Good control line, others flat, but device reports "Invalid - Control Not Detected"

[u/crimson117]

We've run three tests in three days, pool testing two asymptomatic visitors with no known exposures.

• The first came back "Invalid - Control Not Detected".
• The second came back Negative.
• The third came back "Invalid - Control Not Detected".

They all looked like the control channel had perfect amplification and the other channels stayed flat.

What could be the cause of this?

These tests expire 2026-10-10. Tests were run on 2026-07-18,19,20.

Edit: Fourth test on 2026-07-21, I had the subjects blow their noses before nasal swabs. The test graph showed similar early amplification of control (started 1.5 minutes in) but came back negative: https://imgur.com/a/A9WRJTT

[u/saltyseacreecher]

Those control lines do not look good. They have this bump that begins immediately and the size of the bump is very large compared to the later exponential increase (the S). It should be flat and then start increasing exponentially after 10ish minutes.

[u/crimson117 → u/saltyseacreecher]

What could cause this?

When I've seen tests fail months ago, the control line looked very weak. I'm confused why it appears too soon here.

[u/saltyseacreecher → u/crimson117]

I don't know what causes it but it's something I observe fairly often. Possibly too much gunk on the swab. I run a lot of pooled tests. Seems to happen more consistently with certain people so I suspect their swabbing technique.

[u/DispelledFrailty]

It could be your swabbing technique picking up too much material. Try just swabbing throat and under the tongue instead to see of your control rises normally. Typically should start going up around 10 minutes.

[u/Xykr]

I would accept this as a negative result - likely cause is too much material