How do I interpret these medical test results?

Interpreting Medical Test Results: A Systematic Approach

The interpretation of any medical test result requires integration with clinical context, understanding of test-specific limitations, and awareness of pre-test probability to avoid false conclusions from statistically abnormal findings.

General Principles for Test Interpretation

Context is Critical

• Never interpret test results in isolation – abnormal results outside normative ranges do not always represent disease and must be evaluated alongside clinical presentation, physical examination findings, and other supplementary data 1.
• Determine your pre-test clinical suspicion (high, intermediate, or low) based on patient history, symptoms, and basic evaluation before ordering tests 2.
• The positive predictive value of any test varies dramatically with clinical suspicion: in high-suspicion cases (80% disease prevalence), a positive test has ~97% PPV, while in intermediate-suspicion cases (50% prevalence), PPV drops to ~90% 2.

Quality Assessment First

• Always verify test quality before interpretation – poor quality specimens or technical issues invalidate results 1.
• Check that tests were performed according to manufacturer specifications and that quality metrics were met 1.
• For imaging studies, assess scan quality, presence of artifacts, motion, or technical limitations that could produce false results 1.

Specific Test Interpretation Strategies

Laboratory Tests

Blood Tests (CBC, Chemistry)

• Use laboratory-specific reference ranges, as these vary between institutions 3.
• Serial measurements are more valuable than isolated results – trends matter more than single values 3.
• Consider pre-analytical factors: time of collection, hydration status, recent medications, and intercurrent illnesses all affect results 3.
• Calculate absolute values when interpreting differentials (multiply percentage by total count) 3.

Specialized Antibody Testing (e.g., MOG-IgG)

• Serum is the specimen of choice; CSF testing is rarely needed unless specific circumstances exist 1.
• Document the immunoglobulin class detected, assay type, antigenic substrate, biomaterial used, titer/concentration, assay-specific cut-offs, and performing laboratory 1.
• If "red flags" are present with positive results, re-test the sample using a methodologically different assay to avoid reproducing false-positives inherent to the original method 1.
• Timing matters: antibody concentrations depend on disease activity (higher during acute attacks) and treatment status (lower on immunosuppression, may vanish after plasma exchange) 1.
• If initial testing is negative but clinical suspicion remains high, re-test during acute attacks, treatment-free intervals, or 1-3 months after plasma exchange 1.

Urine Studies

• Urine cytology and markers (NMP22®, BTA stat®, UroVysion® FISH) lack sufficient reliability for routine use due to high false-positive rates (sensitivities 0-100%, specificities 62-100%) 1.
• However, in high-risk patients (irritative voiding symptoms, tobacco use, chemical exposures), cytology may be useful as an adjunct – though negative cytology does not preclude full work-up 1.
• The emotional burden and risks of unnecessary procedures from false-positives outweigh benefits in routine screening 1.

Imaging Studies

Structural Imaging (CT, MRI, Ultrasound)

• Non-contrast CT provides more diagnostic certainty than ultrasound for most applications 1.
• When contrast is contraindicated or advanced imaging unavailable, combine basic imaging with additional procedures (e.g., retrograde pyelograms with ultrasound) 1.
• For pregnant patients, use only ultrasound or MRI to avoid radiation exposure 1.

Quantitative Imaging (OCT, CSLO, Polarimetry)

• Abnormal results (outside normative range) do not always represent disease – criteria for normative databases vary between devices 1.
• Evaluate all components of the report, not just summary statistics, after confirming adequate scan quality 1.
• Individual findings may not fit normative databases for reasons other than disease 1.
• These devices are similar in distinguishing disease from controls but should supplement, not replace, clinical examination 1.

Functional Imaging (Stress Tests, Nuclear Imaging)

• Inconclusive results occur from motion artifacts, attenuation defects, arrhythmias, poor windows, or failure to achieve adequate heart rate 1.
• Results should not be interpreted dichotomously – lower values correlate with more severe ischemia even above cutpoints 1.
• Normal stress imaging does not rule out disease in non-infarct-related territories 1.

Non-Invasive Tests (NITs) for Liver Disease

FIB-4 Score Interpretation

• FIB-4 <1.3 has high negative predictive value for advanced fibrosis – repeat annually in high-risk populations (type 2 diabetes) and every 2 years in low-risk populations 1.
• FIB-4 >2.67 suggests advanced fibrosis; >3.25 suggests cirrhosis (high specificity, low sensitivity) 1.
• Intermediate FIB-4 (1.3-2.67) requires sequential testing with VCTE or other modalities 1.

Vibration-Controlled Transient Elastography (VCTE)

• Requires ≥10 validated measurements with interquartile range <30% of median and success rate >60% 1.
• False-positives occur within 3 hours of oral intake – repeat during fasting state to validate elevated liver stiffness measurements 1.
• LSM >12 kPa is high-sensitivity threshold for cirrhosis but has low positive predictive value (0.34-0.71) 1.
• LSM 8-12 kPa in intermediate FIB-4 patients suggests clinically significant fibrosis 1.

Common Pitfalls to Avoid

The "Abnormal Result" Trap

• Statistical abnormality ≠ clinical disease – many healthy individuals fall outside reference ranges 1.
• Falsely concluding that statistically abnormal imaging represents true disease is a major error – always correlate with clinical findings 1.

The "Normal Result" Trap

• Normal results do not exclude disease when clinical suspicion is high 1, 2.
• Some patients show functional decline without corresponding structural changes on testing 1.
• Negative screening tests in high-risk patients may require repeat testing or alternative diagnostic approaches 1.

Test Degeneracy from Poor History

• Vague complaints that translate into multiple possible symptom interpretations diminish diagnostic test value 4.
• Help patients phrase complaints to limit possible interpretations – this increases post-test probability and reduces unnecessary testing 4.

Qualifying Conditions

• Questions with appended conditions ("What is X, given Y?") are often unanswerable with standard resources 5.
• Rephrase complex questions into simpler components and search clinically-oriented resources 5.

Documentation Requirements

• Report all data using standardized terminology with reference ranges 3.
• Include assay-specific details: method, antigenic substrate, biomaterial, cut-offs, and performing laboratory 1.
• Document quality metrics and any limitations affecting interpretation 1.
• Treat all test data as confidential medical information with appropriate security 3.

When Results Are Discordant or Uncertain

• Seek expert consultation from specialized centers when results conflict with clinical presentation 1.
• Use methodologically different assays to confirm unexpected positive results 1.
• Consider timing of testing relative to disease activity and treatment 1.
• Re-evaluate clinical data thoroughly – specialist case review after initial test stratification improves diagnostic accuracy 1.