San Antonio Express-News (Sunday)
Are at-home COVID-19 tests reliable?
Q: How reliable are home COVID-19 tests? I’ve read one article that said that if you tested negative you could be certain that you did not have COVID-19, but if you tested positive there was a significant chance of a false positive. Another article said exactly the opposite. What are the facts?
A: You’re asking about how accurate the home tests are. There are two primary measures of tests: the sensitivity and the specificity.
Sensitivity is the probability that a given test will detect the condition, if it’s there. For at-home COVID-19 tests, the sensitivity has been reported to be between 79 percent and 95 percent. However, how the sample is collected can affect the sensitivity, and the realworld performance may not be quite as good as what the manufacturers report. Timing is also important, and the optimum time for testing is probably three to five days after an exposure. The test is most likely to be positive just before and just after a person begins having symptoms.
The specificity is the probability that the person really has the condition when the test is positive. At-home tests generally perform well, with reported specificity ranging from 92 percent to 99 percent.
So, the tests can give both false positives and false negatives. A negative test is only somewhat reassuring: I have had several patients have negative at-home tests but positive in-hospital PCR tests. However, the specificity is high: If you test positive, the likelihood is high that you really have COVID-19.
One important point, though: Test results need to be interpreted within a person’s context. If you were exposed to a person known to be contagious with COVID-19 and now have fever and cough, a positive test result is virtually certain to mean you have COVID-19. However, if you have had no exposures, and have been sitting at home not seeing anybody, and you take a test that comes out positive, that’s almost certain to be a false positive.
The calculation of the positive predictive value — when the test result is positive, do
you really have COVID-19? — relates to both the likelihood you had COVID-19 before knowing the test results and the test characteristics. The same is true of the negative predictive value, i.e., if the test is negative, are you really free from COVID-19? Your doctor can help you interpret the results for your specific situation.
Q: I used to give whole blood two to five times a year, but several years ago I went on meds for an enlarged prostate and was told by the Red Cross that they could not use my blood due to the risk of birth defects if a pregnant woman received blood containing finasteride.
Aren’t platelet donations washed? Could I donate platelets?
A: In general, the requirements for donating platelets are the same as for donating blood. That means you should wait a month after taking finasteride before donating blood or platelets.
I had another reader in the same situation ask whether his blood could just be given only to men; again, the blood banks want maximum safety and flexibility in giving blood products.
Q: I’m 71 and have had both
Moderna COVID-19 vaccination shots. When I called my doctor to inquire about a Moderna booster, I was told one was not available now but that I could take the Pfizer booster. Can you confirm this? I’m a little wary of taking another type of booster shot.
A: The immunity to COVID-19 from the Moderna mRNA vaccines seems to be a bit longerlasting than that for the Pfizer vaccine, and as of this writing, a third dose of either Moderna or Pfizer vaccine is recommended only for people over 65 or who are otherwise at high risk or with frequent institutional or occupational exposure.
Some research has been done on changing the type of vaccine for an individual, and the results are promising that there might be additional benefit to changing. However, the Food and Drug Administration recently advised that any approved COVID-19 vaccine (Pfizer, Moderna or Janssen) may be used. All three provide high protection with low risk.
I am putting some of the newest recommendations on my Facebook page for those who want more detail, facebook.com/drkeithroach.
Q: I am an 88-year-old man. I drool 24/7. Your recent column
did not offer a solution. I heard of a drug called hyoscyamine. It is a travel sickness drug, but also is used for drooling. Any ideas if this is effective for drooling?
A: Drooling can have many causes, and a careful evaluation of any abnormalities in neurological function, dental problems or sinus and nasal inflammation may lead to a specific treatment. When no specific cause can be identified, medications to reduce saliva production can be tried.
Physicians take advantage of the side effect of dry mouth to reduce drooling. In addition to the hyoscyamine, other medications used include: atropine eyedrops under the tongue; the antidepressant amitriptyline; and glycopyrrolate. All have been used successfully. These medications are not usually completely effective but can often help. Care must be taken not to dry the mouth out too much, as this can accelerate dental disease.
For some people, chewing gum or hard candy can encourage swallowing and help with drooling, especially in social situations. In severe cases, botulinum toxin can be injected into the salivary gland.
Q: My husband and I both take atorvastatin (10 mg for
me, 20 mg for him). Should we be taking CoQ10? Your recent column suggested that atorvastatin depletes CoQ10? We are 79 and 81 years of age.
A: I don’t recommend CoQ10 supplementation to people who have no noticeable side effects from their statin drug, of any type or dose. In many people who notice symptoms they attribute to the statin, such as muscle or joint aches, the symptoms are not due to the statin.
Studies done on prevention of side effects by CoQ10 have failed to show a benefit. However, if a person does have a muscle symptom that seemed to have started at the same time as the statin, the CoQ10 can resolve the symptom in about a third of people (which is about the same as the benefit in the placebo group).
Since CoQ10 is safe and relatively inexpensive, about $10 per month for a well-known brand, it is reasonable to try to see if it helps.
Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell .edu or send mail to 628 Virginia Dr., Orlando, FL 32803.