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.

When symptoms could have more than one cause, your provider will follow a careful, step-by-step process to rule out conditions that share your symptoms and identify the most likely cause. This process is called making a differential diagnosis.

To make a diagnosis, your provider first creates a list of all the possible conditions that could explain your symptoms. This is your differential diagnosis list. Your provider will base the list on your specific:

• Symptoms
• Medical history
• Family health history
• Medicines and supplements
• Lifestyle
• Test results

A differential diagnosis list helps your provider decide which tests will help confirm or rule out some of the possible conditions. As test findings narrow down the list, the most likely condition will become clear. 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:

• Mental disorders.
• Neurological conditions.
• Infections.
• Hormonal or metabolic conditions.
• Autoimmune diseases.

Differential diagnosis is especially useful when symptoms overlap across many conditions, such as fatigue, headaches, chest pain, shortness of breath, dizziness, or unexplained weight changes.

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. Your provider may want to know what symptoms you have, how long you've had them, what makes them better or worse, and how they affect you.
• Medical history. Your provider will consider whether your symptoms could be related to health problems you already have. They may also ask if you've ever experienced your current symptoms before.
• Medicines and supplements. Sometimes symptoms can be side effects from medicines or supplements, so your provider will want to know about everything 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.
• Lifestyle and habits. Changes or problems with your sleep, diet, exercise, work, mood, and relationships can be causes or symptoms of many conditions. So, to help narrow the differential diagnosis list, your provider may ask you if there have been any changes in your life.

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 make a list of possible conditions ("suspects") 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 are only the conditions that could be causing your symptoms. If, for example, you have abdominal (belly) pain, then your differential diagnosis list may include conditions such as:

• Appendicitis.
• Gastritis.
• Inflammatory bowel disease.
• Intestinal or bowel blockage.
• Pancreatitis.

Your provider will then 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:

• Narrow the list.
• Rule out certain conditions.
• Suggest additional tests.
• Point toward a likely diagnosis.
• Guide early treatment choices.

If you have questions about the conditions in your differential diagnosis list, talk with your provider.

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. This usually happens when:

• A condition on your list needs urgent treatment.
• Your symptoms are severe.
• Starting treatment could help clarify the diagnosis.

In certain cases, your provider may learn more about your condition by seeing whether a treatment improves your symptoms. This approach can be especially useful for gastrointestinal disorders and autoimmune diseases.

If you have questions about your diagnosis or next steps, talk with your provider.