A word about medical tests. In light of the coronavirus pandemic, you have probably seen me on Facebook telling people not to worry about getting the test. Clearly, I must be mad. Clearly this must be some kind of evil plan to capitalize off of sick people. Let me explain myself.
It is not uncommon for the lay public to think a medical test will have one of two outcomes; the patient has the disease and the test indicates they have the disease or the patient does not have the disease and the test indicates that the patient does not have the disease. In an ideal world, all medical tests would be that good. But guess what? There’s not a single medical test on the planet that does this. Not a single one.
In fact, a medical test is going to have one of four outcomes not two. Here are the four possible outcomes: Either
1) The person has the disease and the test indicates that the person has the disease.
2) The patient has the disease, but the test indicates that they do not. This is a false negative.
3) The patient does not have the disease and the test indicates that the patient does not have the disease. Or,
4) The patient does not have the disease, but the test indicates that the patient does. This is a false positive.
Every single test that we have at our disposal in medicine has false negatives and false positives. As a practitioner of medicine I have to know the characteristics of the test that I am using. But let’s back up a second. How would I know the test for disease is giving false results? I need a second “More accurate” test to determine that the disease is actually present in those for whom my test is falsely negative. This second test acts as a gold standard to which the first is compared.
Here’s an example. Let’s talk about pneumonia. If you come in to see me and you tell me that you’re coughing, you have a fever, and you’re getting green mucus. Then, I listen to your lungs and I hear abnormal sounds in one area of your lungs. I could diagnose you with pneumonia. But, “wait a second” you’re saying. “Don’t I need a chest x-ray?” Well the answer to that is “no”…unless I think that there is an alternative diagnosis that has to be ruled in or out. Or maybe I just want to be extra sure because of the implications of the treatment that I will be prescribing. So let’s say you do get that x-ray and it shows pneumonia in the place where I already knew you had pneumonia. That would be the gold standard for pneumonia. I don’t need to apply the gold standard to everybody with pneumonia because literally millions of such X-Rays have confirmed this clinical presentation time and time again.
With that in mind let’s move forward. So we use a gold standard to determine what we called the sensitivity and the specificity of a test. Sometimes that gold standard is something as simple as a chest x-ray… Historically the gold standard was the autopsy. Now the autopsy won’t always tell you what somebody had but it will definitely always give you the prognosis 100% of the time. In fact, the autopsy is the only test in medicine that has 100% of anything and that is its prognostic value. After an autopsy no matter what I find… Your prognosis is that you’re dead. That you were dead was generally an assumption, within acceptable accuracy standards, made before the autopsy…but is without a doubt 100% certain afterwards.
But I digress. So any test is going to have true positives true negatives false positives and false negatives. And we will determine this by measuring against a gold standard. Sensitivity is the measure of how well the test detects the disease in the presence of the disease. Specificity is how well it detects the absence of disease in the true absence of disease. Us medical people go to school a long time to understand this concept and its application to all the tests we do in medicine. See…we’re not just people who wear white coats and don’t do what you want.
The coronavirus test has about a 30% false negative rate. What that means is if you get a coronavirus test that comes back negative there’s still a 30% chance that you have coronavirus. Needless to say, that’s pretty useless information isn’t it? If you have a positive coronavirus test, then you most definitely have the disease. So if you get a coronavirus test that has a 30% false negative, what can you do with the results? If it comes back positive you can quarantine yourself. If it comes back negative… You’re going to quarantine yourself. If you don’t get a test at all… You’re going to quarantine yourself. So clearly for patients who do not need mechanical ventilation, there’s truly no benefit to the test.
Now, what about the people who do need to be hospitalized with coronavirus. Same situation; if I do the test and its positive, then you definitely have coronavirus. If I do the test and it’s negative, there is still a 30% chance that you have coronavirus. The treatment will not change one bit. You’re still going to get mechanical ventilation. You still might get hydroxychloroquine and azithromycin. But the test is completely unnecessary in this scenario…and, quite frankly, takes too much time to be relied upon to decide to initiate any therapy.
Now the forthcoming antibody test? That I think has tremendous value for you as an individual. If you test positive for antibodies to coronavirus you are definitely safer out there in the world than you were if you don’t have antibodies to coronavirus. That’s an actual useful test that will have impact on you.
The coronavirus test itself is not that useful for you as an individual. It’s incredibly useful as a surveillance tool and epidemiological tool. I’ve heard friends tell me that they’ve been exposed to somebody and their work won’t allow them to come back until that person’s test comes back negative. This employer doesn’t understand the test. My assumption would be that they’re trying to prevent the spread of coronavirus but their methodology is horribly flawed and is going to ultimately yield the opposite result. So if they have restrictions on who can come to work they need to base it on something else. Most places base it on whether or not you’re symptomatic. Now of course we all know that that’s not perfect, that plenty of asymptomatic people have the disease and can spread it. But there’s literally no way other than shutting down completely to prevent that. And guess what most businesses are doing… They’re shutting down.
In summation… Don’t worry about the coronavirus test. it’s not going to change much for you if anything. When the antibody test is available, get it. Stay home, stay safe. Protect your healthcare workers by staying home. Come to the ER if you have an emergency situation, but simple cold symptoms (cough, fever, aches) can all be taken care of at home the exact same way we will take care of it in the ER: Tylenol, fluids, rest. Try a tele-medicine service. This is as good a time as any to try this out.
Disclaimer: The opinions stated herein are my own and not representative of any organizations to which I belong.
One thought on “Coronavirus: Don’t Worry About the Test”
Thank you for taking the time to explain this. With so much information out there it’s becoming hard to know what to believe. We appreciate all you do, Dr Franklin! Thank you again and we pray you stay healthy.