Making a diagnosis

Making a diagnosis can be difficult. It is especially difficult in primary care.

Within primary care, conditions will often be seen at an evolutionary stage when the characteristics of symptoms are changing; with time, the patient will have had additional time to reflect on his/her story and the symptoms may have become more clear.

Diagnostic uncertainty is inherent in the practice of medicine. Patients often present with undifferentiated symptoms that change over time, making it difficult for clinicians to identify a satisfactory explanation of the patient’s presenting problem. In addition to patient presentation, time constraints of the patient-clinician encounter, complexity of medical science and limitations of diagnostic tests all influence diagnostic decisions in the midst of uncertainty. Described as analogous to looking for a snowball in a blizzard, diagnostic decision-making under uncertainty is challenging for clinicians and must be appropriately managed in medical practice.

Medical diagnosis is the process of determining which disease or condition explains a person’s symptoms and signs. The information required for diagnosis is typically collected from a history and physical examination of the person seeking medical care.

One of the main purposes of diagnosis is to guide treatment planning.

The steps of the diagnostic process fall into three main categories: Diagnostic assessment – patient history; physical exam; evaluation of the patient’s chief complaint and symptoms, leading to a differential diagnosis and after that the ordering of diagnostic tests.

A differential diagnosis means that there is more than one possibility for the patient’s diagnosis. The doctor must differentiate between these to determine the actual diagnosis and appropriate treatment plan, according to the “moment” of the clinical picture that the patient presents with. Medical decisions are the acts that convert information into action.

Doctors will give a provisional diagnosis when they are not 100% sure of a diagnosis because they need more information. Essentially, based on the information they have, they are making an educated guess about the most likely diagnosis.

Diagnostic error can be defined as a diagnosis that was missed, wrong or delayed, as detected by subsequent definitive tests or findings.

The “basic science” of diagnostic uncertainty is poorly understood.

Diagnostic uncertainty is dynamic and changes with time.

For a patient presenting early in the course of disease (with undifferentiated symptoms), a clinician might have considerable uncertainty, that may resolve with time as details evolve.

Uncertainty encompasses three principles: probability, ambiguity and complexity.

Three types of decisions arise in the clinical management of patients: evaluation of signs and symptoms to make a diagnosis; decisions about the need for additional tests to refine a diagnosis; and the choice of a treatment.

These decisions occur each time a physician sees a new patient, and smaller versions of these decisions can reocur many times in the course of managing a single patient. Every time a new symptom or sign develops, or a new test result is received, the physician must interpret the new information and determine the underlying problem.

The medical diagnostic problem is similar to many diagnostic problems that arise in everyday life. It involves uncertainty and decision; however, the medical diagnostic problem has a degree of complexity that makes it different.

First, there are hundreds, even thousands of different diseases that can cause signs and symptoms.

Second, each disease can cause many different signs and symptoms.

Third, the signs and symptoms of various diseases overlap; most of them can be caused by more than one disease.

Fourth, the relationships between diseases and signs and symptoms are uncertain. For every disease and every sign or symptom, there is a probability each sign or symptom will occur with that disease, creating thousands of probabilistic relationships.

Fifth, most of the probabilities are only roughly known.

After evaluating a patient’s signs and symptoms, the physician may be uncertain about which disease the patient has and may have a list of possibilities.

Diagnostic uncertainty can be defined as a “subjective perception of an inability to provide an accurate explanation of the patient’s health problem”.

The clinician does not need to be absolutely certain about the diagnosis to initiate treatment, but rather needs to reduce the level of diagnostic uncertainty below a certain threshold to narrow options to certain conditions.

Most of the clinical problems encountered in everyday general practice can be dealt with effectively, on the basis of a good clinical history. But patients vary in their ability to recall symptoms.

Making a diagnosis in primary care can be perplexing. Symptoms are not synonymous with organic disease and when seeking to make a diagnostic decision there is a need to consider symptoms in the context and from the perspective of the patient.

As it has been said before, we need to know what sort of patient has a disease, more than what sort of disease a patient has.

Whilst a good physician treats the disease; the great physician treats the patient who has the disease.

Diagnosis is not easy, as doctors are not given divinatory capacities when they graduate.

Some do have a special gift, a feeling that when grounded in a good strong state of the art knowledge is a fantastic asset.

This is why Medicine is not only a science but also an art.

Best health wishes,
Maria Alice

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Dr Maria Alice is a consultant in General and Family Medicine. General Manager/Medical Director – Luzdoc International Medical Service. Medical Director – Grupo Hospital Particular do Algarve/ Hospital S. Gonçalo de Lagos