Confirmation is a separate, more specific analysis performed after an initial test meets or exceeds the screening cutoff. It identifies and measures a particular drug or metabolite in a different portion of the original specimen. This is why a presumptive screen should not be treated as a final positive result.
From specimen receipt to testing
The laboratory accessioner checks the package, seals, identifiers, specimen quantity, and custody form. An acceptable specimen receives an internal laboratory record while remaining linked to the original specimen ID. Controlled aliquots are then prepared for initial, confirmation, and validity testing.
Initial testing
Initial testing is designed to process specimens efficiently at a defined cutoff. Immunoassay is common, although federal rules also permit specified alternative technologies. A result below the initial cutoff is generally reported negative for that analyte. A result at or above the cutoff triggers confirmation; it is not yet a verified positive.
Confirmation methods
Confirmation commonly uses chromatography coupled with mass spectrometry, such as GC-MS or LC-MS/MS. Chromatography separates compounds; mass spectrometry helps identify them by characteristic mass and fragmentation patterns. The method is validated for the specimen, analyte, concentration range, selectivity, precision, accuracy, and possible interference.
The confirmation targets specific analytes rather than the broader class signal used in many screens. A screen for an opioid class, for example, is followed by analysis for the individual opioid or metabolite included in the panel.
Cutoffs and quantitative values
A cutoff is an administrative and analytical decision threshold—not a boundary between impaired and unimpaired. Federal programs publish required initial and confirmation cutoffs. Clinical programs may use different reporting limits based on their purpose. A value above the cutoff does not reliably reveal the exact dose, time of use, frequency, or behavioral effect.
Validity testing
For urine, the laboratory may measure creatinine, specific gravity, pH, oxidants, or other markers to classify a specimen as dilute, substituted, adulterated, or invalid under the governing criteria. Validity testing is separate from drug identification. Both results may be reported to the MRO.
Quality controls in every batch
Laboratories use calibrators, negative and positive controls, internal standards, blanks, carryover checks, and acceptance criteria. Failed controls require investigation and may invalidate or delay a batch. Instruments are maintained and calibrated, staff competency is documented, and unusual results receive technical review.
What is reported
The laboratory reports an authorized category such as negative, confirmed positive for a named analyte, adulterated, substituted, invalid, or rejected for testing. In federal workplace programs the result goes to the MRO, not directly to an ordinary supervisor. The MRO then performs the verification process and reports the appropriate final result.
Retesting and the split specimen
When the program provides a split specimen, the B bottle remains sealed unless the donor timely requests testing after an eligible verified result. A second qualified laboratory tests the split to reconfirm the presence of the analyte or validity finding. Split testing is not a new collection and does not use the ordinary initial cutoff in the same way.
Learn how the medical review works in The Role of the Medical Review Officer.
Sources
Scientific and regulatory review: October 29, 2026.