Because the quality of the diagnostic process is so important in determining the quality of care, addressing gaps in standards, methodology, and funding should be a top concern for policymakers. This article summarises the objectives of diagnostic testing and research, as well as the methodological obstacles and study design alternatives available to researchers.
The system of diagnosis
Aspects of diagnostic studies that are intended to accomplish these goals include the detection or exclusion of disease, assisting in care, assessing prognosis, monitoring clinical courses and measuring general health or fitness.
The “gold standard” problem, spectrum and selection biases, “soft” measures (subjective phenomena), observer variability and bias, complex relationships, clinical impact, sample size, and the rapid advancement of knowledge are all examples of methodological obstacles.
Testing’s goals and objectives
Diagnostic investigations gather information to clarify a patient’s health state by examining personal traits, symptoms, indicators, and history, as well as doing physical examinations, laboratory testing, and utilising extra facilities to collect information from patients. The following are some of the objectives.
In order to increase assurance about the presence or absence of disease, it is necessary to have appropriate discriminatory ability. Measures of discrimination are frequently obtained that compares the outcome of a test to a reference standard, allowing tests to be compared between one another. When it comes to tests for similar purposes, the accuracy, invasiveness, and risk can vary significantly. For example, a history may be no less valuable than laboratory tests in some situations. Additional investigations must contribute important information to less invasive and less expensive tests that were performed earlier in order to be useful.
Supporting clinical management
Determining the presence, location, and shape of arterial lesions, for example, is important in order to make therapeutic decisions for these lesions.
As a beginning point for clinical follow-up and informing patients, determining prognosis is essential.
When an illness is left untreated, or during or after therapy, it is important to monitor the clinical course.
Measuring fitness—for example, in preparation for a sporting activity or for a job.
It is necessary to evaluate tests in line with their stated objectives, while also taking into consideration potential inconveniences and consequences, such as intestinal perforation during an endoscopic procedure. It is therefore necessary to compare the results of using a test vs not using a test, or the results of utilising alternative tests.
The results of an evaluation before a test is introduced into routine care can still be freely compared to determine the effect on prognosis if the test is used or not used. Early evaluation aids in making decisions about whether to launch a test and how to plan for postmarketing surveillance after it is introduced.
Challenges in terms of methodology
Problem with the “gold standard”
When evaluating discriminatory power (accuracy), the outcome of a test is compared with a standard diagnostic that has been established independently of the test. The existence of “gold standards” that provide complete confidence is rare. Even biopsies have the potential to fail in this regard. Generally speaking, the challenge is to develop a standard that is as close as possible to the theoretical gold standard in terms of performance.
An appropriate reference standard may not always be accessible; for example, neither imaging techniques nor biopsies will detect all liver abnormalities when determining the accuracy of liver testing. Furthermore, it is difficult to establish invasive treatments as the gold standard in a research study. When evaluating symptoms that are already incorporated into the description of a condition (as in migraine), or when symptoms are more relevant than anatomical state (as in prostatism), an independent criterion may not even be conceptually possible. When investigating the value of physical examination in detecting severe disease in patients with non-acute abdominal pain, comprehensive screening, including invasive procedures (if ethically permissible), may yield many irrelevant findings while failing to exclude relevant pathology in the majority of patients. The most appropriate clinical follow-up, such as a “delayed type cross sectional study” with a final assessment by independent specialists, is then the most appropriate strategy to take. 1,9
Conclusion
It is possible to develop new diagnostic tests that are superior to the current reference standards. It is possible that new standards will be ignored if research into the accuracy of test procedures is based solely on comparisons with existing standards. This is because they are in conflict with the currently applicable standards. As a result, current pathophysiology expertise is required to be able to update a reference standard when the need arises.