Can PCR And Rapid Tests Both Be Wrong? Dr. Mallika Marshall Answers Your COVID Questions
BOSTON (CBS) — Dr. Mallika Marshall is answering your coronavirus vaccine-related medical questions. If you have a question, email her or message her on Facebook or Twitter.
Dr. Mallika is offering her best advice, but as always, consult your personal doctor before making any decisions about your personal health.
Katie on Facebook asks, "Is it possible for both PCR and rapid tests to be wrong? I have symptoms and keep testing negative even though everyone else in the house is asymptomatic and positive."
PCR tests are pretty accurate, assuming the clinician got a good sample. If multiple PCR tests are negative, perhaps you have another virus or allergies or another condition that mimics COVID. Or perhaps you tested too early. You should test five days after your exposure, but it may take up to 10 days for you to develop symptoms, so you may need to continue to test until that time.
Bette writes on Facebook, "I'm wondering if COVID rapid test kits have expiration dates?"
Yes, rapid antigen tests do have expiration dates, usually 6 to 12 months after production, and using a test beyond that date could lead to faulty results. That said, some manufacturers have extended their expiration dates, so check online or call the company if you're wondering if your test has expired. This is also a good reminder that it doesn't make sense to stockpile tests that could expire before you get a chance to use them.
Also on Facebook, Wendy asks, "How long should an N95 mask be worn? We go into a store twice a week for 25 to 45 minutes at a time."
You can wear an N95, KN95, or KF94 as long as you need to do so. I wear an N95 at work for up to 6 hours at a time, which is long. It's not comfortable, but I can get my work done safely. I go to a safe area or outside to take breaks when I need to. And as long as the mask doesn't get soiled or wet, you can reuse it for some time.
And Rob from Natick writes, "I just bought some KN95 masks but read online that they should be discarded after 5 years. Why is this necessary?"
Apparently, it's not the mask itself that can degrade over time, but the elastic bands which can become damaged by sunlight, heat or cold and lose their ability to provide a good seal. So it's probably best to store your masks in a dark, dry, room temperature location. I keep mine in a wooden box in the family room.
