Question about discordant HBsAg results — positive qualitative but undetectable quantitative
I’m trying to understand some confusing HBV lab results and would appreciate some insight from anyone familiar with HBsAg testing.
I have chronic HBV and am currently being followed by the NIH as part of a clinical trial. My HBV DNA is currently <10 IU/mL (detected but below quantification).
On 9/28, from the same blood draw:
Qualitative HBsAg with confirmation: POSITIVE
Quantitative HBsAg: <0.05 IU/mL (reported as undetectable)
HBV DNA: <10 IU/mL
What really confuses me is that the quantitative HBsAg was repeated two days later (9/30) and was again <0.05 IU/mL.
Has anyone experienced a situation where the qualitative HBsAg is confirmed positive, but the quantitative HBsAg is below the assay’s detection/reporting limit?
I’m trying to understand whether this could simply be due to the different assays/detection thresholds, or whether it indicates extremely low-level HBsAg that the quantitative test can’t measure.
Would appreciate any experiences or explanations from people familiar with HBV testing, especially if you’ve had similar results.
The linear range for the cobas (R) HBV quantitation for a 500uL sample processing volume is from 10 IU/mL (lower limit)to 1.00E+09 IU/mL (upper limit). Accuracy is within+/-0.24 log10.
@A350driver Yes, I had this happen to me recently following treatment with bepirovirsen. My HBsAg was <0.05 for 6 months, but one of those draws came back with the qualitative test result positive. Upon repeat testing, the qualitative stayed positive, and quantitative also eventually became detectable again as well. I think I remember you saying that you were on interferon. If you’re coming off of interferon now, it could be the start of HBsAg coming back, like ti was for me, but if you’re still on interferon, it might just be a blip or something.
This is likely due to how the tests report very weak results. Qualitative tests return yes-no results, whereas quantitative ones report specific values. Most quantitative tests break down at very low levels of signal because it is just really hard to consistently detect such low levels with enough precision to report a number. My conservative interpretation from your description would be that you are HBs positive, but that the level is extraordinarily low.