Chapter 5: Appraising Diagnostic Research Studies

Pre-Test

1. How does the appraisal process change when considering diagnostic research in comparison with intervention research?

2. What are typical study designs for diagnostic research?

3. What impact might a false-positive test result have on your clinical decision?

4. What would be the clinical application of a negative likelihood ratio?

Introduction

The Diagnostic Process in Physical Therapy

The physical therapy diagnostic process includes patient history, systems review, and informed use of tests and measures. This chapter focuses on the processes of appraising the diagnostic literature of tests and measures and the clinical application of diagnostic research results (Fig. 5.1). Understanding evidence regarding diagnostic tests and integrating diagnostic test results, clinical experience, and patient goals are essential to best practice. Communicating results of the diagnostic process to patients and other professionals requires thorough knowledge of valid and reliable diagnostic tests and the correct interpretation of those tests.

Physical therapists examine patients and evaluate the results of the examination, yielding a diagnosis, plan of care, and likely prognosis.¹ The diagnostic process in physical therapy has been discussed and debated in the literature.^2,3,4,5,6 When you engage in the diagnostic process, you are determining appropriate (if any) physical therapy interventions and any need for referral to another professional. With direct access to physical therapy comes increased professional responsibility. Part of this responsibility is accurate diagnosis of conditions within the scope of physical therapy practice and appropriate referral to other professionals.

Prior to direct access, physical therapists may have relied on a prescription or referral from a physician. Physician referrals continue as the primary referral source for physical therapists, but the majority of these referrals have nonspecific diagnoses.⁷ For example, a referral may be written as "elbow pain," "improve aerobic capacity," or "post-stroke," without a diagnosis concerning the purported etiology of the problem or its relation to movement. It is the physical therapist's responsibility to correctly diagnose the movement problem and determine the appropriate intervention, possible prognosis, and, if necessary, referral to other professionals.

A fundamental tenet of any diagnostic test used in physical therapy is that it can distinguish between people who have a movement disorder and people who do not. Although this sounds obvious, it is more complex.

If you have a sore throat, your physician may use a rapid antigen throat culture for the streptococcal bacteria to diagnose a strep infection. You most likely assume that the results of this test determine that you either have a strep throat or you do not. However, every diagnostic test has a range of values that is positive and a range of values that is negative. This quick test for strep throat detects ...