In the emergency department, I’ve often had patients who come in telling me what they think is wrong with them. They will often start with “I know my own body”. Or, painfully (for me), they will tell me that they looked it up on Google, know what they have, and request a specific treatment.
Now, first, understand that I do appreciate people do know themselves and often have greater understanding of their specific instance of a long-standing chronic disease. However, doctors are trained to think in a very particular, thorough, way in order to ensure that nothing is missed. Or, with even potentially worse outcomes, nothing is done to the patient that will harm them and not help them in any way.
Second, I have experience that people can be both right, and very wrong, about what they think is wrong with them. They can also be very right, or very wrong, about what they need. In either case, whether they are right or wrong, I am responsible for taking appropriate care of them and, like any doctor; I want to take care of my patients in the best way possible.
One of the first things we learn early in medical school is that patients will actually give us the diagnosis, through their history – what the patients tell us and the answers to our questions – about 90% of the time. This is important to understand, because often I am asked by patients why I am not doing any testing or a specific test. The truth is, the only purpose of testing is to either rule in, or rule out, diagnoses I am considering based on the history and physical exam. It is rare for any doctor to be surprised by something found on diagnostic testing.
The reason is rare for us to be surprised by a diagnoses is we are taught to do something called the differential diagnosis. For any given complaint, whether it is abdominal pain, chest pain, cough or fever, every doctor has a list of potential causes inside their head. As we obtain history from a patient we are constantly rifling through those “differentials” and deciding whether they apply. As we listen to the patient, and ask questions, moving some diagnoses up higher in the probability list, some differentials lower and eliminating other differentials entirely. For example, simply by reason of being male, I can rule out an ectopic pregnancy (pregnancy outside the uterus) in a male patient complaining of abdominal pain.
Once I have fixed a differential diagnosis in my mind, I then order a set of tests which will help me either rule in, or rule out that diagnosis. Another misconception most people have about these tests are that they give simple “yes” or “no” answers. Honestly, this is never the case. Every single test, whether it is a lab test to look at blood cells or a CT scan to look at abdominal pain, has a “specificity” and “sensitivity”. Most simply put, sensitivity is a measure of how likely the test is to pick somebody up with a given disease. Specificity is a measure of how likely it is that without the disease will come up with a positive test. So, for example if I do a test on 100 people with a specific disease, a test with 97% sensitivity (considered quite good), would pick up 97 of those 100 people. Three, however, would show up as negative with that test—even though they actually do have the disease. Specificity is different, if I do a test on 100 people none of them have the disease, a test with 90% specificity (also considered fairly good), it would show 10 people have the disease that do not. If you put these two numbers together, actually multiply one times the other, you get a positive predictive value of the test. So if I have a test with those two numbers 97% specificity and 90% sensitivity the positive predictive value would be 87%.
However, this is the point at which it gets tricky. Against that positive predictive value, a doctor also has to measure their clinical suspicion that the patient actually has the disease. So, for example, if I have a patient come in with a classical history for appendicitis, and elevated white blood cell count, a fever, loss of appetite in a clearly convincing exam and the CT of the abdomen comes up negative, there is actually still a very good chance that the patient has appendicitis. A CT done early in the course of appendicitis can be negative. In these cases my clinical training tells me that I need to have that patient come back in about 8 to 12 hours and repeat the exam, and possibly the CT.
However, what about the other side of it? What if somebody comes in with a vague history which doesn’t really give me much of an idea what they’ve got and I order random tests to try to figure it out. Unfortunately my low clinical suspicion combined with a low positive predictive value, means that when I do those random test they are essentially useless for telling me whether or not somebody has the disease. Essentially I multiply my clinical suspicion of the disease process, based on history and exam as well as other tests I may have already done, if my initial clinical suspicion is less than 3% even a test with positive predictive value of 87% still really comes out to a less than 1% chance the patient has the disease.
So, why not just order scattershot tests to “figure things out”? Essentially, we don’t do that, because of our oath to “do no harm”. The problem is that there is not a single test in medicine that does not have some attached risk. “What?” You ask, “How can this be? Surely an EKG or a blood test isn’t dangerous!”
Well, as it happens, they can be. If you remember earlier in the article I talked about sensitivity and specificity, this is where the danger to excessive unnecessary testing comes in. Let’s say a patient comes in with a complaint of a headache. I do my standard history; figure out that it’s most likely a tension headache, resolves easily with Tylenol and ibuprofen. There’s absolutely nothing dangerous about this headache at all based on history. The patient wants a CT of the head. I’m a nice doctor, I don’t want to argue with them about it and maybe they have some suspicion that there something wrong. I order the CT of the head.
Say the CT head comes back with something abnormal, we’re not quite sure what, so we send the patient to a neurosurgeon. The neurosurgeon, wanting to be sure there something there worth looking at does an MRI of the brain. MRI shows that was just an artifact on the CT, but there’s another area that looks suspicious. The neurosurgeon decides to do a biopsy. This area is located in an important part of the brain for communication. The neurosurgeon performs the biopsy – and no matter what you may have heard, neurosurgery is not particularly delicate – and there’s some injury to the speech area of the brain. But, the biopsy comes up negative. This is how a CT of the brain actually harmed the patient. Here is a news article that explains it more thoroughly.
Because of the possibility of harm resulting from testing, the question we frequently ask ourselves is, “will the outcome of this test affect management?” This means that if we do a test and it’s for nothing more than our curiosity, or defensive medicine, then it is probably not worth doing the test. If, on the other hand, a negative or positive result will cause us to change what we are doing for the patient, then it is worth doing the test. Of course, as I say this, I feel compelled to admit that in the emergency department we do a fair amount more scattershot testing than in any other specialty, just based on the risks of people coming into the emergency department being more likely to have life-threatening emergency, and not having a great deal of time to figure it out.
So, to sum up, doctors think this way: first we get a history, we make a list of possible differential diagnoses then we do physical examination to see if we can rule out or in any of those diagnoses. If we still have anything remaining, that we’re not pretty certain about, we can then perform testing to further rule in or rule out possible causes of the symptoms. We base our final diagnosis upon both our clinical judgment and experience, many years of education, as well as careful interpretation of the tests we perform. We try not to perform tests that will not affect the eventual treatment of the patient. When the result of those tests don’t make sense in the context of the patient in front of us, we will often repeat the tests or have the patient return in a period of time so we can reevaluate them.
Physicians strive not to harm their patients, whether through missing diagnoses or through doing unnecessary testing, but of course both we and the patient are human. Humans are complex, squishy, and often contradictory. Also, they don’t always tell us the truth or even really understand what we think the truth is in the context of their illness. So, if you ever get a diagnosis from a physician, even me, that you think is suspect or needs further inquiry, ask! if you don’t understand what is being done to you, and why, it shouldn’t be done until you do.
Of course, all of this is much easier to achieve for both doctor and patient in a direct primary care practice. You can always find your closest direct primary care practice at DPCfrontier.com. Or, if you like, call or e-mail me and I will help you find the nearest DPC doctor! Doctors are quitting insurance-based practices every day and starting new direct primary care practices, so even if there wasn’t one near you a year ago, there may be one now!
As always if you have any questions please feel free to call me at 760-425-4466 or email me at Dr Edwards@wowhealingcare.com.
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