- Even if it is faint, a positive line result on a rapid antigen COVID-19 test indicates that you are sick and likely contagious.
- For those who are recovering, the opaqueness of the results window and its positive line may indicate that your viral load is lower than levels recorded in earlier tests.
- Read on to learn more about faint lines on home rapid antigen COVID-19 tests.
With experts concerned about a tripledemic, at-home COVID-19 tests are an essential tool to keeping healthy in 2023 — and pharmacies, department stores and public health clinics have plenty of easy-to-use options these days. Many of the take-home tests carrying an emergency authorization from the Food and Drug Administration (FDA) make use of a control panel and a results window. In most cases, if a secondary line appears in the results window after a nasal swab is submitted, it signals that the test is positive. But users often lament (and commiserate!) when these tests return a result that isn’t exactly clear; a faint line in the sample window that may not look as defined as a test’s manufacturer portrays in testing instructions.
It’s true that rapid COVID-19 tests aren’t foolproof — user error can occur if instructions aren’t followed carefully. So does that mean that a faint positive line may be misleading? Sadly, this is likely not the case, either. Existing research highlighted by experts at Massachusetts General Hospital indicates that a false positive is rare; in fact, a false positive is more likely to happen at the end of a COVID-19 illness than when SARS-CoV-2 initially infects someone.
If you’re able to see a line of any shade or depth in your COVID-19 test’s results window, you are indeed sick and likely contagious to others around you, says Emily Volk, M.D., FCAP, the president of the College of American Pathologists. “It’s binary, right? It’s either negative or it’s positive — it’s like a home pregnancy test. You can’t be a little bit pregnant, right?” she posits. “So it’s important if folks are seeing any sort of line with their own eyes, faint or otherwise, to respond as if they are positive and take the necessary precautions immediately.”
Getting a faint line result on your test isn’t uncommon, however — both experts and health providers have indicated that the opaqueness of the line on your COVID-19 test may be influenced by an individual’s viral load, or the quality of the sample collected. Meaning, the darkness and rigidity of the positive line result on your test may be linked to how sick you currently are, a single indicator of how you are progressing in a COVID-19 illness (more on that later).
As confusing as it may be, a light positive line is still considered positive; you’ll need to follow the same precautions and care instructions as if your result was clear as day.
What does a COVID-19 home test measure?
Not all rapid home tests are the same. Certain tests measure for specific proteins (known as nucleocapsid proteins) within a sample, markers that are known to be associated with SARS-CoV-2, whereas other tests identify genetic material instead. The liquids used within a COVID-19 test help to extract “viral proteins” from a nasal sample, explains Joseph Mann, MSN, FNP-C, a medical science liaison for health technology provider BD. These proteins are then transferred onto the actual home test receptor.
In that 15-minute window, a chemical reaction takes place — and a result indicates whether these proteins were present in the sample. But those taking multiple rapid COVID-19 tests may not realize that their result windows and the opaqueness of a positive line can often vary depending on a myriad of factors.
“Faint or dark test lines develop on COVID-19 tests for any number of reasons and shouldn’t be used as a predictor of disease severity or virulence,” Mann tells Good Housekeeping. “Slight differences in sample collection, adherence to testing procedures, and other factors can directly impact the strength of the lines.”
Meaning just because you may experience a “light” positive on one test doesn’t mean it will remain that way on subsequent or repeat testing, Mann adds.
What does a faint line on a COVID test mean?
The short answer? Yes. As rapid antigen COVID-19 tests measure the presence of viral proteins, even a faint line positive result indicates that SARS-CoV-2 has had an impact on your immune system. A false positive isn’t as likely as a false negative result on a home test early in a person’s infection, explains Sandra H. Bonat, M.D., a pediatric expert and virologist with VIP StarNetwork, a mobile healthcare provider specializing in COVID-19 support services.
“A faint line on a home COVID test indicates the presence of COVID-19 virus proteins and should be considered a true positive,” Dr. Bonat says. “Since it takes a certain level of virus to cause a positive test, a person should assume they are contagious if they have a positive home test result, even if the line is faint.”
If you’re not currently experiencing any obvious COVID-19 symptoms (like brain fog!), think about your activity over the last few days — have you been traveling? Visiting crowded, indoor spaces? And try to consider the COVID-19 spread around you; officials at the Centers for Disease Control and Prevention (CDC) have released a county-specific spread indicator to help determine risk. More likely than not, a flurry of viral cases in your area should give you more than enough context to realize you are, indeed, sick.
A faint line on a rapid antigen test should prompt you to immediately isolate yourself from anyone in your home, and follow up with your primary healthcare provider as soon as possible for further instructions.
Does a faint line mean you have recovered from COVID-19?
If you’re testing yourself after the bulk of your COVID-19 symptoms has settled, you may be surprised to see a faint line and a positive result given your recent recovery. But you should consider yourself still contagious if you’re testing positive (however faint an indicator may be!) after recovering from COVID-19 symptoms, even if you are outside the five-day minimum isolation window as recommended by the CDC.
“Just as some people will test positive on a home test and remain asymptomatic, some individuals will test positive on a home test after COVID-19 symptoms have subsided,” Dr. Bonat adds. “A faint positive line on a home test after recovering from COVID-19 symptoms is an indication of viral proteins being present — therefore, that person may be still contagious.”
Rapid antigen tests aren’t designed to serve as a diagnostic for how you are currently recovering from COVID-19, adds Dr. Volk, clarifying that the FDA didn’t approve home tests “to measure how far down the recovery path you are” but rather “to determine whether or not COVID is present or absent.” After all, if an individual had fully recovered, they would stop shedding all virus particles traced in nasal swabs, Dr. Volk explains — and a faint line result indicates that this is not the case.
It’s true, theoretically, that individuals are less contagious after they’ve recovered from primary COVID-19 symptoms compared to when they first tested positive. But Dr. Bonat advises continuing to take precautions like wearing well-fitting masks in public and avoiding those who are at elevated risk, in addition to staying home if at all possible, until your home test indicates you are negative — and is free of any faint lines in results.
Zee Krstic is a health editor for Good Housekeeping, where he covers health and nutrition news, decodes diet and fitness trends and reviews the best products in the wellness aisle. Prior to joining GH in 2019, Zee fostered a nutrition background as an editor at Cooking Light and is continually developing his grasp of holistic health through collaboration with leading academic experts and clinical care providers. He has written about food and dining for Time, among other publications.