Genotyping at low viral loads

[zellyf]

I was recently genotyped with a viral load of probably well under 2000 copies/ml.  Steven, I noticed some things you wrote that suggested a higher viral load was required to determine genotype.  Does that make my results suspect?

[stevenNYer]

I think so, if the sample they used happens to have some nice virons in them.  In my genotyping, in areas where they can't determine, it indicates "can't be determined".  I don't think the labs would guess just to make up some info.

[zellyf]

So, simplifying so that I can understand...you think its possible to get an accurate genotype with only 140 copies/ml?

[stevenNYer]

HBV DNA is a snap shot of the viral load at that specific time.  When your DNA is in the millions, logic would indicate that the tube your MD drew for genotyping will have lots and lots of virons in it for them to do sampling.  If your VL is low, there may not be alot of virons in that tube.  But if there is one nice virus sample, they used it to figure out the genotype, and not the other things.  This would be my guess.

My doctor did say genotype at this point won't determine treatment.  This is unlike HepC where genotyping is so important.

[zellyf]

The same labwork that gave me the genotype also showed my viral load to be 140 copies/ml.  I'll check with my doctor.

[cally44]

Unless the labs made educated guesses, the genotype without a sufficient amt of viral load cannot be detected..Sixto a research company is currently trying to find heppers who have a high vl to see the genotype differences.  When I told them mine was detected to be D with undetectable viral load they said that was probably a guess or an error b/c pple in the far east regions tend to be D.

I know Genotype C is harder to treat and there is more risk of cirrosis what about genotype D...any info?

[zellyf]

If they couldn't get your genotype at 10,000 then how did they get mine at less than 2000?

They were able to determine that there isn't antiviral resistance but not whether or not I had the PC or BCP.

Thanks!

[stevenNYer]

No it doesn't, it had enough to determine the genotype.

When my GI order "genotyping", it checked for the genotype, mutations, and antiviral resistance.  So I think the higher the viral load, the better samples they could pull for determining those mentioned items.  

If the viral load is low, then perhaps you only get bit and pieces of information.  So for you they may have had enough to determine the genotype but were inconclusive on other items.  

I did my 'genotyping' at about 10,000 copies, so several of the items were inconclusive.  Couldn't even determine the genotype and couldn't determine presence of antiviral resistance.

Especially for mutations, a good percentage, like 10 to 30% of the quasi-species carrying the mutation needs to be present before the test is able to pick it up.  Otherwise, it's easily missed.