"<43" vs. "not detected"

(LT = Less than, ha, I have a real problem with brackets.)
This week had an appt. and I'd like to get responses for a couple items
1) on VL tests, all called, HCV RNA BY PCR have come back either
"RNA by PCR LT43 IU/ml" or "HCV RNA not detected."
All the first VL tests were the LT43 type, since then all are not detected.
They are saying LT43 is NOT the same as not detected. This kinda stunned me because I thought the detection limit of this test was 43, so even if you went to zero it would still read LT43.
Why are they making a distinction?

BTW this works for me because of the second item. They say that tx continues for 6 months after one becomes "not detected." Has anyone heard this before?

[eureka254]

My husband had a similar situation early in treatment, and the way it was explained to me was that some labs will still give a qualitative positive result below their cut-off if RNA virus is detected. At week 12 the lab my husband was using had a <50 cutoff, and he similarly had a result that was "less than 50 but detected."  The nurse explained that the lab used didn't quantitate between 5 and 50 (in your case, it could be between 2 and 43, I suppose), so since that time my husband's been using Heptimax by Quest which uses <5 as their cut-off.  Incidentally, he had "less than 50 but detected" at week 12 and had a redraw at week 13 and was "undetected <5."  In his case, he was recommended to do 72 weeks, so I'm not familiar with the policy of continuation for 6 months after undetected policy.  Perhaps someone else who has will weigh in on that.  Hope that helps, and wishing you much luck with treatment. ~eureka

[Trinity4]

Minimum of 36 wks UND after initial UND is what I was told.  Maybe that's only for those who reach UND by 12 weeks because had that formula applied to me I could have stopped at week 60.

Trinity

[Andiamo1]

Some tests have quantitative results that are not as sensitive as qualitative results.  For example, the test used by Vertex for the prove 3 trial had a quantitative sensitivity of greater than 30 and qualitative sensitivity of greater than 5.  In other words, the test can tell you still have the virus, but can't produce a count if it is less than 30.

This means if your viral load was greater than 30 you would get the actual number.  If it was between 5 and 30 you would get a result of less that 30 detected; if it was below 5 you would get a result of less than 30 undetected.

Hope I didn't confuse things further.

[neptune235]

There are two components to the test, a qualitative (pos / neg), and a quantitative (a number).

If your viral load is less than the numeric detection limit of the quantitative, portion of the test, but test positive for the qualitative portion, it means that you still have a very low level of viremia.

If, however, the qual comes back neg, then you are UND.

[Kristina538]

I had the <43 on my 4 week test;  my specialists were so excited that I was RVR, but I debated and worried over maybe needing an extension beyond 24.   In layman's terms I was told that it was 'as good as' especially if it's a result early in tx, and the likelihood of it being UND within the following week was high;  so I probably become UND between week 4 or 5.    For a G3A on 24 weeks tx, that was important, as treating for 24 weeks after UND had been a recommendation.

I'm supposing here that it's important when the test was taken and what relevance it has to the tx outcome/extension.   My <43 result at week 4 had given me a better prognosis for success than obtaining anything greater, but it was a fine line, to me, as to whether the 24 weeks would be quite enough.   At 4 weeks, however, it did show that my body had good response to the meds, which was heartening.