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Here’s my non-medical explanation of the difference between UND and < 15. * Once we get down to a very small numbers of virus particles, it is no longer a question of medicine or even biology. It all comes down to chemistry, equilibria, and probabilities. Anyway, I'm not a doctor, but I do know a bit about chemistry and biology, so here goes: * Its important to remember that both quantitative and qualitative HCV RNA tests measure the amount of RNA from the virus in the bloodstream. They do not measure the number of actual virus particles (virions). The viral RNA is just one part of the package, so to speak. * The qualitative test gives a yes/no answer, but a quantitative test gives a numerical count, unless it is less than about 15 units, in which case it is a yes/probably answer. But for someone on DAA treatment it is more like a "no" answer. Or more precisely, a "going to be no" answer. Confused? Don't be! * We normally think of the virus as a solid particle, but in fact it is better to think of it as a population of particles. Some of them are useless, some of them are falling apart, and some of them are spontaneously re-assembling into new viral particles again. But most of the time they just fall apart naturally. Otherwise, they would be perfectly harmless. So when a blood test detects viral RNA, it is actually detecting bits of RNA from those particles that just by chance have fallen apart at the time of the test. * Clearly, if there are no HCV virions present in the blood sample, then should be absolutely no HCV RNA present. * But suppose you have just dropped a strategic nuclear warhead on a few trillion virions. Most of them will be absolutely destroyed (cut to shreds, vaporised, atomised, whatever).... But quite a few will only be cut to shreds and not vaporised. In other words, many of the viral fragments can persist for quite some time in the body (and so are still detectable), even though there is not enough of the right pieces to make new virus particles. So it is quite likely that very low but still "detactable" levels of HVC RNA can mean no viable virions left - or not enough viral fragments are left to be able to spontanously re-assemble again, which comes down to the same thing. * On the other hand, maybe a few virions might survive the nuclear blast intact. But if you are down to just a very few, it is unlikely that there will be enough of them to replicate because a whole sequence of "chance" biological events have to take place in order for the virus to replicate successfully. And in order for that to happen, there needs to be enough copies of the virus (i.e. enough viable virions) in the first place so that all the necessary chance transfers and collisions and biological/chemical reactions can take place... And if you are down to just one virus particle, there is a very good chance that it will just fall apart and none of its components will ever arrive in the right place to re-assemble or to carry out the replication process. So once you are down to the last few stragglers, there is a good chance the virus will disappear naturally. * And also don't forget that once infected, the body has developed antibodies which hunt down and destroy most of the virions on a daily basis... The problem with chronic HCV infection is that the speed of the hunt-and-destroy process is about the same as the speed of the virion replication rate, so the body never manages to clear the virus by itself. But the nuclear blast does not affect the antibody system. So again, very low but "detectable" HVC RNA means a high probability that the virus will clear because the antibodies are still busy with their (less than perfect) detect and destroy mission... * This all means that it is quite possible to have "detectable" but very low (or even "unquantifiable") RNA tests all the way during treatment, and then only becoming "UND" several weeks or (even months) after the treatment has finished. Me, me viral load was < 15 after 4 weeks. So I am pretty confident that I will eventually become "UND" in a quantatitive PCR test. But it is just a matter of time... Oops, I mean it is just a matter of chemical equilibria... and at the end of the day, this means just a matter of probabilities.... So to cut a long story short, my (non-medical) advice is also if you get to < 15, don't worry! You're well on the way to "UND"... But nobody can promise how long it will take...
http://www.questdiagnostics.com/testcenter/testguide.action?dc=TH_HCV_RNA_QualTMA
http://www.hepatitis.va.gov/patient/hcv/diagnosis/labtests-RNA-qualitative-testing.asp
Thanks Vororo, very well explained. 
……it would seem young William learnt more at scuil than he lets on to his teacher.
G3a since ’78 – Dx ’12 – F4 (2xHCC)
24wk Tx – PEG/Riba/Dac 2013 relapsed
24wk Tx – Generic Sof/Dac/Riba 2015/16 relapsed
16wk Tx – 12/01/17 -> 03/05/17 NS3/NS5a + Generic Sof
SVR7 – 22/06/17 UND
SRV12 – 27/07/17 UND
SVR24 – 26/10/17 UND
splitdog wrote:The way I understand it, ‘Quantitative’ testing determines the actual number per ml of bloodborne virus. However, it is only accurate between 12 and 10,000,000. The ‘Qualitative’ testing is far more accurate, but can only determine present/not present. So you use quantitative to see how you’re doing until <12, then do qualitative to see if it goes all the way down to undetected. (zero). Dr. Freeman?
Hey splitdog, pretty much. Check out the Doctor's cheat sheet link for a summation
Monitoring
Now the patient has access to the medications here is what monitoring on treatment looks like:
Baseline FBC, Cr&E, LFTs, Hep C Viral Load with reasonable currency + AFP and liver ultrasound for those with cirrhosis (looking for HCC)
4/52 into treatment FBC, Cr&E, LFTs, Hep C Viral Load
Repeat Viral Load at 4/52 intervals if not zero at 4/52
EOT (End Of Treatment) exit bloodsHep C Viral Load can be quantitative (undetectable, <15, or 15-100,000,000) or qualitative (undetected/detected).
http://fixhepc.com/getting-treated/how-to-do-it/doctors.html
Thanks too for the great exposition Vovoro, very well explained
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