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 personís viral load were above 1000 copies/ml a lab would not be able to test their blood sample for resistance. In fact if a personís 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.