Interpreting Diagnostic Tests

Tim L. Uhl, PhD, ATC, PT, FNATA
- Professor, Department of Physical Therapy
- University of Kentucky, College of Health Sciences, Physical Therapy
Clinical Background
  - Clinical practice since 1985
  - Experience in Sports Medicine Clinics and High School & Collegiate Athletics
  - Past-President of American Society of Shoulder and Elbow Therapists
  - Co-founder of the UK post-professional Athletic Training Graduate Program (1999)
  - Authored ~750 shoulder presentations and publications

First Job: Determine what is wrong with the patient
- Establish a diagnosis/classification
- Utilize provocative (special) testing to provoke symptoms or identify tissue injury

Evaluation: A dynamic process where the therapist makes clinical judgments based on examination data.
- Important for organizing data into defined clusters to guide intervention strategies.
Examination: Process of history taking, system reviews, and administering specific tests to gather relevant data.
Diagnosis: Evaluates information gathered during examination and classifies it into clusters, syndromes, or categories for appropriate intervention.
Prognosis: Predicts the optimal improvement attainable through intervention and time required to reach it.
Outcomes: Results of management include remediation of limitations and optimizing patient satisfaction, in addition to prevention strategies.
Intervention: Involves purposeful interactions with the patient using various physical methods to align with the diagnosis and prognosis.

History:
   - Location
   - Time
   - Characteristics
   - Associated Symptoms
Observation:
   - Posture
   - Functional Movement (Gait, Reaching)
   - Shape
   - Skin
   - Assistive Device
Neurological Assessment:
   - Nerve trunks
   - Reflexes
   - Sensation
   - Motor Function
   - Cranial Functions
Palpation:
   - Skin
   - Muscle
   - Tendon
   - Joint
Range of Motion:
- Active, Passive, Resistive, Traction/Compression, Gliding

Examples of tests in class:
- Painful Arc Sign
- Hawkins-Kennedy Impingement Test

Need for continual education on Diagnostic Accuracy studies
Example study: The Value of Physical Tests for Subacromial Impingement Syndrome
- Published in The Journal of Bone and Joint Surgery
- Discusses diagnostic accuracy for subacromial impingement syndrome

Accurate Diagnosis: Determining interventions based on diagnostic accuracy.
Application of the Best Intervention: Using clinical prediction rules, clinical trials, and case series.
Evaluating Outcomes: Assessment of how well the intervention worked from both therapist and patient's perspective.

Reading Assignment: Study to evaluate accuracy of 2 clinical tests for SLAP Tear
- Tests: Crank Test, Active Compression Test (O’Brien Test)
- Study group: 65 patients (prospective study)

Definition: Superior Labral Anterior-to-Posterior lesion involves glenoid labrum detachment near the biceps anchor.
Descriptive studies categorize it into 4 types based on surgical observations (Snyder, 1990).

Studies on SLAP Tears:
  - Diagnostic accuracy for SLAP tears (Stetson and Templin, Am. J Sports Med, 2002)
  - Clinical trials comparing interventions
  - Current concept articles offering treatment opinions (Level 5 evidence)

Understanding the difference between Sensitivity and Specificity is crucial.
Identification of good Positive (+) and Negative (-) Likelihood Ratios is essential for clinical decision making (Fritz & Wainner, 2001).

Prospective Design: Blind comparison involving clinical tests with a reference standard in a relevant population.
Blinded Comparison: Evaluator doesn't access prior information influencing judgment.
Consecutive Series of Patients: Inclusion of patients continuously over time to promote representativeness.
Relevant Clinical Population: Patients displaying symptoms necessary for differential diagnosis.
Clinical Test Definition: Clear identification and methodology of the tests performed.

A Good Study aims to reduce bias through rigorous design.
Various biases include:
- Spectrum Bias: Ensuring the study represents a range of severity among the conditions examined.
- Selection Bias: Need to accurately define study population and include relevant patients.

A checklist (such as QUADAS 2) can be utilized to assess the design and minimize bias.
Important to verify that the reference standard and outcomes are applied to all patients appropriately.

Validity Assessment: Determining if authors minimized bias through transparent methods.
Interpretation of Results: Understanding sensitivity, specificity, and likelihood ratios is necessary for clinical relevance.
Applicability to Patient Population: Results must be pertinent to those treated in clinical settings.

Defined as a combination of sensitivity and specificity, showing how patient probability changes with test results.
Positive Likelihood Ratio (+LR): Indicates an increased chance of having an injury.
Negative Likelihood Ratio (-LR): Indicates a decreased chance of having the injury.
Threshold for good (+) LR (>10 or 5-10) and (-) LR (<0.1) indicates strong diagnostic utility.

Distinguish between incidence ratios in exposed versus unexposed groups for the likelihood of an event occurring.
Relative Risk Calculation: Ratio of incidence in exposed/unexposed groups helps determine statistical significance and clinical relevance.
Ensuring a confidence interval does not cross 1.0 is crucial for claiming significance in risk.

Merging various tests may provide more diagnostic information than individual tests alone.
Example Criteria for Shoulder Impingement: Recognition of various tests (e.g., Neer test, Hawkins-Kennedy test) offers better diagnostic accuracy than singular testing.

Mastery of diagnostic accuracy studies is fundamental for effective patient management in physical therapy.
Continuous research engagement and critical analysis of existing literature is essential for advancing clinical practice and outcome optimization.