Diagnostic reliability refers to the measure of how accurate symptoms and test results can be in the identification of disease. Some conditions are very easy to diagnose because they have a clear cause which makes it possible to definitively test for them; if a doctor wants to know if a patient has a yeast infection, for example, a culture can be taken from the site and studied in a lab. Other conditions, particularly in psychiatry, are more complex, and are not as easily diagnosed.
Knowing how reliable diagnoses are can be extremely helpful for medical providers making and reviewing diagnostic information. In a situation where the diagnostic reliability is high, they can be confident about a conclusion reached on the basis of the patient’s symptoms, including results of any examination and testing. If it is low or not known, the situation becomes more complicated and the medical practitioner might consider reevaluating the patient. This can be especially important when false diagnosis is a known problem.
One way to determine diagnostic reliability is to run a large study using a big sampling of patients. For privacy and accuracy, this information is typically screened to conceal identifying information. Clinicians can review patient information, including stated symptoms, test results, and other materials. They independently determine if the patients have diagnoses and what they are, and the study coordinators compare the results. This is known as interrater agreement.
If a patient with a specific set of symptoms is diagnosed with the same condition by all the raters, this is an indicator of high diagnostic reliability. If the raters disagree or come up with slightly varying diagnoses, like related psychiatric disorders, it is an indicator of less diagnostic reliability. Information from such studies can also help researchers better define the symptoms and test results that lead to a diagnosis, to increase the chances that specific conditions will be accurately identified.
Awareness of diagnostic reliability can be helpful for patients, especially when they experience what is known as “diagnosis drift.” Some mental health conditions and neurological disorders can have rather vague definitions, and different doctors may have differing diagnoses for the same patient. A patient’s diagnosis might also shift over time with the emergence of new symptoms that provide additional insight. This doesn’t mean one doctor is wrong and the other is right, but is a reminder that diagnostic reliability can be difficult with some conditions because of their complexity and the lack of a definitive cause.