Accuracy
and reproducibility of ultra-low genotyping
Rob Lloyd is with
Applied Sciences Lab and Visible Genetics Inc. Visible Genetics Inc is located
in Toronto and manufactures TrueGene genotypic resistance test. Applied Sciences
is in Norcross, Georgia. It has generally been accepted that if a person’s
viral load were above 1000 copies/ml a lab would not be able to test their blood
sample for resistance. In fact if a person’s viral load is below 1000
copies/ml some labs will not accept or discourage submission of the blood
sample. But many individuals with <1000 copies/ml of VL would I think
justifiably like to test themselves for resistance.
Lloyd
reported he detected genotypic mutations from actual samples of individuals in
this study. He said sequence results demonstrated reproducible and accurate
genotypes between duplicate samples at low viral loads down to 60 copies/ml. In
speaking with Lloyd he has told me he can detect genotypic resistance mutations
when viral load is below 50 copies/ml. In all fairness this data ought to be
considered preliminary and should be subjected to confirmatory studies. A few
other researchers expressed doubt or uncertainty that you could in fact reliably
and reproducibly detect genotypic mutations when viral load is very low (<50
copies/ml). If you have a low viral load and request genotypic resistance
testing, I would be cautious in interpreting and relying on the results. One way
to address this question would be to submit 2 or more samples to the same lab
and see if the results are the same. If your viral load is <50 copies
performing resistance testing may offer information but its utility may be
limited because you are not going to change your regimen. But if your viral load
is several hundred to 1000 copies/ml detecting resistance may help in deciding
to modify your regimen and what drugs to use.