Bottom Line Up Front
LC-MS/MS cutoffs: Morphine & Codeine = 50 ng/mL (urine), 1 ng/mL (oral fluid). Any result below these thresholds is clinically and legally Negative. Results are truncated (not rounded): 19.9 becomes 19. The 1% Rule requires the parent compound to be at or above 50 ng/mL before it can be applied to explain secondary opioids.
Specimen Validity & Adulteration
| Creatinine (mg/dL) | Interpretation |
|---|---|
| < 2.0 | Physiologically Impossible: not human urine |
| 2.0 – 5.0 | Highly Improbable: suggests direct water addition |
| 5.0 – 20.0 | Dilute: excessive fluid intake or water addition |
| 2.0 – 20.0 with SG > 1.020 | Probable Non-Urine: possible substitution (e.g., juice) |
| > 20.0 | Normal range |
Normal range: 1.002 – 1.020.
Decreased SG may also indicate renal failure, glomerulonephritis, pyelonephritis, or diabetes insipidus.
| SG Value | Interpretation |
|---|---|
| < 1.003 | Dilute / Tampered |
| 1.003 – 1.020 | Normal |
| > 1.020 (with Cr 2–20) | Suspicious: possible non-urine substitution |
| pH Range | Interpretation |
|---|---|
| 4.5 – 8.0 | Normal physiological range |
| Up to 9.5 | Clinical acceptance limit |
| < 4.5 or > 8.0 (SAMHSA forensic limit: 9.1) | Tampered |
Clinical labs accept pH up to 9.5 to account for bacterial urea hydrolysis during transport; bacteria degrade urea into ammonia, raising pH. Pain medications remain stable in urine up to pH 9.5. SAMHSA forensic cutoff is 9.1; clinical standard is 9.5.
- Bleach (sodium hypochlorite): oxidizing agent; degrades drug metabolites; detected via oxidant screen and abnormal odor
- Vinegar / ammonia: shifts pH to extremes; detected by pH testing
- Detergents / soaps: increase viscosity; cause foamy or scented urine
- Commercial products (Urine Luck, CleanX): interfere with immunoassays
- Powdered or synthetic urine: abnormal SG/creatinine pairing, often gelatinous texture
High viscosity alone (sticky, gelatinous, or foamy urine) is a red flag for adulteration. Reject and request a new specimen.
Yes. A dilute specimen can still contain drug metabolites at detectable levels. Quantitative results in dilute specimens should be interpreted cautiously; creatinine-normalized values help contextualize the finding.
Opiates & MAT (Buprenorphine, Methadone, Opioids)
| Analyte | EIA Cutoff | LC-MS/MS Urine | LC-MS/MS Oral Fluid | Detection Window |
|---|---|---|---|---|
| Codeine | 300 ng/mL | 50 ng/mL | 1 ng/mL | 1–2 days |
| Morphine | 300 ng/mL | 50 ng/mL | 1 ng/mL | 1–2 days (IR); 2–3 (ER) |
Opioid Process Impurities — prescription opioids contain unavoidable manufacturing byproducts that are themselves opioids. At high doses, these impurities can be detected at low levels, raising concern about additional drug use. They are not metabolites. This concept is informally called the "1% Rule" — named because impurities are generally present at less than 1% of the parent drug concentration. The rule has one hard requirement: it cannot be applied if the parent compound is not confirmed at or above the laboratory's cutoff (typically 50 ng/mL). Without a confirmed parent, the secondary opioid must be evaluated as independent ingestion.
| Prescribed Drug | Potential Impurity | Allowable % | Typically Observed % |
|---|---|---|---|
| Codeine | Morphine | 0.15% | 0.01–0.1% |
| Morphine | Codeine | 0.5% | 0.01–0.05% |
| Hydrocodone | Codeine | 0.15% | 0–0.1% |
| Hydromorphone | Morphine, Hydrocodone | 0.15%, 0.1% | 0–0.025% |
| Oxycodone | Hydrocodone | 1.0% | 0.02–0.12% |
| Oxymorphone | Oxycodone, Hydromorphone | 0.5%, 0.15% | 0.05–0.4%, 0.03–0.1% |
* Cutoff values reflect this laboratory's thresholds. Other laboratories may use different cutoffs.
Critical Distinction: Impurity vs. Metabolite
Hydrocodone (after codeine) and hydromorphone (after morphine) are actually minor metabolites at approximately 5% of the parent drug concentration — not process impurities. This is commonly misattributed to impurities. If hydromorphone or hydrocodone appear at roughly 5% of their parent, that is metabolic, not impurity-driven.
Interpretation Criteria — a process impurity is more likely when all three conditions are present:
- The secondary opioid is not a prescribed medication
- Its urine concentration is low (generally below 100 ng/mL)
- The prescribed parent opioid is present at a high concentration (generally above 50,000 ng/mL)
Limitations
- No quantity thresholds or ratios can absolutely determine the source of an opioid
- Impurity percent varies between lots and formulations — impurities are not always detected even at elevated parent concentrations
- Interpretation must include clinical observation and professional judgment
Process impurities should be a diagnosis of exclusion, not a default explanation. All three criteria must be present and the full clinical picture considered. Hydrocodone/hydromorphone after codeine/morphine are more likely metabolites than impurities — check the ratio against the parent before attributing to manufacturing.
Codeine is metabolized to morphine via CYP2D6 (approximately 5–10% O-demethylation). A morphine result in a codeine-prescribed patient is expected and does not indicate separate morphine ingestion, provided the morphine concentration is proportionate and codeine is confirmed at or above 50 ng/mL.
Possibly not. Hydrocodone is present as a manufacturing process impurity in oxycodone at up to 1% of the oxycodone concentration. If oxycodone is confirmed at or above 50 ng/mL and hydrocodone is proportionally low (less than 1% of the oxycodone value), this is consistent with the 1% Rule and does not necessarily indicate independent hydrocodone ingestion.
Heroin is rapidly deacetylated to 6-acetylmorphine (6-AM) within minutes of administration, then further to morphine. Heroin itself is rarely detected in urine.
6-AM is the unique marker for heroin use, most likely detectable within the first 24 hours. After that window, only morphine remains, which is non-specific.
6-AM is the unique marker for heroin use, most likely detectable within the first 24 hours. After that window, only morphine remains, which is non-specific.
If 6-AM is detected, this is definitive evidence of heroin use. Morphine alone (without 6-AM) cannot distinguish between morphine prescription, codeine metabolism, and heroin use after the 6-AM window has closed.
When buprenorphine is very high (greater than 5,000 ng/mL) with no or minimal norbuprenorphine, this strongly suggests specimen spiking: direct addition of buprenorphine to the sample rather than systemic ingestion and metabolism. Genuine physiologic use produces norbuprenorphine as the primary urinary metabolite.
The buprenorphine-to-norbuprenorphine ratio is a key diversion indicator. Absence of norbuprenorphine with a high parent drug is a red flag for specimen adulteration.
Immunoassays underrespond to the glucuronide-conjugated form of norbuprenorphine that predominates in urine, while LC-MS/MS measures total (free plus conjugated after hydrolysis) more accurately. Immunoassay values may be significantly lower. The LC-MS/MS result is the authoritative value.
In urine: Methadone without EDDP is suspicious and may indicate specimen adulteration or direct powder addition. However, very low EDDP can occur physiologically.
In oral fluid: This is within expected range. In a study of 84,148 oral fluid specimens, 62.2% of methadone-positive results had no detectable EDDP. This is biologically normal in oral fluid and should not be interpreted as deception.
In oral fluid: This is within expected range. In a study of 84,148 oral fluid specimens, 62.2% of methadone-positive results had no detectable EDDP. This is biologically normal in oral fluid and should not be interpreted as deception.
Methadone without EDDP in oral fluid is common and expected. Do not use this finding alone to question a patient's adherence in oral fluid testing.
Not necessarily. A negative oral fluid result in a patient receiving long-acting injectable buprenorphine does not indicate non-adherence. Detection in oral fluid depends on passive diffusion of free drug from plasma into saliva: severely limited by buprenorphine's ~96% protein binding and the absence of direct oral cavity exposure.
| Product | Route | Approx OF Positivity |
|---|---|---|
| Suboxone (sublingual) | Direct oral exposure | ~86% |
| Sublocade | SubQ depot injection | ~47% |
| Brixadi | SubQ depot injection | Comparable to or lower than Sublocade |
For in-office-administered injectables, adherence is confirmed by the administration record: not drug testing. If confirmation is clinically needed, urine is the preferred matrix. Never use a negative oral fluid result alone to question adherence in a depot buprenorphine patient.
| Medication | Formulations | Brand Names | Testing Notes |
|---|---|---|---|
| Buprenorphine | SL tablets, SL films, ER injection, implant | Subutex, Suboxone, Sublocade, Brixadi, Belbuca, Zubsolv | Buprenorphine + norbuprenorphine detected; may cause weak opiate EIA cross-reactivity |
| Methadone | Oral solution, tablets, dispersible tablets | Methadose | Requires specific methadone assay; long half-life |
| Naltrexone | Oral tablets, ER monthly injection | Vivitrol, Revia | Not routinely detected on standard UDT panels |
| Naloxone | Nasal spray, IV/IM | Narcan, Kloxxado | May appear on some panels; structurally similar to morphine on EIA |
Crushing an ER tablet causes dose dumping: the full dose absorbs rapidly as if immediate-release (IR). For example, crushing ER alprazolam (half-life ~16 hrs) converts it to behave like IR alprazolam (half-life ~11 hrs). The urine profile shows a more rapid rise and fall in metabolite concentrations compared to the expected ER pattern.
Stimulants (Methamphetamine, Amphetamine, Cocaine)
LC-MS/MS is specific for methamphetamine and does not produce false positives from methylphenidate (Ritalin) or amphetamine salts (Adderall). Adderall contains amphetamine, not methamphetamine: these are distinct analytes.
Chiral Analysis (D/L isomer testing) differentiates sources:
Chiral Analysis (D/L isomer testing) differentiates sources:
| % d-isomer | Interpretation | Source |
|---|---|---|
| 20% or more d-MAMP | Positive for d-isomer | Illicit methamphetamine or Rx (Desoxyn, Didrex) |
| Less than 20% d-MAMP | Positive for l-isomer | OTC Vicks Inhaler or selegiline metabolism |
| Any result above 10,000 ng/mL | Strongly illicit | Effectively excludes OTC/selegiline |
When methamphetamine AND amphetamine are both detected, some methamphetamine is metabolized to amphetamine: this is expected and does not indicate separate amphetamine ingestion.
Yes. Topical cocaine (used in ENT/dental procedures) is systemically absorbed and produces a positive urine benzoylecgonine result. The patient's clinical history should be considered. Coca leaf teas can also produce positive results.
Yes. In approximately 31% of oral fluid cases, benzoylecgonine is absent despite a positive cocaine result, due to pharmacogenomic variance in esterase activity in saliva.
Absence of benzoylecgonine in oral fluid does NOT invalidate a positive cocaine result. The parent drug is the primary analyte in oral fluid testing. This is biologically normal, not a lab error.
Current evidence suggests semen-mediated cocaine transfer is highly unlikely to produce a positive urine result at standard clinical cutoffs (50–100 ng/mL BE). Based on the available data, this pathway is not expected to generate detectable benzoylecgonine in a partner's urine under typical conditions. However, the published literature is limited and should be applied with clinical judgment.
The only primary data comes from Cone et al. (1996), a letter-level report measuring cocaine in seminal plasma of drug users. Peak seminal plasma cocaine was approximately 10 mcg/g in chronic heavy users. A typical ejaculate is 2–3 grams, yielding an estimated maximum of 20–30 mcg cocaine per encounter. The authors extrapolated approximately 10,000 precisely timed sexual encounters before a non-using partner might approach a positive drug test. No published study has documented a confirmed positive attributable to this pathway.
A separate scenario is direct urine specimen contamination — if semen is deposited shortly before voiding and collection is not done cleanly. If suspected, prostate-specific antigen (PSA) testing can serve as a seminal marker.
The only primary data comes from Cone et al. (1996), a letter-level report measuring cocaine in seminal plasma of drug users. Peak seminal plasma cocaine was approximately 10 mcg/g in chronic heavy users. A typical ejaculate is 2–3 grams, yielding an estimated maximum of 20–30 mcg cocaine per encounter. The authors extrapolated approximately 10,000 precisely timed sexual encounters before a non-using partner might approach a positive drug test. No published study has documented a confirmed positive attributable to this pathway.
A separate scenario is direct urine specimen contamination — if semen is deposited shortly before voiding and collection is not done cleanly. If suspected, prostate-specific antigen (PSA) testing can serve as a seminal marker.
| Parameter | Value / Notes |
|---|---|
| Peak cocaine in seminal plasma | ~10 mcg/g (Cone 1996, letter-level; limited sample) |
| Estimated cocaine per ejaculate | ~20–30 mcg maximum |
| BE needed for 50 ng/mL positive (300 mL void) | ~15 mcg minimum, before distribution and clearance |
| Encounters to approach a positive (est.) | ~10,000 (author extrapolation, not empirically validated) |
| Published confirmed positives via semen | None identified in peer-reviewed literature to date |
* Cutoff values reflect this laboratory's thresholds. Other laboratories may use different cutoffs — confirm with the reporting lab before making clinical decisions.
When evaluating this claim, consider the reported BE concentration. Higher concentrations make the explanation progressively less plausible. The mass-balance calculation alone does not support this mechanism at standard cutoffs under typical conditions — but present this as current evidence, not settled science.
"Thank you for calling. I understand you have a question about a positive cocaine result in a patient claiming exposure through her partner."
[Listen for the reported concentration and collection circumstances before responding.]
"Based on the available evidence, semen-mediated cocaine transfer is not expected to produce a positive urine result at standard cutoffs. The cocaine concentrations documented in semen are too low, and the volume per encounter too small, to generate detectable benzoylecgonine in a partner's urine under typical conditions."
"That said, the published literature in this area is limited, so I would not present this as completely settled. No published study has documented a confirmed positive from this pathway."
[If caller asks about concentration:] "What was the reported BE level? Higher concentrations make this explanation progressively less plausible."
[If contamination is raised:] "If there is concern about direct specimen contamination rather than systemic absorption, the specimen can be tested for PSA as a seminal marker."
"Is there anything specific about the clinical picture I can help you think through?"
THC / Cannabis
| Use Pattern | Approximate Detection Window |
|---|---|
| Single use | 3–4 days |
| Moderate use (few times/week) | 5–7 days |
| Daily use | 10–15 days |
| Chronic heavy use | Up to 30+ days |
A decreasing THC-COOH concentration over serial specimens is consistent with abstinence. An increasing level suggests new use.
Very unlikely. Even under extreme conditions (unventilated room, prolonged heavy exposure), passive inhalation produces THC-COOH levels rarely exceeding 30 ng/mL: well below the standard 50 ng/mL cutoff.
Passive inhalation is not a defensible explanation for a confirmed positive THC result at or above the 50 ng/mL cutoff under real-world conditions.
Marinol (dronabinol, synthetic THC): Yes: dronabinol is metabolized to THC-COOH and produces a positive result identical to cannabis use.
Hemp-derived CBD products: Regulated products must contain less than 0.3% delta-9-THC, but concentrated or impure products may produce a positive test, especially with heavy use.
Hemp-derived CBD products: Regulated products must contain less than 0.3% delta-9-THC, but concentrated or impure products may produce a positive test, especially with heavy use.
Delta-8, Delta-9, and Delta-10 THC are structural isomers: same molecular formula, but the double bond sits at a different position in the THC ring, changing CB1 affinity, potency, and psychoactive profile.
THC-COOH half-life is 20–60 hours for all isomers. Chronic use of any isomer produces extended detection (days to weeks).
| Isomer | Potency vs Delta-9 | Parent Half-Life | Clinical Profile |
|---|---|---|---|
| Delta-9-THC | 100% (reference) | 4–6 hrs | Classic intoxication; euphoria, impaired coordination; highest impairment risk |
| Delta-8-THC | ~50–70% | 4–8 hrs | Milder, calmer; less anxiety/paranoia; still impairing; widely sold in gas stations/vape shops |
| Delta-10-THC | ~20–40% | 4–8 hrs | More energizing/uplifting; lighter euphoria; "functional high" |
All delta isomers metabolize to the same urinary metabolite: THC-COOH. Routine LC-MS/MS confirmation cannot differentiate which isomer was used. A confirmed positive is a positive, regardless of the source isomer.
No. Standard drug testing cannot assign a THC-COOH positive to a specific isomer source.
- Many retail Delta-8/Delta-10 products contain measurable Delta-9-THC due to poor manufacturing controls
- Chronic Delta-8 or Delta-10 use produces prolonged THC-COOH positivity identical to cannabis use
- Drug courts and monitoring programs typically treat all delta isomers identically
Suggested monitoring program language: "Use of intoxicating cannabinoids (including Delta-8-THC, Delta-10-THC, HHC, and related products) is prohibited. Routine testing cannot differentiate product source. A confirmed cannabinoid positive stands regardless of claimed retail cannabinoid use."
HHC is a hydrogenated cannabinoid. Unlike delta isomers (positional), HHC's "isomers" are stereoisomers: 9R-HHC (more CB1-active, more psychoactive) and 9S-HHC (less active). Commercial HHC products are a variable mixture of both.
| Feature | Delta-9-THC | HHC (retail products) |
|---|---|---|
| Standard urine target | THC-COOH: detected on all panels | HHC-COOH-type metabolites: not included on most standard panels |
| LC-MS/MS confirmation | Confirmed as THC-COOH | Often missed or non-specifically reported; requires targeted HHC method |
A claim of "HHC only" does not explain a positive THC-COOH result. Standard confirmations detect THC-COOH, not HHC metabolites. Without a lab that specifically tests for HHC, the distinction cannot be made.
11-hydroxy-THC (11-OH-THC) is an active intermediate metabolite of THC, at least equipotent to: and often more potent than: Delta-9-THC on a mg-for-mg basis.
Oral THC (edibles, capsules) produces proportionally more 11-OH-THC than inhaled cannabis due to first-pass hepatic metabolism. This explains why oral cannabis causes stronger, longer intoxication at equivalent doses and is a common cause of unexpected overdose with edibles.
11-OH-THC is not a routine urine confirmation target: standard panels report THC-COOH only.
Oral THC (edibles, capsules) produces proportionally more 11-OH-THC than inhaled cannabis due to first-pass hepatic metabolism. This explains why oral cannabis causes stronger, longer intoxication at equivalent doses and is a common cause of unexpected overdose with edibles.
11-OH-THC is not a routine urine confirmation target: standard panels report THC-COOH only.
When a patient reports using edibles and the clinical picture seems disproportionate to the stated dose, 11-OH-THC accumulation is the pharmacological explanation: not patient exaggeration.
Benzodiazepines
Chlordiazepoxide has a complex metabolic cascade: Chlordiazepoxide → Desmethylchlordiazepoxide → Demoxepam → Nordiazepam → Oxazepam. All metabolites may appear in urine.
A patient prescribed only chlordiazepoxide (Librium) can test positive for nordiazepam and oxazepam. These are expected metabolites, not evidence of additional benzodiazepine use.
The LC-MS/MS result is correct. Buprenorphine can cross-react with some immunoassay opiate panels at high concentrations due to structural similarity to other opioids. The immunoassay is a screening test only: LC-MS/MS is the authoritative result.
Emerging Substances & Novel Psychoactives (NPS)
Crystallized pyrethroid-based insecticide (wasp spray) used as an injectable drug of abuse. Created by spraying insecticide through an electrified wire screen; the crystals resemble crystal methamphetamine.
Mechanism: Pyrethroids are sodium/chloride channel modulators that suppress GABA activity, producing a methamphetamine-like "rush."
Clinical risks: IV injection can cause multiorgan failure (lungs, heart, liver, kidneys). No specific antidote; treatment is supportive.
Geographic prevalence: Reported in KY, FL, NY, OH, TN, TX, WV.
Mechanism: Pyrethroids are sodium/chloride channel modulators that suppress GABA activity, producing a methamphetamine-like "rush."
Clinical risks: IV injection can cause multiorgan failure (lungs, heart, liver, kidneys). No specific antidote; treatment is supportive.
Geographic prevalence: Reported in KY, FL, NY, OH, TN, TX, WV.
Wasp dope is NOT detected on standard drug panels. If a patient presents with methamphetamine-like symptoms but negative toxicology, wasp dope is a differential consideration in endemic areas.
Kratom (Mitragyna speciosa) acts as a stimulant at low doses and a mu-opioid agonist at higher doses (via mitragynine). Standard drug panels do not detect kratom. Kratom can cause a false positive on some immunoassay opiate screens, but confirmatory LC-MS/MS will be negative for standard opioids.
Phenibut is a GABA-B agonist (similar to baclofen) available online as a supplement. Not detected on standard drug panels. Clinical presentation can mimic benzodiazepine or alcohol intoxication/withdrawal.
Phenibut withdrawal can be severe: similar to benzodiazepine withdrawal. Taper protocols similar to GABA-acting agents may be needed.
No. Standard labs cannot detect inhalants by urine drug testing. Inhalants are volatile compounds and must be captured via breath testing.
Nitrous oxide specifically: Half-life is approximately 5 minutes via exhalation. The standard diagnostic approach for chronic abuse is measuring B12 and homocysteine levels: nitrous oxide inactivates vitamin B12 and elevates homocysteine.
Nitrous oxide specifically: Half-life is approximately 5 minutes via exhalation. The standard diagnostic approach for chronic abuse is measuring B12 and homocysteine levels: nitrous oxide inactivates vitamin B12 and elevates homocysteine.
Yes. Topical ketamine (e.g., 10% cream) is systemically absorbed and will produce a positive result for both ketamine and its metabolite norketamine by LC-MS/MS (cutoff typically 50 ng/mL, creatinine-normalized).
Per ACMT and AACT joint statement (July 2017): incidental skin contact with fentanyl powder is extremely unlikely to cause toxicity or a positive drug test. Reported symptoms in emergency responders following skin contact have not been consistent with opioid poisoning.
A positive fentanyl result in a first responder claiming only incidental skin contact is not credibly explained by that exposure. Active inhalation or ingestion is the more plausible explanation for a confirmed positive.
Oral Fluid Testing
Standard oral fluid panels include: amphetamine, methamphetamine (MDMA and metabolite), opiates (codeine, morphine, hydrocodone, hydromorphone, 6-AM), cocaine (metabolite), THC, and PCP.
Oral fluid is a better indicator of recent use (hours to 1–2 days) compared to urine. THC in oral fluid is particularly useful as a same-day use indicator.
| Drug | Approximate OF Detection Window |
|---|---|
| Amphetamine / Methamphetamine | 1–3 days |
| Cocaine | 1–2 days |
| THC (cannabis) | 12–24 hours (current use indicator) |
| Opioids (morphine, codeine) | 1–2 days; cutoff 1 ng/mL |
| Buprenorphine | 2–3 days |
| Methadone | 1–2 days |
Long-acting injectable buprenorphine releases drug slowly into systemic circulation from a subcutaneous depot: with no direct oral cavity exposure. Detection in oral fluid depends on passive diffusion of free drug from plasma into saliva, severely limited by buprenorphine's ~96% protein binding.
| Product | Route | OF Positivity Rate |
|---|---|---|
| Suboxone (sublingual) | Direct oral exposure | ~86% |
| Sublocade | SubQ depot injection | ~47% |
| Brixadi | SubQ depot injection | Comparable to or lower than Sublocade |
For in-office-administered injectables, adherence is confirmed by the administration record. If confirmation is needed, urine is the preferred matrix. Never use a negative oral fluid result alone to question adherence in a depot buprenorphine patient.
Hand sanitizer (alcohol-based) does not significantly affect oral fluid drug results when used normally before collection. The amount of alcohol transferred to the oral cavity is insufficient to produce a positive EtG result in oral fluid.
Breath mints: Generally not a concern for drug panels. They may transiently affect pH but do not produce false positives for drugs.
Breath mints: Generally not a concern for drug panels. They may transiently affect pH but do not produce false positives for drugs.
Reporting, Cutoffs & Lab Standards
Results are truncated (decimal dropped), not rounded: carried over from forensic toxicology standards. Truncation ensures a patient is never rounded up to a positive at the cutoff level.
Example: cutoff is 20 ng/mL, raw result is 19.9 ng/mL. Rounding reports 20 (positive). Truncation correctly reports 19 (negative).
Example: cutoff is 20 ng/mL, raw result is 19.9 ng/mL. Rounding reports 20 (positive). Truncation correctly reports 19 (negative).
If a report shows 19 ng/mL for a cutoff of 20 ng/mL, the result is negative. Never assume a sub-threshold truncated result equals a positive.
| Term | Definition | Clinical implication |
|---|---|---|
| Sensitivity | Ability to correctly identify true positives (drug present, test positive) | High sensitivity = fewer false negatives |
| Specificity | Ability to correctly identify true negatives (drug absent, test negative) | High specificity = fewer false positives |
LC-MS/MS: high sensitivity AND specificity: the definitive confirmatory standard.
No. Results below the established LC-MS/MS cutoff are analytically Negative: they should be classified as "trace" or "sub-threshold" and are indefensible as the basis for clinical or legal action.
Example: A 15 ng/mL codeine result against a 50 ng/mL cutoff is 3.3 times below the reporting threshold. This result is clinically and legally Negative.
Example: A 15 ng/mL codeine result against a 50 ng/mL cutoff is 3.3 times below the reporting threshold. This result is clinically and legally Negative.
Sub-threshold "trace" data near the Limit of Detection (LOD) is considered analytically unreliable. Do not use these results to counsel or take action against patients.
| Parameter | Forensic (SAMHSA/DOT) | Clinical |
|---|---|---|
| Purpose | Employment, legal, government | Patient care, monitoring |
| pH acceptance | Up to 9.1 | Up to 9.5 |
| Chain of custody | Required | Not always required |
| Reporting | MRO review required | Direct physician interpretation |
Alcohol Biomarkers (EtG / EtS)
Not always at low concentrations. EtG detects alcohol consumption up to 72–80 hours after last use, but incidental exposure can cause low-level positives:
- Alcohol-based hand sanitizers, mouthwashes
- Some foods (kombucha, very ripe fruit, certain breads)
- Certain medications
EtG is more sensitive than EtS but also more prone to incidental exposure artifacts at low concentrations. Consider both values together and apply context: workplace vs. clinical monitoring settings may use different threshold interpretations.
Other Clinical Topics
Patients taking venlafaxine (Effexor) will test positive for both venlafaxine and its active metabolite O-desmethylvenlafaxine (desvenlafaxine). Patients taking only desvenlafaxine (Pristiq) may or may not show venlafaxine depending on minor back-metabolism. The FDA recognizes desvenlafaxine as a distinct chemical entity from venlafaxine.
Creatinine is an endogenously produced byproduct of muscle metabolism, cleared by the kidneys at a relatively constant rate. Normal urine creatinine: at or above 20 mg/dL. Used to assess urine concentration, normalize drug results, and identify specimen validity issues. Abnormal creatinine may also result from renal disease, reduced renal blood flow, or high meat diet: not always indicative of tampering.
Most drugs are detectable in urine within 2–6 hours of oral ingestion. Onset is faster with IV or inhalation routes. If a patient claims to have taken their medication right before specimen collection, detection in urine would typically require at least 2 hours for the medication to be metabolized and excreted.
No. The DEA has issued a memorandum prohibiting clinical laboratories from accepting non-patient samples for drug concentration testing. Clinical labs are authorized to test patient specimens only.
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