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A provider discusses information with the parent of a young patient

The difference between diagnosis and prognosis

08/12/25
Identifying the medical issue (diagnosis) is the first step toward getting the right treatment. Predicting the outcomes (prognosis) is the next step. Healthcare teams make diagnoses and prognoses based on evidence, such as physical exams and rigorous testing.

Medical terminology can be confusing at first, especially for those managing a new health issue.

For example, physicians sometimes use the words “diagnosis” and “prognosis” when they’re talking about an injury, disease or condition.

These words might sound similar, but they mean different things.

In simple terms, a diagnosis is the process of identifying a health issue. A prognosis is a prediction based on evidence about how the health issue may affect the individual over time.

Here’s how the process works in more detail, with examples and answers to frequently asked questions.

Diagnosis vs. prognosis

Here’s what to know about diagnosis and prognosis.

What is a diagnosis?

A diagnosis is the process of identifying a person’s injury, disease or condition. In other words, it’s the way physicians determine the cause of a health issue.

The medical profession has agreed-upon definitions of injuries, diseases and conditions, so when a physician is determining a diagnosis, they’re narrowing down which ones the person might have based on these established criteria.

To do this, they’ll look at the evidence, which could include:

  • The person’s medical history
  • Blood tests
  • Physical exam
  • Imaging tests
  • Biopsies

For example, a physician may diagnose melanoma if:

  • The person has skin changes that suggest melanoma, like changes in the size, shape, color and feel of a mole.
  • A skin biopsy sample contains cancer cells, which the lab finds meet the criteria for melanoma.

What is a prognosis?

A prognosis is an evidence-based prediction of the outcome of an injury, disease, or condition. It may also include a prediction about a person’s chances of recovery.

Physicians make a prognosis based on factors that affect the outcome of the disease or condition, such as the subtype of the disease and the areas of the body it’s affecting, and the person’s age, sex, overall health, and how well they respond to treatment and cope with side effects.

The more complex the situation, such as when there are medical complications, the harder it is for physicians to make a prognosis with certainty.

Testing is an important part of determining a prognosis. It helps physicians gather detailed information about medical issues, identify how early or late a person may be in disease progression, and recommend the most effective treatments for each person.

How to cope with a diagnosis

People who have received a serious or end stage diagnosis are facing an understandably difficult situation.

A major hurdle that some people face after receiving a diagnosis of a chronic condition is managing the uncertainty that comes with it.

Here are a few ways to manage emotions and expectations after a diagnosis:

  • Speak with a therapist: A therapist or counselor with experience in chronic conditions can provide informed support.
  • Remove unnecessary stressors: Lower stress as much as possible by decreasing or postponing commitments that add to stress and aren’t critical.
  • Get empowered with knowledge: Make a list of health questions about next steps and ask the provider for specific ways to optimize health moving forward.
  • Make healthy choices: Eating healthy, engaging in regular physical activity, taking medications as prescribed, and nurturing supportive social connections are all things within a person’s control that can improve their mood and potentially their medical outcomes.
  • Practice self-compassion: Emotional ups and downs with feelings of anger, guilt, shame and grief are all typical responses after receiving a serious diagnosis. Accepting and processing these emotions rather than suppressing or denying them can help ease them over time.
  • Take one step at a time: Thinking about living with a diagnosis can be overwhelming. It can help to remember to take one small step at a time.
  • Make the most of each day: Worrying about a diagnosis can cause stress. No matter the diagnosis, it can help to practice gratitude. This means taking time to appreciate the good things in life, no matter how small.

Frequently asked questions

Here are answers to some common questions about diagnosis vs. prognosis.

Can a diagnosis change?

Yes, a diagnosis can change as a physician gathers more information about a person’s condition. This information can come from diagnostic testing, consulting with other medical specialists and other methods.

Making a diagnosis is an ongoing process — healthcare teams continually collect new information and reassess the person’s treatment and other needs over time.

It’s also typical for diseases, injuries and medical conditions to change over time.

However, physicians can start treatment even if they’re uncertain about a diagnosis or believe the treatment can benefit the individual based on their current knowledge.

Can a prognosis change?

Yes, a prognosis can change. A disease doesn’t always affect people in the ways physicians expect it to. This is true for cancer and any other health issue.

The best way for someone to find out whether their prognosis has changed is to ask their provider.

Diagnosis and prognosis in cancer: How does it work?

A physician will investigate whether someone has cancer if they describe characteristic symptoms or if test results suggest it.

Then, they will collect more information to make a diagnosis.

There’s no single test to diagnose cancer, so physicians typically use a combination of investigations and tests to get a clearer picture, such as a physical exam, lab tests, imaging tests and biopsies.

If the tests show cancer is present, then the person will likely go through more tests to help their healthcare team decide what treatments to use. At this point, they’re looking to find out:

  • Whether the cancer has spread and where in the body
  • The cancer stage
  • The cancer grade, in some cancers
  • The person’s risk group
  • Whether other markers are present, depending on the type of cancer

Once the physician has more detailed information, they can make a prognosis.

The physician will give the person information about how their cancer may affect them over time, which may include how serious the cancer is, details about treatment and the chances of survival.

Many people find it helpful to know their prognosis and understand the meaning of the survival statistics.

It’s important to know that the prognosis is a prediction based on evidence, but every person is different. That means that sometimes, outcomes may differ from what the physician predicts.

Takeaway

Diagnosis and prognosis are common words physicians use when treating an injury, condition or disease. They sound similar, but they refer to different parts of the medical process.

Diagnosis is the process of identifying a medical issue, and prognosis is an evidence-based prediction of a person’s outcomes.

Both require the healthcare team to gather evidence from sources such as patient reports, physical examinations and diagnostic tests.

A diagnosis and prognosis can change over time, depending on how well a person is responding to treatment and other factors.

Feeling overwhelmed or upset after a serious diagnosis is not unusual. It can help to use coping strategies like speaking with a therapist, removing unnecessary stressors and being kind to oneself.

At Crystal Run, cancer care is a multidisciplinary team approach. Patients receive coordinated care from oncologists/hematologists, certified oncology nurses, an oncology surgeon and a nutritionist. We also make it easy to schedule lab work, diagnostic hematology/oncology testing and biopsies, because we know that comfort, convenience and peace of mind are key. That’s why Crystal Run’s on-site infusion suites were designed with the comfort and privacy of our patients in mind. Crystal Run Healthcare was one of the first 16 community cancer care facilities in America certified by the Quality Oncology Practice Initiative (QOPI®). This important certification demonstrates the ongoing commitment of our physicians, nurses, and support staff to make a difference in the lives of our cancer patients by achieving the highest standards of excellence for their care.