A federally regulated workplace urine specimen screens positive for amphetamines. Validity tests are normal: creatinine 85 mg/dL [7.5 mmol/L], specific gravity 1.018, pH 6.2 and no oxidants. GC-MS confirmation finds methamphetamine 920 ng/mL and amphetamine 140 ng/mL (confirmation cutoffs 250 and 100 ng/mL). Chiral analysis shows that 94% of the methamphetamine is the l-isomer. At the medical review, the donor reports using a nonprescription nasal decongestant inhaler several times a day for a week, and he has no prescriptions. The best interpretation is:

Consistent with the nonprescription inhaler

Confirmed use of illicit methamphetamine

Use of a prescribed amphetamine product

Pseudoephedrine cross-reacting in the screen

A urine cannabinoid immunoassay (cutoff 50 ng/mL) is positive. GC-MS finds THC-COOH at 9 ng/mL (confirmation cutoff 15 ng/mL). How should the result be reported?

Invalid; collect a new specimen

Positive, since THC-COOH was found

A 2-year-old has a fingerstick (capillary) blood lead of 14 µg/dL [0.68 µmol/L]. The CDC blood lead reference value is 3.5 µg/dL [0.17 µmol/L]. What is the next step?

Confirm with a venous blood lead level

Collect a 24-hour urine for lead

Measure zinc protoporphyrin instead

Repeat the capillary lead next year

A urine amphetamine immunoassay is positive in a donor who takes pseudoephedrine for a cold. What should the laboratory do next?

Confirm the result by GC-MS or LC-MS/MS

Toxicology: heavy metals, drugs of abuse and test procedures

10 ASCP MLS practice questions on Toxicology: heavy metals, drugs of abuse and test procedures, part of Chemistry. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A federally regulated workplace urine specimen screens positive for amphetamines. Validity tests are normal: creatinine 85 mg/dL [7.5 mmol/L], specific gravity 1.018, pH 6.2 and no oxidants. GC-MS confirmation finds methamphetamine 920 ng/mL and amphetamine 140 ng/mL (confirmation cutoffs 250 and 100 ng/mL). Chiral analysis shows that 94% of the methamphetamine is the l-isomer. At the medical review, the donor reports using a nonprescription nasal decongestant inhaler several times a day for a week, and he has no prescriptions. The best interpretation is:
1. AConfirmed use of illicit methamphetamine
2. BUse of a prescribed amphetamine product
3. CPseudoephedrine cross-reacting in the screen
4. DConsistent with the nonprescription inhaler
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Answer: D · Consistent with the nonprescription inhaler
Methamphetamine exists as d- and l-isomers, and routine GC-MS does not tell them apart. Illicit methamphetamine is almost all d-isomer, while some nonprescription nasal inhalers contain levmetamfetamine, the l-isomer, which is partly metabolized to l-amphetamine. Under federal medical review guidance, l-methamphetamine above 80% of the total is consistent with such an inhaler, so the result is not verified as illicit use (selegiline, which he does not take, also yields the l-isomer). Pseudoephedrine can cross-react in the screen, but it is not converted to methamphetamine and would not be confirmed by GC-MS. Amphetamine products produce amphetamine without methamphetamine.
- A: Illicit methamphetamine is mainly the d-isomer, but here 94% is the l-isomer.
- B: Amphetamine products give amphetamine without methamphetamine, and he has no prescriptions.
- C: GC-MS confirmed methamphetamine itself, which pseudoephedrine does not produce.
Question 2 · Hard
A urine cannabinoid immunoassay (cutoff 50 ng/mL) is positive. GC-MS finds THC-COOH at 9 ng/mL (confirmation cutoff 15 ng/mL). How should the result be reported?
1. AInvalid; collect a new specimen
2. BNegative for cannabinoids
3. CPositive, since THC-COOH was found
4. DPositive, based on the screen
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Answer: B · Negative for cannabinoids
The immunoassay measures THC-COOH together with other cross-reacting cannabinoid metabolites, while GC-MS measures THC-COOH alone. That is why the confirmation cutoff is lower than the screening cutoff. A confirmed result must be at or above the confirmation cutoff, so 9 ng/mL is reported as negative. In workplace testing the screen alone is presumptive and is never the final positive result.
- A: Nothing suggests tampering, so the specimen is not invalid.
- C: Drug found below the confirmation cutoff is reported as negative.
- D: A positive screen is only presumptive until it is confirmed.
Question 3 · Hard
A workplace urine specimen gives: temperature 34 °C, creatinine 1.4 mg/dL [0.12 mmol/L], specific gravity 1.0008, pH 6.5, no oxidants detected. How is this specimen classified under federal (HHS) criteria?
1. ADilute
2. BAdulterated
3. CInvalid
4. DSubstituted
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Answer: D · Substituted
Federal criteria call a specimen substituted when creatinine is below 2 mg/dL and specific gravity is 1.0010 or less (or 1.0200 or more), confirmed on two tests. Human urine almost never has values this low, so the specimen is treated as not being urine. A dilute specimen has creatinine of at least 2 but below 20 mg/dL with a specific gravity above 1.0010 but below 1.0030. Adulterated requires an adulterant or a pH far outside the physiologic range.
- A: Dilute needs creatinine of at least 2 mg/dL and a specific gravity above 1.0010.
- B: No adulterant was found and the pH is physiologic.
- C: Invalid applies when results conflict, such as creatinine below 2 mg/dL with a specific gravity between 1.0010 and 1.0200.
Question 4 · Hard
A 2-year-old has a fingerstick (capillary) blood lead of 14 µg/dL [0.68 µmol/L]. The CDC blood lead reference value is 3.5 µg/dL [0.17 µmol/L]. What is the next step?
1. ACollect a 24-hour urine for lead
2. BConfirm with a venous blood lead level
3. CMeasure zinc protoporphyrin instead
4. DRepeat the capillary lead next year
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Answer: B · Confirm with a venous blood lead level
Capillary samples are easily contaminated by lead on the skin, so a raised capillary result is only a screening result and must be confirmed with a venous sample. Higher capillary levels call for faster confirmation. Case management and environmental assessment are then based on the confirmed venous level. Zinc protoporphyrin is not sensitive at these lower lead levels.
- A: Urine lead does not reflect blood lead or body burden in children.
- C: Zinc protoporphyrin is insensitive at these lead levels and does not confirm lead.
- D: A raised level needs prompt confirmation, not a yearly recheck.
Question 5 · Medium
A urine amphetamine immunoassay is positive in a donor who takes pseudoephedrine for a cold. What should the laboratory do next?
1. AReport the result as positive
2. BConfirm the result by GC-MS or LC-MS/MS
3. CDilute the urine and re-screen
4. DRepeat the same immunoassay
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Answer: B · Confirm the result by GC-MS or LC-MS/MS
Screening immunoassays use antibodies that can cross-react with structurally similar compounds, and sympathomimetic amines such as pseudoephedrine are a classic cause of a false-positive amphetamine screen. A positive screen is therefore only presumptive. Gas or liquid chromatography with mass spectrometry identifies the specific drug from its retention time and mass fragments. Only a confirmed result is reported as positive in workplace or forensic testing.
- A: A screen alone is only presumptive and may be a false positive.
- C: Dilution does not tell a true drug from a cross-reacting one.
- D: Repeating the same assay repeats the same cross-reaction.
Question 6 · Medium
Lead poisoning raises zinc protoporphyrin in red cells mainly because lead inhibits:
1. AALA synthase
2. BFerrochelatase
3. CUroporphyrinogen decarboxylase
4. DPorphobilinogen deaminase
Answer and explanation in LearnFree account
Question 7 · Medium
An opiate immunoassay designed to detect morphine is most likely to miss which drug?
1. ACodeine
2. BHeroin
3. CMorphine-3-glucuronide
4. DFentanyl
Answer and explanation in LearnFree account
Question 8 · Medium
At a workplace urine collection, the temperature strip reads 30 °C within 4 minutes. Under federal rules, the collector should:
1. AWarm the specimen and read the strip again
2. BSend it labeled as a dilute specimen
3. CStart a new, directly observed collection
4. DAccept the specimen if the creatinine is normal
Answer and explanation in LearnFree account
Question 9 · Easy
The preferred specimen for measuring blood lead is:
1. AWhole blood in a lead-free EDTA tube
2. BRandom urine in a plastic cup
3. CPlasma from a lithium heparin gel tube
4. DSerum in a plain red-top tube
Answer and explanation in LearnFree account
Question 10 · Hard
Mass spectrometry confirmation of a urine specimen shows morphine 3,800 ng/mL and 6-acetylmorphine 45 ng/mL. Codeine is not detected. These results indicate use of:
1. APoppy seeds
2. BHeroin
3. CPrescribed morphine
4. DCodeine
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Toxicology: heavy metals, drugs of abuse and test procedures

A urine cannabinoid immunoassay (cutoff 50 ng/mL) is positive. GC-MS finds THC-COOH at 9 ng/mL (confirmation cutoff 15 ng/mL). How should the result be reported?

A workplace urine specimen gives: temperature 34 °C, creatinine 1.4 mg/dL [0.12 mmol/L], specific gravity 1.0008, pH 6.5, no oxidants detected. How is this specimen classified under federal (HHS) criteria?

A 2-year-old has a fingerstick (capillary) blood lead of 14 µg/dL [0.68 µmol/L]. The CDC blood lead reference value is 3.5 µg/dL [0.17 µmol/L]. What is the next step?

A urine amphetamine immunoassay is positive in a donor who takes pseudoephedrine for a cold. What should the laboratory do next?

Lead poisoning raises zinc protoporphyrin in red cells mainly because lead inhibits:

An opiate immunoassay designed to detect morphine is most likely to miss which drug?

At a workplace urine collection, the temperature strip reads 30 °C within 4 minutes. Under federal rules, the collector should:

The preferred specimen for measuring blood lead is:

Mass spectrometry confirmation of a urine specimen shows morphine 3,800 ng/mL and 6-acetylmorphine 45 ng/mL. Codeine is not detected. These results indicate use of: