A toxicology report looks like a structured lab document: a header with identifying and case information, a specimen section describing the sample, a methodology section naming the analytical techniques, a results table listing each substance tested with its outcome and (when quantitative) a concentration, and sometimes an interpretation written by a toxicologist. The exact layout varies by lab, but every report you’re likely to receive — whether from a workplace screen, a hospital, or a medical examiner — follows that same spine.
The Sections You’ll See on the Page
Open any toxicology report and the top of the page is administrative. You’ll find the laboratory’s name and address, a case or accession number, and identifiers for the person tested: name, date of birth, and often a medical record number or a law enforcement case number. Two dates sit near the identifiers — the date the sample was collected and the date the lab issued its findings. The gap between them tells you how long the analysis took.
Below the header is the specimen section. It names the sample type (blood, urine, hair, or oral fluid), how much was collected, and how it was obtained. In forensic reports this section ties directly to the chain of custody record, the documented trail of every person who handled the sample from collection through analysis. The chain of custody form itself lists the sample’s unique identifier, the collector’s name and signature, the collection date and time, and the type of analysis requested, with a signature at each transfer.1NCBI Bookshelf. Chain of Custody A gap in that chain — an unsigned transfer, a missing timestamp — can make the entire report worthless in court. Clinical reports from a hospital tend to be less rigid about this because the results are guiding treatment, not proving a legal case.
Next is methodology. This section names the analytical techniques the lab used. You’ll typically see a reference to an initial screening method (an immunoassay) and a confirmatory method, usually gas chromatography–mass spectrometry (GC-MS) or liquid chromatography–tandem mass spectrometry (LC-MS/MS). Methodology exists so another scientist, or an attorney, can evaluate whether the lab followed sound procedures.
Then comes the results section, which is the core of the document. It lists each substance the lab tested for, whether that substance was detected, and (when the test is quantitative) the concentration in the sample. Results read as “positive” or “negative” relative to a cutoff threshold, and positive results usually carry a number expressed in nanograms per milliliter (ng/mL) or milligrams per liter (mg/L).
Many reports close with an interpretation section where a board-certified toxicologist explains what the findings mean in context — for instance, whether a detected concentration falls within a therapeutic, toxic, or lethal range. Workplace drug screens usually skip this section entirely. Forensic and clinical reports often include it.
How Results Are Reported
The results table is where most people land first, and it’s the part most likely to be misread without context.
A “positive” result means the lab detected a substance above its cutoff threshold. A “negative” means either the substance wasn’t there or it was present below the reporting limit. Negative does not mean absent. If someone used a substance days before testing and the body had enough time to metabolize it below the cutoff, the report will say negative even though exposure occurred.
Quantitative results give you a concentration — say, 150 ng/mL of oxycodone in urine, or a blood alcohol level of 0.12 g/dL. Those numbers become meaningful only when a toxicologist interprets them against known therapeutic, toxic, and lethal ranges. Two people with identical blood concentrations of the same drug can show very different levels of impairment depending on tolerance, body weight, liver function, and whether they were taking other substances at the same time.
Qualitative results simply report detected or not detected, with no number attached. Most urine immunoassay screens are qualitative, which is standard in routine workplace testing — the employer doesn’t need to know how much marijuana metabolite is in your system, just whether it exceeds the cutoff.2StatPearls – NCBI Bookshelf. Toxicology Screening – StatPearls
What substances appear in the table depends entirely on what the lab was asked to look for. No single test screens for everything. Federal workplace drug testing follows the Mandatory Guidelines published by the Substance Abuse and Mental Health Services Administration (SAMHSA), with a standard panel covering marijuana, cocaine, opioids (codeine, morphine, hydrocodone, oxycodone, and fentanyl), amphetamines and methamphetamine, MDMA, phencyclidine (PCP), and heroin metabolites.3Federal Register. Mandatory Guidelines for Federal Workplace Drug Testing Programs Authorized Testing Panels Hospital panels tend to be broader, often including prescription medications (antidepressants, sedatives, anticonvulsants), over-the-counter drugs (acetaminophen, aspirin, antihistamines), and substances of abuse, with quantitative blood serum results to help guide treatment.2StatPearls – NCBI Bookshelf. Toxicology Screening – StatPearls Forensic panels in death investigations are typically the most comprehensive, pulling in drugs of abuse, prescription medications, alcohol, poisons, heavy metals, and sometimes volatile substances like carbon monoxide, with the medical examiner or coroner deciding what to test for based on the circumstances.
Why Screening and Confirmation Appear Separately
If you look closely at a report, you’ll often see two sets of results for the same substance: a screening result and a confirmatory result. That isn’t duplication. It reflects how the lab actually processes the sample.
The first-pass test is an immunoassay, a fast and relatively inexpensive method that checks whether a substance or class of substances is present above a preset cutoff. Immunoassays catch positives quickly but aren’t very specific. They detect antibody reactions to drug metabolites, and structurally similar compounds can trigger the same reaction. That cross-reactivity is why certain over-the-counter cold medications can produce a positive for amphetamines on an initial screen, or why poppy seeds can trigger a positive for opiates. A screening result alone doesn’t confirm the presence of a specific drug, and most urine immunoassays provide only a positive-or-negative output without exact concentrations.2StatPearls – NCBI Bookshelf. Toxicology Screening – StatPearls
Any positive screening result in a forensic or workplace context gets sent for confirmatory testing. The gold standard is mass spectrometry — GC-MS or LC-MS/MS. These instruments physically separate compounds in a sample and identify them by molecular structure, which eliminates the cross-reactivity problem. A positive from mass spectrometry is considered highly reliable because it identifies the exact compound rather than just a class.
Confirmatory testing uses its own cutoff thresholds, typically lower than the screening cutoffs. A substance can register below the screening cutoff and be reported negative on the initial test while still being present in a detectable amount. On the page, that’s why “negative” in a report doesn’t necessarily mean zero — it means the concentration fell below the lab’s reporting threshold.2StatPearls – NCBI Bookshelf. Toxicology Screening – StatPearls
What the Report Doesn’t Tell You
Even a well-run toxicology report has limits built into the format. Reading it carefully means knowing what the numbers can’t say.
A positive tells you a substance was present. It does not tell you when the person took it, how they took it, or whether they were impaired at any specific moment. A driver who tests positive for THC metabolites in urine may have last used marijuana a week before the traffic stop. Blood narrows the window but still can’t pinpoint an exact time of ingestion.
Concentration numbers are snapshots, not narratives. A blood alcohol level of 0.15 g/dL tells you the concentration at the moment the blood was drawn. Whether the person was still absorbing alcohol or already metabolizing it changes the clinical picture entirely, and the report itself can’t distinguish between those states.
Individual variation makes universal interpretation risky. A chronic opioid user prescribed high-dose pain medication may function normally at a blood concentration that would render an opioid-naive person unconscious. Tolerance, genetics, organ function, drug interactions, and recent food intake all affect how a given concentration translates into actual impairment or toxicity.
No test screens for everything. A standard panel may miss newer synthetic substances, designer drugs, or uncommon poisons because the lab wasn’t looking for them. If the clinical picture doesn’t match the results, the ordering physician or medical examiner may need to request additional targeted testing.
Extra Elements on a Post-Mortem Report
Toxicology reports from death investigations usually carry sections and caveats you won’t see on a workplace or clinical report, because post-mortem samples behave differently from samples drawn from a living person.
After death, drugs redistribute within the body. This phenomenon, called postmortem redistribution, causes drug concentrations measured from blood drawn near the heart or major organs to read significantly higher than blood drawn from a peripheral vein in the arm or leg. Basic, fat-soluble drugs with large volumes of distribution are especially prone to this effect, as they leach from organ tissue back into surrounding blood after death.4PMC. Postmortem Redistribution of Drugs: A Literature Review A forensic toxicologist accounts for this by comparing central and peripheral blood concentrations and noting the collection site on the report. If you’re looking at a post-mortem report, check the specimen section carefully — it should identify where in the body each sample came from.
Decomposition adds another layer. Bacterial activity can produce ethanol in a body after death, potentially creating a false positive for alcohol consumption. The longer the interval between death and sample collection, the less reliable concentration measurements become. For these reasons, post-mortem toxicology reports almost always include an interpretation section where the toxicologist explains how these factors affect the findings. A high concentration alone doesn’t prove the drug caused death without that interpretation.
Signs of a Credible Report
Beyond the data itself, a few markers on the page tell you whether the report is one a court or physician will trust.
Look for the lab’s accreditation. Clinical labs that perform toxicology testing on patient samples must be certified under the Clinical Laboratory Improvement Amendments (CLIA). CLIA categorizes toxicology as a subspecialty of chemistry and requires labs to pass proficiency testing — scoring at least 80 percent on acceptable responses for each substance tested — to maintain certification.5eCFR. 42 CFR Part 493 – Laboratory Requirements Labs that fall below that threshold in two consecutive testing events face sanctions. Forensic labs performing federal workplace drug testing face a separate certification process through the National Laboratory Certification Program (NLCP), overseen by the Department of Health and Human Services. NLCP certification requires testing three rounds of performance samples, passing an on-site inspection, and undergoing re-inspection every six months.6Office of Justice Programs. Mandatory Guidelines for Federal Workplace Drug Testing Programs Supporting Statement Certified labs must maintain documented chain of custody procedures, quality control records, and personnel training records.
Check whether the issuing lab lists its CLIA certificate number or NLCP certification somewhere on the report. Check the chain of custody record for complete signatures and timestamps at every transfer. Check that the methodology section names a confirmatory method, not just a screening method, for any positive result being used in a legal setting. A report from an uncertified lab, or one with gaps in its chain of custody, will face much harder scrutiny in any proceeding where it matters.