EVIDENCE LIBRARY
Comparing Two Toxicology Reports: A Specimen and Method Worksheet
Compare specimen, collection time, analyte, method, units, and reporting thresholds before treating two toxicology results as agreement or disagreement.
Before comparing two toxicology results, identify whether they describe the same specimen, collection time, substance, method, and reporting convention. This worksheet provides a structured way to record those details and formulate questions for the laboratory. It does not supply a universal conversion formula or decide which report is correct.
Why method and specimen belong beside the result
ARUP Consult distinguishes presumptive immunoassay testing from definitive testing and explains that test selection, specimen selection, and interpretation depend on the question being asked. It also identifies analytical design, detection limits, specimen quality, and individual drug handling as factors in detection. Those considerations support recording the testing context alongside each reported finding. See ARUP Consult: Drug Testing for the clinical laboratory background; a clinical reference does not establish the rules of a particular forensic testing program.
A side-by-side comparison worksheet
| Field | Report A and Report B | Question for follow-up |
|---|---|---|
| Specimen | Identifier, matrix, and source | Are these separate specimens or portions of one specimen? |
| Timing | Collection and analysis dates and times | Which time does each document actually describe? |
| Analyte | Exact compound, metabolite, or drug-class label | Are both methods addressing the same target? |
| Method | Method name and screening or definitive status | What identification criteria applied? |
| Result | Exact value or wording, including qualifiers | Is the entry quantitative, qualitative, or below a reporting threshold? |
| Units and limits | Units, cutoffs, and stated analytical limits | What does the laboratory mean by the reporting convention? |
| Record completeness | Amendments, attachments, and omitted fields | What must be obtained before comparison? |
Work through a reporting-threshold example
Consider a hypothetical pair of reports for the same named analyte. One lists a number; the other says negative. Instead of immediately calling the reports contradictory, enter the units and ask each laboratory for its reporting threshold and definition of negative. Also establish whether the reports concern the same specimen and whether either entry is only a preliminary screen. The worksheet identifies the missing questions; it does not answer them by assumption.
The reporting-cutoff guide is a starting point for the terminology. For source documents, see the laboratory records checklist.
Use a second example for differing labels
Suppose one document labels its result opiates while another names fentanyl. Record the labels exactly and ask for the tested analyte list rather than replacing both with opioids in a summary. ARUP notes that an opiate immunoassay does not detect every opioid and specifically distinguishes fully synthetic opioids from the compounds detected by such assays. The test name alone should not be expanded into a claim that every related drug was assessed.
Turn the comparison into a focused laboratory inquiry
Send the laboratory the two quoted entries and the specific unresolved field. For example: Please identify the analytes covered by this result, the specimen matrix, and the applicable reporting threshold. Keep the response with the report it explains. Record an unresolved item as unknown rather than filling it from an unrelated test directory or a generic detection-window table.
Finish with a bounded comparison statement
A useful summary identifies the matched fields, the differences, the missing records, and the question remaining for scientific review. Avoid declaring a winner from the numerical values alone. If the documents are different versions of one report, use the separate amended-report version worksheet.
Next technical checks when reports differ
If the disagreement remains after the basic worksheet, review the laboratory’s sample-preparation approach, stated LOD and LOQ definitions, instrument-maintenance records, and proficiency-testing evidence. These records help distinguish a true biological or specimen difference from a difference in analytical scope, sensitivity, or laboratory performance.
When the disputed analyte is cannabinoid-related, the THCCOOH LC-MS/MS interference example shows why matching transitions should be evaluated together with retention, ion-ratio, matrix, and validation evidence rather than treated as self-proving identification.
Prepared with AI assistance. Educational worksheet; not a diagnosis or a case-specific toxicology opinion. Clinical background source accessed September 19, 2026.