Interpreting Laboratory Results: A Comprehensive Guide
Laboratory test interpretation requires careful consideration of multiple factors including specimen collection, analytical methods, reference ranges, and clinical context to ensure accurate diagnosis and appropriate patient management.
Key Principles for Laboratory Test Interpretation
Specimen Collection and Handling
- Direct observation is the most reliable method for urine specimen collection, especially for drug testing 1
- For specialized testing, proper specimen handling is critical (e.g., shipping at 4°C or on dry ice for certain biomarkers) 1
- Improper collection can lead to false-positive or false-negative results 1
Understanding Reference Ranges
- Reference ranges should be established by the performing laboratory and periodically verified per CLSI guidelines 1
- Age-dependent reference ranges are crucial for certain analytes (e.g., Glc4 in lysosomal disease testing) 1
- Reference ranges describe the population from which they were determined and may not apply to all individuals 2
Interpreting Results in Clinical Context
- Results should be interpreted considering:
- Patient's age
- Previous test results
- Clinical presentation
- Medication history
- Family history 1
Common Pitfalls in Laboratory Interpretation
False Positives
- Cross-reactivity with unrelated substances (e.g., fluoroquinolone antibiotics cross-reacting with opiate screens) 1
- Prescribed medications metabolizing into substances included in testing panels 1
- Specimen adulteration or contamination 1
False Negatives
- Timing of sample collection relative to exposure/disease activity 1
- Cutoff concentrations set too high 1
- Testing for limited panels that miss variant metabolites 1
- Attenuated phenotypes not showing evidence of substrate accumulation 1
Specialized Testing Considerations
Drug Testing
- Interpretation requires knowledge of:
- Complete medical history including prescribed medications
- Limitations of the selected matrix
- Substances included in the test panel
- Potential cross-reactivity 1
- Standard panels may miss newer substances (e.g., "spice" and designer drugs) 1
- Benzodiazepine panels that identify oxazepam will not detect clonazepam 1
Genetic and Metabolic Testing
- Results should be reviewed by qualified specialists (e.g., board-certified clinical biochemical geneticist) 1
- Normal results do not necessarily rule out disease, especially in patients with attenuated phenotypes 1
- Interpretation should include assessment of other laboratory findings (e.g., enzyme analysis, gene sequencing) 1
Immunological Testing
- For antiphospholipid antibody testing:
- Concurrent testing for multiple antibodies is recommended (LA, aCL IgG/IgM, aβ2GPI IgG/IgM) 1
- Results should be interpreted according to local cutoff values 1
- Two consecutive positive tests at least 12 weeks apart are needed to rule out transient positivity 1
- Triple and double antibody positivity increases confidence in diagnosis 1
Reporting Best Practices
Structure and Format
- Key information should be highlighted in a simple, easy-to-read format 1
- Actionable findings should appear on the first page of reports 1
- Reports should be integrated into electronic medical records 1
Content Requirements
- Patient and specimen information 1
- Identification of all relevant compounds 1
- Appropriate reference ranges 1
- Method description and limitations 1
- Interpretation of abnormal results including:
- Overview of results and potential significance
- Correlation with clinical information
- Differential diagnosis
- Recommendations for follow-up studies 1
Communication of Results
- In cases of new diagnosis, laboratories should attempt to reach the ordering physician directly 1
- Complex results may benefit from multidisciplinary team discussion 1
- Seeking assistance from the testing laboratory is important when results don't correlate with clinical findings 1
Conclusion
Laboratory test interpretation is a complex process that requires understanding of pre-analytical, analytical, and post-analytical factors. By following these guidelines and maintaining open communication between clinicians and laboratory specialists, accurate interpretation can be achieved, leading to improved patient outcomes.