When you seek attention for a medical concern, your doctor uses the diagnostic process to determine the condition that may be causing your symptoms.

As part of this process, they’ll review items such as:

A differential diagnosis is a list of possible conditions or diseases that could be causing your symptoms based off of this information.

When performing a differential diagnosis, your doctor will first collect some initial information regarding your symptoms and medical history.

Some example questions your doctor may ask include:

  • What’re your symptoms?
  • How long you have been experiencing these symptoms?
  • Is there anything that triggers your symptoms?
  • Is there anything that makes your symptoms worse or better?
  • Do you have a family history of specific symptoms, conditions, or diseases?
  • Are you currently taking any prescription medications?
  • Do you use tobacco or alcohol? If so, how frequently?
  • Have there been any major events or stressors in your life recently?

Your doctor may then perform some basic physical or laboratory examinations. Some examples include, but are not limited to:

  • taking your blood pressure
  • monitoring your heart rate
  • listening to your lungs as you breathe
  • examining the part of your body that’s bothering you
  • ordering basic laboratory blood or urine tests

When they’ve gathered the relevant facts from your symptoms, medical history, and physical examination, your doctor will make a list of the most likely conditions or diseases that may be causing your symptoms. This is the differential diagnosis.

Your doctor may then perform additional tests or assessments to rule out specific conditions or diseases and reach a final diagnosis.

Here are some simplified examples of what a differential diagnosis may look like for some common conditions.

Chest pain

John visits his doctor complaining of pain in his chest.

Since a heart attack is a common cause of chest pain, his doctor’s first priority is to make sure that John is not experiencing one. Other common causes of chest pain include pain in the chest wall, gastroesophageal reflux disease (GERD), and pericarditis.

The doctor performs an electrocardiogram to evaluate the electrical impulses of John’s heart. They also order blood tests to check for certain enzymes that’re associated with a heart attack. The results from these assessments are normal.

John tells his doctor that his pain feels like a burning sensation. It typically comes shortly after having a meal. In addition to his chest pain, he sometimes has a sour taste in his mouth.

From the description of his symptoms as well as the normal test results, John’s doctor suspects that John may have GERD. The doctor prescribes John a course of proton pump inhibitors that eventually relieves his symptoms.

Headache

Sue goes to see her doctor because she’s having a persistent headache.

In addition to performing a basic physical examination, Sue’s doctor asks about her symptoms. Sue shares that the pain from her headaches is moderate to severe. She sometimes feels nausea and sensitivity to light while they’re occurring.

From the information provided, Sue’s doctor suspects that the most likely conditions could be migraines, tension headaches, or possibly a post-traumatic headache.

The doctor asks a follow-up question: Have you experienced any sort of head injury recently? Sue responds that yes, she had fallen and hit her head a little over a week ago.

With this new information, Sue’s doctor now suspects a post-traumatic headache. The doctor may prescribe pain inhibitors or anti-inflammatory medications for her condition. In addition, the doctor may perform imaging tests such as an MRI or CT scan to rule out bleeding in the brain or a tumor.

Pneumonia

Ali visits his doctor with symptoms of pneumonia: fever, cough, chills, and pains in his chest.

Ali’s doctor performs a physical exam, including listening to his lungs with a stethoscope. They perform a chest X-ray to view his lungs and confirm pneumonia.

Pneumonia has different causes — particularly if it’s bacterial or viral. This can affect treatment.

Ali’s doctor takes a mucus sample to test for the presence of bacteria. It comes back positive, so the doctor prescribes a course of antibiotics to treat the infection.

Hypertension

Raquel is at her doctor’s office for a routine physical. When her doctor takes her blood pressure, the reading is high.

Common causes of hypertension include certain medications, kidney disease, obstructive sleep apnea, and thyroid problems.

High blood pressure doesn’t run in Raquel’s family, although her mother had thyroid problems. Raquel doesn’t use tobacco products and uses alcohol responsibly. Additionally, she’s not currently taking any medications that could lead to high blood pressure.

Raquel’s doctor then asks if she’s noticed anything else that seems out of the ordinary with her health lately. She replies that she feels as if she’s been losing weight and that she often feels hot or sweaty.

The doctor performs laboratory tests to assess kidney and thyroid function.

The kidney test results are normal, but Raquel’s thyroid results indicate hyperthyroidism. Raquel and her doctor begin to discuss treatment options for her overactive thyroid.

Stroke

A family member takes Clarence to receive immediate medical attention because they suspect he’s having a stroke.

Clarence’s symptoms include headache, confusion, loss of coordination, and impaired vision. The family member also lets the doctor know that one of Clarence’s parents had a stroke in the past and that Clarence smokes cigarettes frequently.

From the symptoms and history provided, the doctor strongly suspects a stroke, although low blood glucose can also cause symptoms similar to a stroke.

They perform an echocardiogram to check for an abnormal rhythm that could lead to clots, which could travel to the brain. They also order a CT scan to check for brain hemorrhaging or tissue death. Lastly, they perform blood tests to see the speed at which Clarence’s blood clots and to assess his blood glucose levels.

The CT scan indicates a hemorrhage in the brain, confirming that Clarence has had a hemorrhagic stroke.

Since a stroke is a medical emergency, the doctor may begin emergency treatment before all test results are obtained.

A differential diagnosis is a list of possible conditions or diseases that could be causing your symptoms. It’s based off of the facts obtained from your symptoms, medical history, basic laboratory results, and a physical examination.

After developing a differential diagnosis, your doctor may then perform additional tests to begin to rule out specific conditions or diseases and come to a final diagnosis.