Disclaimer-I have no financial interest or incentive to offer any of the testing listed below. Let me just start out by saying it is far from perfect, can be misleading and is being done at inadequate levels. There are actually two types of testing available:
- PCR testing which tests for SARS-CoV-2 (COVID-19) RNA which is the genetic material found in the virus and is equivalent to viral presence. PCR is short for RT-PCR or real- time reverse transcription polymerase chain reaction. It tests for the viral RNA in upper and lower respiratory specimens to include nasal, nasopharyngeal (deep inside the nose), oropharyngeal (throat), saliva, sputum, lower respiratory tract aspirates, bronchoalveolar lavage done at the time of bronchoscopy and nasopharyngeal wash/aspirate or nasal aspirate done on an individual.
- Antibody testing which tests for immunoglobulins of the M (IgM) and/or G (IgG) class found in blood serum and which are present after infection with the COVID-19 virus. The IgM antibody is seen early on in an infection and it is ultimately replaced by IgG antibodies. It is the IgG class of antibody (immunoglobulin) that can provide protection from subsequent infections from the virus it was informed in response to. Notice that I used the word cannot will.
This is the test you saw on TV here a swab is stuck up the nose or into the back of the throat and is now being replaced by a saliva test. This is not a blood test. Positive tests are correlated with the presence of COVID-19 in the location tested. A positive test result does not exclude a bacterial infection, nor does it exclude co-infection with another virus. A negative result DOES NOT PRECLUDE COVID-19 infection. How accurate is this test? In order to discuss this, it is important to understand the statistical concept of sensitivity. Sensitivity refers to how likely a test will detect what it is looking for so 100% is good, 50% is a coin toss and 0% is bad. PCR testing done on specimens from known COVID-19 infected individuals hospitalized in China were positive in 93% of bronchoalveolar lavage fluid, 92% with sputum, 63% with nasal swabs, 46% with bronchoscopic brush biopsy, 32% with pharyngeal (throat) swabs, 29% in feces and 1% in blood. Another way of looking at this limited data is that the best test looking for COVID-19 viral activity misses 7-8% of known infected individuals (bronchoalveolar lavage or sputum) and the swab up the nose or to the back of the throat can miss 37% to 68% of infected individuals. Testing more than one site improves accuracy which is why in the beginning testing was done through the nose and mouth. THERE IS NO 100% SENSITIVE LOCATION TO TEST WITH PCR. It appears that the PCR test is highly specific for COVID-19 which means that a positive test is detecting COVID-19 and not something else. This test is qualitative in nature which means it does not tell how much virus is present and thus does not convey the likelihood or lack thereof that a positive individual will be more or less contagious.
SEROLOGY or ANTIBODY TESTING
This is a blood test which detects antibodies to COVID-19. There are three possible types of antibodies IgM, IgA, IgG or total antibodies that can be tested for. Early research studies suggest that the majority of infected patients show antibodies between 7 and 11 days after exposure to the virus. Thus, antibody testing is of no value in diagnosing the initial phase of infection. Because COVID-19 is a novel infection it has not been around long enough for us to know how long the antibodies will last and whether or not they will be protective against future infections. We also do not know what percent of infected individuals will test positive for antibodies and even less about what testing for antibodies looks like in asymptomatically infected people. There is no current data defining the sensitivity or specificity of this serologic testing to date. The specificity may be a particular problem with this type of test meaning do antibodies to COVID-19 only show up after a COVID-19 infection or could they appear in individuals who have been infected in the past by one of the more common corona viruses just not COVID-19. Maybe someone can help me out with understanding what a positive or negative antibody test for COVID-19 today means. I certainly do not know. (See below for a math problem to further explain.) A quick internet search for local COVID-19 antibody testing shows it is available to anyone who wants it and has $200 (Manhattan Beach), $125 (Culver City) or $50(Palos Verdes). I will say it again-until we understand this test (actually tests-there are many brands) better it is worthless to the individual. This will certainly change as experience is gained but if you want to feel good take your money and help someone out who can’t afford rent or groceries or healthcare. I know we are all anxious about this pandemic and all of the unknowns associated with it. Once more is known we will be better able to care for ourselves and others and hopefully less anxious. Paying for something that in my opinion has little or no value beyond allaying anxiety is understandable if you do not know what you are or are not getting for your dollar. Those who are offering to take your money should explain what you are getting in return and at least give you the opportunity to seek value.
Assumption-10% of people are or have been infected by the COVID-19 virus. That means that out of 100 people 10 should have a positive antibody test. Assumption-the antibody test is 60% sensitive. That means out of 10 people who have had COVID-19 infection and receive an antibody test 6 would have a positive test and 4 would not test positive (false negative).
Assumption-the antibody test is 80% specific. That means out of the 6 who test positive 4 would be certain to be due to COVID-19 the other 2 not sure. COIN TOSS. Will only cost you $200, $125 or $50 depending on where you live and how far you are willing to drive to toss that coin. Perhaps someone wants to do the second math problem that is defining which test is being done in the locations noted above and what the actual cost is and how much profit is being made and how much value is being received. I hope the math changes and we all get better value for our dollar soon.