Home pregnancy tests are fast and relatively inexpensive (relative to going to a doctor). A home pregnancy test is an “antigen test.” The antigen in this case is a hormone (HCG) that is excreted in a woman’s urine in the early stages of pregnancy. Urine is applied to a test strip that contains a manufactured antibody* that binds to receptors on the hormone antigen. That antigen-antibody complex triggers a color change in the test strip. It’s fast, simple, and cheap. If one is at all skeptical of the result the test can be repeated easily. Any uncertainty (or a positive result) should trigger a medical visit. [Note: a pregnancy test looks for an antigen, i.e. HCG, using a manufactured antibody. Don’t confuse that with testing for natural antibodies to Covid-19 as a way of telling if a person has been infected. These are two very distinct uses of the word antibody.]
At this time there is no such test for Covid-19, but a fast, cheap, and readily available home-based test for Covid-19 would be a major game changer: it looks like a lot of transmission of Covid-19 occurs from asymptomatic (40% of those infected never have symptoms) and pre-symptomatic (1-2 days before symptoms) people, and from folks who are a little sick, but who convince themselves they’re not sick enough to stay home. That transmission pattern is the single most intractable and troublesome characteristic of this disease.
If, in addition to wearing masks and social distancing, a whole lot of people in the community routinely tested themselves with this (still imaginary) fast, cheap, home test–and then, if it were positive, stayed home pending the result of further testing, we would once again have some control over the spread of Covid-19. Then we could move on to the contract tracing and quarantining that has allowed many other countries to carry on in a manner much closer to normal (and to look at the U.S. in puzzled amazement).
If such a fast and cheap test were broadly available it wouldn’t even need to be highly accurate to help us out as a community. If today’s test missed a few virus particles (a negative result that was false, i.e. a “false negative”), another test later in the week would pick up the virus when it was present in higher quantities. An asymptomatic patient with a large viral load is much more likely to spread the virus than someone whose viral load is barely detectable. Similarly, a false positive result (patient has no virus but the test says they do) one morning is a nuisance, but, if false positives are not too frequent, the ones that dooccur just mean you’re quarantined until subsequent more accurate tests show the true state of affairs.
But no such test is currently available. We have two broad kinds of tests for presence of the virus. (To be distinguished from testing patients for evidence they’ve been infected, i.e. looking for natural antibodies in patients’ blood. These are also called “serology” tests, i.e. tests of blood serum.)
There are two types of tests for presence of the virus. Antigen tests look for viral proteins (instead of viral genetic material) are generally the faster tests, but none is yet available that is home-based, nor that is it sufficiently inexpensive. “Molecular” tests, most of which detect bits and pieces of the viral genetic material, usually involving something called PCR (polymerase chain reaction), a technique that amplifies the minute quantities of the genetic material to make it more detectable. The molecular tests generally require more challenging lab technique (i.e. not practical for home use), and are more expensive. [The “molecular tests” link above is to a Johns Hopkins webpage that offers a lot more detail.]
The test Mr. Trump and his White House staff use to insulate themselves from exposure to Covid-19 (while they tell everyone else to go out and expose themselves to save the economy) is the Abbott rapid ID NOW test. It is a molecular test (for viral genetic material). It requires a small processor console that is certainly beyond the financial reach of most people. Thanks to the opaque medical pricing from which we continue to suffer in the United States, I was unable to learn what one test processed through this machine is likely to cost. For those with a device on site it delivers a result in less than 15 minutes. It has been criticized for failing to detect virus when it is present (false negatives). Nonetheless, it certainly reduces the likelihood that someone spewing virus will enter the White House.
Most molecular tests for Covid-19 require a sample to be delivered to a qualified laboratory for processing. The test result often is not available to the patient for days or even a week. That is no help in determining whether you need to stay home on the day of the test, if there is any time left on the day of the test after you’ve jumped through the hoops necessary to be tested at all. hence, the recommendation to self-quarantine until the result is known and negative.
Antigen tests for Covid-19 proteins (overall much faster than molecular tests, but still requiring a machine) are becoming available, but I could not find a timeline for the development of a home-based test. Somehow, one might imagine that a country that put a man on the moon could figure this out…
None of this is cheap. Trying to learn the cost of a test is a frustrating exercise. Not only are the charges variable for currently available testing, but searching immediately brings up discussion of stock prices of the various companies making the tests. This is U.S. medical non-free market “capitalism” with all its warts. Don’t expect any help from the Trump administration.
Keep to the high ground,
Jerry
*An antibody is an organic (carbon-based) chemical, a specialized protein (made of chains of amino acids), that is produced either by a body’s immune system or chemically manufactured to bind very specifically to a “binding site” on a target protein.
P.S. I cannot think of a medical test that is perfectly sensitive (detects everyone with the disease) and perfectly specific (detects only those actually have the disease). Furthermore, among tests there is often some trade-off between sensitivity and specificity. (If math doesn’t give you hives and you want to look harder at this concept, check out https://kennis-research.shinyapps.io/Bayes-App/ It turns out that a Presbyterian minister, Thomas Bayes, worked out the math back in the 18th century.) This is the stuff that experts actually use to come up with their recommendations. Laboratory scientists and doctors spend their lives quantifying how tests work and what the results mean. It is material that very few reporters and even fewer politicians and political pundits ever understand. All of us tend to think in terms of a test being “positive” or “negative” as the be-all and end-all, black and white result. Like so much of life, it is not that simple.