Tl;dr: Differential diagnosis helps clinicians figure out what questions to ask, makes sure they rule out “can’t miss” diagnoses, and helps them determine what testing and follow-up a patient needs.
If you’ve ever read the note your doctor, PA, or NP wrote about you on your patient portal for an emergency room visit, hospital stay, or even a sick visit, you might notice something a little strange. They rarely say that they are 100% certain that you have one particular illness unless there’s a specific test that says exactly what’s going on (for example, a positive swab for flu or an x-ray showing a broken arm). Even then, you might notice language like “Arm pain most likely due to fracture demonstrated on X-ray.” And you read that and might say, “Well duh, of course someone’s arm hurts because it’s broken.” So why do clinicians have this weird way of describing what could be going on with you? The answer is two words: differential diagnosis.
What is a differential diagnosis?
A differential diagnosis is a list of conditions that could be related to a particular symptom.
Here’s a common example: “A patient presents with a headache.” Before a clinician even sees you, they look at the main complaint (also called a chief complaint) and come up with a list of all the possible things that could cause that headache. For example, the headache could be from something as simple as not drinking enough water, or due to a migraine, or a cluster headache, or a tension headache. Then the clinician has to ensure they think about the more serious conditions, so they’ll add tumors, infections, and brain bleeds to the list.
Before a clinician even sees a patient, they have a list of several things that could be going on. That’s important for a few reasons.
Guiding questions: A broad differential list helps guide the sorts of questions a clinician asks. For the patient with a headache, the clinician is going to want to know the intensity of the headache, if there are triggers, what part of the head hurts, if there have been recent life stressors, just to name a few immediate questions. These questions help the clinician eliminate some diagnoses and push others to the top of the list.
Reducing “anchoring”: Anchoring is when a patient says something and the clinician focuses on that at the expense of other information that could suggest something else. Let’s stay with our headache example. Say our patient has a history of migraines. The clinician might think that it’s a slam dunk, just more migraines. So they prescribe some migraine medication and move on with their day. But if they had asked the patient about other symptoms, they’d have learned that the patient has headaches that are waking them from sleep, and they then immediately vomit. Those symptoms are “red flag” signs for a brain tumor. It’s an extreme example, but it’s important to avoid anchoring because clinicians can miss the actual diagnosis. In medical school, for example, my peers and I are taught to always have a list of “can’t miss” diagnoses for a wide variety of chief complaints.
Broadens or narrows testing: Having a broad differential also helps the clinician figure out what tests to order. We’re going to stick with the headache example from above. If the patient is describing a headache that radiates from the shoulders up to the back of the head, and they’ve had a huge work project this month and have spent hours hunched over a computer, that sounds like a tension headache. A clinician wouldn’t order imaging for that. But for the patient with the horrible headaches that wake them up from sleep, the clinician would order a brain MRI to rule out a potential tumor. With the right questions, clinicians can figure out what tests to order to confirm what’s going on.
What can you do to help your clinician get to the right diagnosis?
- Keep an accurate log of your symptoms, including when the symptoms started and anything else you’ve been experiencing (such as fevers, vomiting etc.).
- Be descriptive in how you talk about your symptoms (for example, if you’re having pain, is it dull and achy or sharp and stabbing. Does the pain radiate anywhere?).
- Know your medical history (any conditions you might have, such as diabetes or hypertension) and any medications you take.
- Be honest about any recent changes in your health history because sometimes the small things are the most important (for example, any recent new supplements, any drug use, any recent travel, any changes in eating habits)
Further Reading:
How can I prepare to get the most out of my next medical appointment?
