Below the Level of Quantification
Feb 17, 2013
Dr. Holodniy, I run a support group for newly diagnosed folks. One of the primary concerns for people new to medications is getting to their first undetectable viral load. In the past results would have either been a specific number, or if the results were below the level of detection, the result would be < (less than) the lowest level of quantification (or undetectable). More recently we've had a few group members who have received a result of "below the level of quantification" or BLOQ. Is there any clinical significance to this, as opposed to the old "undetectable?"
We've talked in the group on how the tests are becoming more and more sensitive. A result of 35 today would have been undetectable just a few years ago. As these tests become more and more sensitive, I expect that eventually the term undetectable will eventually disappear, and everyone will have some number, perhaps only a single digit. At some point, we'll need to have a clinically acceptable cut off number. We're not there yet, but would a BLOQ result mean anything different to you as a provider?
Response from Dr. Holodniy
For me, no it doesn't mean much. You are correct, in that the assays have become more sensitive (lower threshold for positive detection), whereby the assay can still report a result as positive but the assay is not reproducible enough at these very low levels to report a precise number. The jury is still out as to the significance of this. You will find experts on both sides, where some say the viral load needs to be at "zero" and others who say "undetectable" is just fine. The literature is also conflicted as to the significance of detectable, but not quantifiable levels, with some papers reporting there is a higher risk of virologic failure and others reporting there is not.
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