cutoffs are used). It was therefore suggested that a cutoff of <12 IU/mL (detected) may be appropriate for the Abbott RealTime HCV Test. However, since this cutoff has not yet been clinically validated and further studies are needed."

Link to complete article:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CEUQFjAG&url=http%3A%2F%2Fwww.biomedcentral.com%2F1471-2334%2F14%2FS5%2FS8&ei=H08LVa-cI4e_ggSo3IGoAg&usg=AFQjCNEmpciJX59xDMq3MILfA_dzQoiZyA


Best wishes, Mike

[dragonslayer]

Fabulous find, Mike!!!!   Still so much that isnt known. 

[Mike]

Hi Paul,

I don't want to give false hope (I'm not a doctor); but the more I read about this, the more I think 12<detected may actually lead to an SVR.

We know the virus replicates rabidly, so it doesn't seem feasible (in my opinion) that the virus would hang just below 12 for significant period of time. If there's an active infection, you'd think the VL would climb above 12 in short order.

Clearly, the VL would surpass this limit (12) within a 4-12 weeks.

I got my fingers crossed Bro.

Best wishes, Mike

[Katie]

Thank you Mike.  You have brought some valuable clarification to this.  That is precisely why I need to research in a certain frame of mind as there are so many variables taken into consideration that we as layman don't have access to or find it difficult to understand.  Being personally involved with scientific research (of a totally different sort) and have also worked in a medical field as a histologist for awhile I am probably more aware of this than many and it is one reason, I was compelled to question the meaning of the results and know I may not find an answer, all the while letting me get hope and peace of mind while I waited for my next bout of blood work. 

The information you posted pretty much confirms what my thoughts have been and so I will therefore move on in a very positive frame of mind.

Thank you again, and Thank you Dragonslayer for pushing forward with your concerns and questions.  You'd make an excellent scientist!     Some of us just need to look into things affecting us more and not just accept what is given to us.  My doctor doesn't even understand this and is a brilliant, caring doctor, so I will be sharing this information with him.

Katie

[dragonslayer]

Hi Paul,

I don't want to give false hope (I'm not a doctor); but the more I read about this, the more I think 12<detected may actually lead to an SVR.

We know the virus replicates rabidly, so it doesn't seem feasible (in my opinion) that the virus would hang just below 12 for significant period of time. If there's an active infection, you'd think the VL would climb above 12 in short order.

Clearly, the VL would surpass this limit (12) within a 4-12 weeks.

I got my fingers crossed Bro.

Best wishes, Mike

Hey Mike. This was precisely my doctor's take.   From the article, I thought that the section discussing the Not Detected results using the TaqMan test vs the Abbott test during the Simprevir plus PEGα/RBV trial was most interesting...  Apparently, it was determined that a 'detected < LLOQ(12)' from the Abbott test  was a close enough equivalent of a 'Target Not Detected' from TaqMan in order to produce a similar response to treatment :

"It was therefore suggested that a cutoff of <12 IU/mL (detected) may be appropriate for the Abbott RealTime HCV Test" in order to produce a therapeutic change to treatment equivalent to that produced by a 'Target Not Detected' result from TaqMan.

Although it was followed by the caveat: "However, since this cutoff has not yet been clinically validated and further studies are needed."

[Mike]

HCV treatment is advancing so fast, the undetected quantitative measures can't even keep up!

Best wishes, Mike

[Junkyard]

Bottom line is, after treatment not having the bug multiply. I think length of treatment can have as much to do with relapse as anything. From what I have seen adding riba is the real trick for those of us that are the hard to treat.
Gilded wants it to sound like they have this thing by the ying yang, but, we won't know for a while. That is why my doc and I have a plan to at least apply for another 12 weeks if anything at all looks like it won't work. I am wore out with treatment, it's time to be done with this and start living again.
Good luck to all

[dragonslayer]

Very much related to this subject, check this out:

http://download.springer.com/static/pdf/727/art%253A10.1007%252Fs00430-014-0364-z.pdf?auth66=1427059062_55c594ee9807351df44f53d9574cf761&ext=.pdf

If nothing else, read the conclusion!

[sapphire101]

Dragonslayer can you post the conclusion to your link?
For some reason I can not open it.

[dragonslayer]

Yea, I dont know what happened to that link.. .It died after I posted it.. Ill keep looking for the article.

[Katie]

it opened up for me on the Research site where DS also posted it.

Disregard as it isn't working now.