What is a differential diagnosis?

Different health conditions often cause similar symptoms. For example, fatigue is a symptom that can be caused by anemia, depression, heart disease, thyroid disease, sleep disorders, and many other conditions. If you have fatigue or other symptoms that are linked to many conditions, your provider has to figure out which condition you have so that you get the right treatment.

To make a diagnosis, your provider will follow a careful step-by-step process of ruling out conditions that share your symptoms until it's clear which condition is most likely the cause of your illness. This process is called making a differential diagnosis.

An important step in making a differential diagnosis is to make a list of all the possible conditions that you might have. This is your differential diagnosis list. Your provider will base your list on your specific:

• Symptoms
• Medical history
• Family health history
• Test results

A list of possible conditions helps your provider decide which tests will help confirm or rule out the conditions that could be causing your symptoms. Your test results help narrow your differential diagnosis list until it's clear which condition you have. This is your final diagnosis.

The process of making a differential diagnosis may take time, but it helps make sure your provider doesn't miss a possible cause of your symptoms. That means your final diagnosis is more likely to be accurate and you'll get the right treatment.

How is it used?

A differential diagnosis process is used to help make a final diagnosis when you have symptoms that don't have one clear cause. It can be used to help diagnose physical and mental disorders.

What happens during a differential diagnosis?

To make a differential diagnosis, your provider has to think like a detective and follow several steps:

The first step is to gather clues by asking you about your health.

Your provider will ask detailed questions about your:

• Symptoms, such as:
  • How do your symptoms feel and how do they affect you?
  • When did they start and how long do they last?
  • What makes them better or worse?
• Medical history. Your provider will consider whether your symptoms could be related to health problems you already have.
• Medicines and supplements. Sometimes symptoms can be side effects from medicines or supplements, so your provider will want to know about anything you take.
• Family health history. If a certain condition runs in your family, your provider will consider whether your symptoms are a sign of that condition.
• Life and habits. Changes or problems with your sleep, diet, exercise, work, mood, and relationships can be causes or symptoms of many conditions.

The second step of the differential diagnosis process is a physical exam. Information from an exam gives your provider more clues about your health. It may help rule out certain conditions or make others seem more likely.

The third step is to put together a differential diagnosis list. Your provider will come up with a list of "suspects" -- the conditions that you may have based on information about your symptoms, health, and lifestyle.

The fourth step is to order tests. Tests can help confirm or rule out the conditions on your differential diagnosis list. The tests you have will depend on the conditions on your list. If your list includes a serious condition that may need urgent treatment, you'll have tests for that condition first.

Common tests to help narrow your differential diagnosis list may include:

• Lab tests, such as blood and urine (pee) tests
• A biopsy
• Imaging tests, such as an MRI scan, ultrasound, or x-ray
• A mental health screening if your symptoms could be caused by a mental disorder

As test results rule out some of the possible causes of your symptoms, your final diagnosis should become clear. Then your provider can recommend treatment.

What do my results mean?

The conditions on your differential diagnosis list are not your final diagnosis. They're the conditions that could cause symptoms like yours. If you have questions about these conditions, talk with your provider.

Your provider will use the differential diagnosis list to choose which tests to order. Each time you get test results, ask your provider how they affect your differential diagnosis. Test results may help your provider decide to do other tests, or they may guide treatment choices.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a differential diagnosis?

Your provider may recommend starting treatment before your final diagnosis is certain. That's because the goal of making a differential diagnosis is to narrow the possible causes of your symptoms until your provider can figure out which treatments are most likely to help you.

In certain cases, your provider may learn more about your condition by seeing whether or not a treatment improves your symptoms. That information may help lead to a final diagnosis.