Differential Diagnosis: Definition, History, Specific Methods, Help of Artificial Intelligence and Uses Outside of Medicine

In medicine, it refers to distinguishing a disease or condition particular from others with similar clinical characteristics.

Physicians and other trained medical professionals use differential diagnostic procedures to diagnose the specific disease in a patient or, at least, to eliminate any imminent, life-threatening condition.

Frequently, each option of a possible disease is called a differential diagnosis (for example, acute bronchitis could be a differential diagnosis in evaluating a cough that ends with a final diagnosis of the common cold).

More generally, a differential diagnostic procedure is a method of systematic diagnosis used to identify the presence of a disease entity in which multiple alternatives are possible.

This method is essentially a process of elimination or at least a process of obtaining information that reduces the “probabilities” of the conditions of the candidate to insignificant levels.

Through the use of evidence such as symptoms, patient history, and medical knowledge to adjust epistemic confidences in the mind of the diagnostician (or, for computer-assisted or computer-aided diagnosis, the system software).

The differential diagnosis can be considered to implement aspects of the hypothetico-deductive method. The potential presence of diseases or candidate conditions can be seen as hypotheses that doctors also determine true or false.


Standard abbreviations of the term “differential diagnosis” include DDx, ddx, DD, D / Dx, ΔΔ, or ΔΔχ.

General components

A differential diagnosis of standard care has four steps. Patient safety requires that the doctor:

  • Gather all the information about the patient and create a list of symptoms. The list can be written in the mind or memory of the doctor as long as the list is made.
  • List all possible causes (candidate conditions) for the symptoms. Again, the doctor can write this mentally, but it should be done.
  • Prioritize the list by placing the most urgent possible causes at the top of the list.
  • Discard or treat the possible causes, starting with the most urgent condition and working on the rest of the list, and discarding practical means of testing and other scientific methods to determine that a state has a clinically insignificant probability of being the cause.

If there is no diagnosis, the doctor made an error, or the condition is not documented. The doctor eliminates the diagnoses from the list by observing and applying tests that produce different results, depending on the correct diagnosis.


Diagnosis is the identification of the nature and cause of a particular phenomenon. The diagnosis is used in many disciplines with logic, analysis, and experience variations to determine “cause and effect.”

It is generally used to determine the causes of symptoms, mitigations, and solutions in systems and computer engineering.

Specific methods

There are several methods for differential diagnostic procedures and several variants among them.

In addition, a differential diagnostic procedure can be used concomitantly or with protocols, guides, or other diagnostic procedures (such as pattern recognition or the use of medical algorithms).

For example, there may not be enough time to make detailed calculations or estimates of different probabilities in case of a medical emergency. The VRC protocol (airway, breathing, and circulation) may be more appropriate.

Later, a complete differential diagnostic procedure can be adopted when the situation is less acute.

The differential diagnosis procedure can be simplified if a “pathognomonic” sign or symptom is found (in which case it is almost sure that the objective condition is present) or in the absence of a sine qua non sign or symptom (in which case it is virtually sure that the aim condition is absent).

A diagnostician can be selective, first considering those disorders that are more likely (a probabilistic approach), more serious if they are not diagnosed and not treated (a predictive system), or more receptive to treatment if offered (a pragmatic approach).

Since the subjective probability of the presence of a condition is never exactly 100% or 0%, the differential diagnostic procedure may aim to specify these various probabilities to form indications for further action.

The following are two differential diagnosis methods based on epidemiology and likelihood ratios, respectively.

A method based on epidemiology

One method to perform a differential diagnosis by epidemiology is to estimate the probability of each candidate condition by comparing its chances of having occurred in the first place in the individual.

It is based on probabilities related to both presentation (as well as pain) and the chances of the candidate’s various conditions (such as illness).

Coverage of candidate conditions

The validity of both the initial estimate of probabilities by epidemiology and the likelihood analysis depends on the inclusion of candidate conditions responsible for most of the likelihood of developing the state. It is clinically significant to include them.

The relatively rapid onset of therapy is most likely to result in the most significant benefit.

No differential diagnostic method will provide the correct conclusion if a critical candidate condition is forgotten.

The need to find more candidate conditions for inclusion increases with the increase in the severity of the presentation itself.

For example, suppose the single presentation is a deviant laboratory parameter, and all common harmful underlying conditions have been ruled out. It may be acceptable to stop finding more candidate conditions, but this would be much more likely to be unacceptable if the presentation had been severe pain.


Suppose two conditions obtain high probabilities after the test, especially if the sum of the possibilities for diseases with known probability ratios becomes more significant than 100%. In that case, the actual condition is a combination of both.

In such cases, that combined condition can be added to the list of candidate conditions, and the calculations should start from the beginning.

Using an initial epidemiology method, the incidence of parathyroid carcinoma is estimated at approximately 1 in 6 million people per year, which gives a very low probability before taking any test under consideration.

In comparison, the likelihood that a non-malignant primary hyperparathyroidismoccurred at the same time as an unrelated noncarcinogenic cancer that occurs with malignant cells in the parathyroid gland is calculated by multiplying the probabilities of the two.

However, the resulting probability is much less than 1 in 6 million. Therefore, the likelihood of parathyroid carcinoma can be close to 100% after histopathological examination despite the low probability that it will occur in the first place.

Finally, let’s say that the diagnosis of parathyroid carcinoma gave rise to a prolonged surgery that eliminated the remaining malignant tissue before it had metastasized, and the patient lived happily ever after.

Differential diagnosis by artificial intelligence

The machine differential diagnosis uses software to perform a full or partial differential diagnosis. It can be considered an artificial intelligence application.

Many studies show an improvement in the quality of care and reducing medical errors through such decision support systems.

These systems are designed for specific medical problems, such as schizophrenia, Lyme disease, or pneumonia.

Others, such as ESAGIL, Iliad, QMR, DiagnosisPro, VisualDx, ZeroMD, DxMate, Symptoma, and Physician Cognition, cover all the main clinical and diagnostic areas to help physicians with a faster and more accurate diagnosis.

However, all these tools still require advanced medical skills to qualify the symptoms and choose additional tests to deduce the probabilities of different diagnoses.

Therefore, non-professionals should still see a health care provider for an adequate diagnosis.


The differential diagnosis method was first suggested for use in the diagnosis of mental disorders by Emil Kraepelin. It is more systematic than the outdated method of diagnosis by Gestalt therapy.

Alternative medical meanings

The “differential diagnosis” is also used more loosely to refer to the most common causes of a given symptom to a list of disorders similar to a given condition.

These lists, when annotated with advice on how to reduce the list (the book ” Differential diagnosis index of France, “ISBN 0-340-81047-5, is an example). Therefore, a differential diagnosis in this sense is medical information specially organized to aid in the diagnosis.

Uses outside of medicine

Biological taxonomists also use methods similar to differential diagnostic processes in medicine to identify and classify living and extinct organisms.

For example, after finding an unknown species, there may be a list of all potential species, followed by discarding one by one until, optimally, only one possible option remains.

Similar procedures can be used by plant and maintenance engineers and automotive mechanics to diagnose defective electronic circuits.