Diagnosis and prognosis can be scary words—and confusing ones. But once you understand the difference, they can actually provide reassurance. That’s because one is an explanation of what exactly is wrong and one is a prediction of how things will turn out.
In this article, we’ll examine the difference between a diagnosis and a prognosis in medicine as well as in general use.
⚡ Quick summary
When a doctor tells you what specific disease or condition is affecting you, that’s a diagnosis. When they tell you how that disease or condition is going to affect you—how long you’ll be sick or whether you’re likely to fully recover—that’s a prognosis. In general usage, diagnosis refers to an assessment of what the problem is with something, while prognosis can refer to any prediction.
What does diagnosis mean?
In medicine, a diagnosis is a medical professional’s determination of what disease, disorder, or condition is affecting a patient. A diagnosis usually involves research done on the patient, such as physical examinations or medical tests. The word can refer to both the process of making the determination and the conclusion of that process. Either way, the result is identifying the specific cause of your illness.
The plural form is diagnoses, pronounced [ dahy-uhg-noh-seez ]. The verb form is diagnose. A doctor can be said to diagnose an illness or a patient but the meaning is the same—to diagnose is to give a diagnosis of what specific condition is affecting the patient. The adjective form is diagnostic, as in diagnostic tests.
Outside of medicine, diagnosis is used more generally to refer to any analysis or examination of a problem (and sometimes to the proposed solution). Its verb and adjective forms are also used generally in this way.
What does prognosis mean?
In medicine, a prognosis is a prediction of how a disease is likely to affect a patient. The term is especially used in the context of more serious illnesses and conditions (such as cancer) to refer to a prediction of how likely or unlikely a patient is to recover.
The plural form is prognoses, pronounced [ prog-noh-seez ]. The verb and adjective forms (prognose and prognostic) are not commonly used.
Outside of medicine, the word prognosis is used more generally to refer to any prediction or forecast of the future, as in Her prognosis for our fourth quarter earnings is bleak.
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diagnosis vs. prognosis
Medically, diagnosis and prognosis are often used in the same context, but they refer to different types of assessments. A diagnosis comes before a prognosis.
Once a diagnosis is made about what specific disease or condition is affecting a person, a doctor can deliver a prognosis—a prediction about the course or outcome of the disease or condition. In other words, a diagnosis is a determination of what is affecting a patient, while a prognosis is a prediction of how it will affect them.
A diagnosis is typically based on observation of symptoms and diagnostic testing. A prognosis is based on the patient’s specific circumstances and what’s known about how the diagnosed condition typically affects patients in similar circumstances.
Both diagnosis and prognosis are also used generally. In general usage, the word diagnosis refers to a determination about what the problem is with something, such as a machine or a process. In contrast, a prognosis is a prediction about how something will turn out. For example, in business, the diagnosis of poor earnings may be that demand for the product has fallen, while the prognosis may be that earnings are likely to continue to decrease.
In casual use, diagnosis and prognosis are sometimes used interchangeably to refer to assessments, predictions, or guesses. But in medicine, the distinction is important.
Medical diagnosis and prognosis examples
Case 1: A patient complains of nausea and pain in their abdomen. After performing a thorough examination and tests, the doctor gives the diagnosis: the patient has appendicitis.
The doctor says that the patient will need an appendectomy. Based on the examination, testing, the patient’s specific circumstances, and what’s known about the risks of the procedure, the doctor gives the prognosis: the patient is likely to fully recover if the surgery is successful and there are no complications.
Case 2: A tumor is discovered during an examination. After additional testing, the doctor gives a diagnosis: the tumor is cancerous. However, it is determined that the cancer is still in the early stages and the tumor can be removed, likely without any serious consequences. Based on all the facts of the case, the prognosis is that the patient is likely to fully recover due to low risk of further spread.
In this case and in many others, a prognosis is likely to be repeatedly updated as an illness progresses or recovery is monitored. Remember, a prognosis is just a prediction—bodies and illnesses are often unpredictable and a prognosis may change as circumstances change.
