Adam’s Journal
I promise I’m going to give Covid and flu topics a rest soon – just as soon as those viruses leave me alone.
Not long ago, I was feeling rundown and had post-nasal drip, a sore throat and a headache. I feared it might be the flu, so I thought I’d better get a home test to check.
When my wife went to the drugstore, she came home with a test – now widely available – that looks for two strains of flu, plus Covid. After following the instructions, the control line showed, but nothing came up for the flu. However, a faint line did appear for Covid.
I had just recently had Covid, so I was surprised to be positive again. But did the faintness of the line mean my case wasn’t serious?
Dr. Scofield Prescribes
Home flu and Covid tests are designed to tell you whether you are sick or not. They are not, however, designed to be quantitative – which means telling you just how sick you are. Indeed, the Food and Drug Administration has not authorized the tests to do that.
Nevertheless, the results of the test do hinge on how much virus is in the sample you provide. They use antibodies, which are immune system proteins, that react to a part of the viruses – antigens – that cause Covid and flu.
When you are looking at the line on the test, you are actually looking at millions of tiny antibodies clinging to dye. And the reason they stick to the line on the test is that they’ve also latched onto virus antigens.
That means the heavier your viral load, the more tiny dye molecules will stick to the line. In other words, if you have lots of virus in the sample, the line will be darker.
Now, it matters when you take the test. If you take a test at the outset of your symptoms and a faint line appears, that could just mean you’re at the beginning of an infection, and viral levels will continue to build in your body. Conversely, if you’ve been sick for days and you see a faint line, that could mean you’re at the tail end of the virus.
To get a better picture of what’s happening with viral levels, you’d want to take tests throughout your illness – using the same brand of test throughout – and watch how the line coloration is trending. Still, you should be careful not to place too much emphasis on what you see.
Human error can play a role in the process: If you don’t swab thoroughly, then the results won’t be an accurate indicator of viral levels. And if you feel terrible but see a faint line, don’t assume you just have a mild infection and will be fine.
Still, if you carefully and systematically use testing to monitor your infection, they can provide useful information about how sick you are and whether you’re on the road to recovery.
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Dr. Hal Scofield is a physician-scientist at the Oklahoma Medical Research Foundation, and he also serves as Associate Chief of Staff for Research at the Oklahoma City VA Medical Center. Adam Cohen is OMRF’s senior vice president and general counsel. Send your health questions to contact@omrf.org.
