What is a Diagnosis?

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Diagnosis in healthcare is among the most important processes since the protocol for patient treatment depends on this step. Even more, health research and policy draw on this area for their validity. For instance, payment policy, allocation of financial and other resources, and research focus are determined largely by diagnoses.

Woman being diagnosed by doctor

Image Credit: Portrait Image Asia/Shutterstock.com

Diagnosis depends on a framework of clinical reasoning, or what is termed clinical decision-making. It has been described as a "pre-existing set of categories agreed upon by the medical profession to designate a specific condition."

The importance of diagnosis in patient care is dependent on its accuracy, reliability, and timeliness, all of which make key contributions to the health outcome. The importance of diagnosis is only highlighted in the case of infectious disease since undiagnosed patients can spread the infection to others.

The diagnostic process

Diagnosis is the endpoint of a complex process centered on a patient, collaborating with both the patient and other sources of clinical information to reason backward as to the potential health issue causing the patient's current condition.

Typically prompted by symptoms, the patient first engages with the healthcare system. This leads to one or more rounds of gathering, integrating, and interpreting information, ultimately arriving at a working diagnosis. Information may enter this loop at various times, altering the earlier hypothesis as other probabilities arise or are strengthened.

Communication is key during this process, both between the patient, family members, and healthcare professionals.

Sources of information include:

  • The clinical history
  • Physical examination
  • Diagnostic testing
  • Consultation with other clinicians

Arriving at a diagnosis involves ruling out differential diagnoses. Once a working diagnosis is arrived at, the patient should be informed, including how reliable to diagnosis is.

All further changes in the diagnosis must also be shared with the patient, especially as the diagnosis is modified and refined with further incorporation of data. Finally, when one or at most two possibilities are left, the working diagnosis is verified. This refers to comparing the diagnosis with the various signs and symptoms, evaluating how well it fits the patient's risk factors and state of health, and the need for additional diagnoses to explain the clinical features.

The importance of diagnostic verification lies in proceeding with only those tests that are justified by the expected information obtained and its positive impact on patient outcomes. Sometimes, risky or invasive tests are required for diagnosis when the information available is inadequate to explain the health issue or belies the working diagnosis.

Patient treatment precedes the arrival at a final diagnosis, as it should, but further care can be optimized by continuing to make sure that the uncertainty surrounding the working diagnosis is being progressively reduced with each step. The outcome of the initial or provisional treatment itself provides important information that can refine the working diagnosis.

Bedside evaluation

History taking is a skill that is fundamental to diagnosis and building a relationship with the patient. It is linked to interviewing the patient, where the clinician obtains the patient's medical history, or previously acquired details of history are verified to be accurate.

Various types of clinical history include the current or presenting symptom, the past medical history, family history, social history, drug and medication history, and supplement history. A good history is based on communication, which requires rapport, good manners, and time. This is followed by a physical examination, which can help determine the next diagnostic step, including diagnostic testing, and build further trust.

Diagnostic testing

Testing became key to diagnosis only about a century ago. Testing may occur through multiple rounds and sometimes pick up potentially dangerous conditions before they become apparent. Diagnostic testing uses laboratory tests, pathology, and imaging, in addition to mental health screening tests, sleep apnea tests, and tests for vision, hearing, cognition, and neurological status.

Clinical decision-making

Clinical reasoning involves putting the information together to assess and manage the patient's medical issues. Both analytical and non-analytical methods of decision making are involved, the one being rapid, unconscious, and intuitive but the other slow, deliberate and reflective.

Many biases can affect the accuracy of such thinking. These include dependence on mental shortcuts, or heuristics, which can fail, called a cognitive bias. This is the tendency to think in a way that causes poor judgment. It can also be caused by variations in effect, tiredness, distraction, and physician motivation. Overconfidence, attributing physical symptoms to known mental illness, and relying on typical symptoms, can cause misdiagnosis.

With experience and typical symptoms and signs, analytical thinking takes a backseat to automatic processing. For instance, experienced doctors use pattern recognition to diagnose illnesses because they rapidly generate multiple mental models of diseases and match them to their observations. Feedback mechanisms are key to improving diagnostic accuracy, as a result. The use of information technology properly can lead to better clinical reasoning but can also reduce its quality.

How to make a clinical diagnosis: a step by step guide

Challenges to diagnosis

The sheer volume and pace of diagnostic technology advancement have left doctors and other clinicians behind since they are only human. This could be addressed by sharing patient care by teams of healthcare professionals, broadening the pool of expertise and resources while splitting the responsibility to stay up to date with the latest evidence.

Systematic reviews and best practice guidelines are invaluable in this aspect of medical care. Guidelines are, however, difficult to apply in individual cases and lack enough strong evidence.



Last Updated: Sep 1, 2021

Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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  1. Chris Carvalho Chris Carvalho Brazil says:

    What is it named when you have 15 min consulting with a MD that don't make a clinical history, don't make laboratory tests, just do average physical exams, don't believe in the symptoms of the patient, don't consult colleagues, and finally make a "diagnosis" of "myelin disease plus overlapping syndrome", and don't give any treatment?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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