In the process of making a correct diagnosis we want to make sure patients do not have other disease(s) by excluding specific diagnostic possibilities. This is in part done by ordering diagnostic tests. The results of such testing are said to rule in or rule out diagnoses. A simple example of this is a patient who shows up to a doctor with chest pain. Diagnostic testing in the form of an electrocardiogram (EKG-and electrical map of how the heart is working) and laboratory tests that are indicative of a heart attack are obtained and depending on the results of this testing, the patient is said to either rule in for a heart attack if the tests are positive or rule out if the tests are negative. Obviously, in the case of a patient with chest pain, it is very important to diagnose a heart attack and it is just as important to make sure a patient with chest pain is not having a heart attack. This paradigm of either ruling in or ruling out diagnostic possibilities has become a strong tenet in medicine.
There is obvious utility in this process. It is reassuring to patients, families and health care providers to make sure someone does not have some god awful diagnosis and, god forbid, if they do, it is important to know this. It is also imperative to obtain as much of a definitive diagnosis as possible in order to treat a patient. There is a lot of emphasis on diagnostic testing in medicine both on the part of practitioners and health care consumers.
This all would be straight forward if ruling in or out a particular diagnosis was a sure thing; if this testing as part of the diagnostic process was perfect. If the elevation of cardiac enzymes and a positive EKG meant 100% that the patient was having a myocardial infarction. But nearly all diagnostic testing is imperfect and has pitfalls. What is more, a positive test or finding in one patient may be unimportant or mean something else in another. And most times, it is just not one or a few diagnostic tests that are run, but many with the idea ruling out many possible diagnoses. This shot gun approach is the norm rather than the exception.
It is typical for a patient presenting to an emergency department with symptoms of chest pain or shortness of breath to have a myriad of diagnostic tests ranging from ones for the evaluation for a heart attack to a tests for blood clots in the legs or lungs. These tests could include an electrocardiogram, a chest x-ray, possible Doppler Ultrasound studies of the veins of the legs, and a spiral CT scan of the chest-the last two looking for the aforementioned blood clots. Additionally, blood work would entail a complete blood count which may show anemia (low blood) or an increase in the white blood cell count possibly indicating an infection like pneumonia. Electrolytes looking at sodium, potassium, chloride, bicarbonate, and glucose in the blood, along with blood work indicative of kidney function will be routinely ordered. An arterial blood gas may be obtained looking blood pH, and the concentrations of carbon dioxide and oxygen in the blood along with another blood test, if elevated, that would be supportive of heart failure (BNP-brain natriuretic peptide). Tests of liver blood tests and of the how the blood clotting system working may also be ordered.
What may seem at the surface and initially to be a logical, straight forward and streamlined process becomes very complicated. As in the above example, there can be many diagnostic tests generating numerous data points each of which have to be accounted for and interpreted in the context of a single patient encounter. And some of these tests are not simply just positive or negative but involve interpreting multiple findings over a broad range of possibilities as is the case with interpreting chest x-rays or EKGs. Given all of this, some of this data will be normal and some maybe abnormal. Some of what is abnormal may be important and some may be of little or no importance. And of course, these same principles apply to the normal data as well: some of it important and some of it no so important. What the clinician must do is to figure out what is important and what is not. In borrowing from engineering terminology, a clinician must figure out what is signal (important) and what is noise (not important). It gets even trickier because the noise can interfere with the signal; that is, what is unimportant or extraneous can get in the way of what is important. The noise can muck up the signal.
I have left out until now the whole part of getting a history from the patient and performing a physical exam. This is the starting point for diagnosing and treating patients and so should guide the ordering all of those diagnostic tests but this too, not surprisingly, can get lost in all the noise. And we are not done yet. Multiply this by factors ranging from 8 to 20 that make up the number of patients that can be in a busy emergency department or intensive care unit. Mix in multiple health care providers from nurses, to medical students, to residents and fellows, to attending physicians from multiple specialties all running around trying to figure what is important and what is not. Spice it up with health care providers having differing opinions on the best way to diagnose and treat a given patient assuming that they have some semblance of knowledge as to what is actually going on. Throw in pressures to get patients in and out; the tight constraints placed upon health care providers to be time-efficient, cost-saving conscious while at the same time trying to provide the best and most thorough care. Top all this off with the emotional stress of being a patient or health care provider in such an environment; the din of what is important can easily be lost in a sea of cacophony.
There are numerous other factors I have not mentioned that make all this a lot more complicated and add even more noise. Like life, all this is… well…very, very complicated. So, where do we go from here as patients and care providers? Maybe start at the beginning with the patient showing up and the clinician taking the time to get a detailed history and perform a careful physical examination. This is going back to what all those sage and masterful clinicians had been telling us doctor types in medical school and throughout all the years of our subsequent training: that everything in this process starts with the history and physical.
This may seem simple and obvious but in reality it can be quite challenging. Again, getting those patients in and out and those tight time pressures clinicians face in caring for patients. It may seem easier for a busy and overwhelmed clinician to briefly speak to a patient, do a cursory physical exam, and just check off a bunch of tests on a lab order sheet and then go on to the next patient. We’ll just sort everything out when all those tests come back. This is the shot gun approach and it does not work well.
By proceeding based on a careful history and physical and upon knowledge and experience, a clinician will form a working diagnosis and order testing based on what is carefully thought out to be going on with the patient. This can do more than cut down on the on all the noise but greatly improve the diagnostic precision of testing. The patient can also be started on treatment. As the data comes rolling in, the clinician will have a clear idea about what to do with the results. If the results of testing does not fit well with the working diagnosis, than a re-evaluation can be made and additional testing and treatment can be initiated or changed. Further support of a diagnosis is made if the patient is responding favorably to treatment targeting the working diagnosis.
An important point that is sometimes lost is that tests do not diagnosis disease, people (clinicians) do. All this testing is part of, and an extension of the history and physical. This is about choosing thoughtfully and carefully what to ask for and about fitting data from tests and procedures with the history and physical to form a complete a picture of what is going on with the patient. This is really what being a good clinician is about and aside from doing right by the patients, it can also be immensely gratifying when everything comes together.