10.4 Toxicology Within CMLA Scope

AMT III.5.D requires you to know what toxicology tests are within the laboratory assistant's scope of practice and to perform those tests. Toxicology on CMLA is not a license to run a mass spectrometer. It is waived screening you can actually complete, plus the preanalytic work for tests you must not assay yourself. Chapter 5 already taught the confirmatory rule for urine drug screening (GC/MS or LC/MS). This section applies that rule to daily toxicology without repeating the whole confirmatory chapter.

Quick Answer: Perform waived urine immunoassay drug screens (cups or cards) exactly per the IFU. A positive screen is presumptive. Confirmation, when required, is gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/mass spectrometry (LC/MS) — high complexity, not CMLA independent work. Therapeutic drug monitoring (TDM) is usually not waived: you collect the timed specimen; MLT/MLS assay it. Random clinical urine is not chain-of-custody workplace testing.

What toxicology the assistant actually performs

Toxicology here means detecting drugs, drugs of abuse, or toxins. The waived methods you will see in clinics, urgent care, and pain-management offices are immunoassay cups, dip cards, or cassettes that use antibodies to flag drug classes (for example amphetamines, cocaine metabolite, opiates, cannabinoids/THC, benzodiazepines, depending on the panel).

If the device is a cup you dip or a card you read at 5 minutes, and the IFU and CLIA certificate say waived, that is the toxicology test III.5.D is pointing at. If the device is a benchtop chromatograph in a locked room, it is not.

Scenario. A pain-management clinic uses a waived 10-panel urine cup. The CMLA identifies the patient, collects the urine per the clinical SOP, checks that volume and (if the cup requires it) temperature are acceptable, starts the timer, and reads within the window. A line pattern the IFU calls presumptive positive for benzodiazepines is reported as a screen, and the aliquot is sent for GC/MS if the SOP or IFU requires confirmation. The CMLA does not "call the patient a benzodiazepine abuser" from the cup, and does not skip confirmation because the clinic is busy.

Screening is presumptive; confirmation is GC/MS or LC/MS

Immunoassay screens are class-based and can cross-react. That is why AMT I.2.C names confirmatory testing for urine drug screening as GC/MS or LC/MS. Those methods separate and identify specific compounds. They are high complexity. A second waived cup from the same void is not confirmation. Diluting the urine with water is not confirmation; it is modified use and can push a true positive below the screen cutoff.

False-positive screens happen. Over-the-counter decongestants, some antibiotics, poppy-seed ingestion relative to some opiate cutoffs, and other cross-reactants appear in manufacturer limitation lists. A CMLA does not argue pharmacology with the patient at the cup. You report the screen as the IFU directs (presumptive positive / negative / invalid), preserve the specimen for confirmation, and let the confirmatory laboratory identify the compound.

False-negative screens happen too: the drug is below the cutoff, the urine is dilute, the collection was too early or too late relative to use, or an adulterant interfered. Invalid temperature, bleach smell, or an out-of-range specific-gravity/creatinine adulteration check (when the SOP uses them) means you do not report a clean negative from a tampered specimen.

Cutoffs are printed on the cup or in the IFU. AMT does not publish an ng/mL table. Example manufacturer immunoassay cutoffs you might see labeled on a kit include 50 ng/mL for some THC screens or 300 ng/mL for some opiate screens — those figures are examples from labeled cups, not numbers to memorize as national law. Read this kit. Changing a cutoff, reading past the time window, or using an expired cup is off-label (Chapter 5) and defaults the method to high complexity.

Follow the insert on whether a line means positive or negative; many competitive immunoassays use absence of a test line as presumptive positive. Do not invert the legend because a blood glucose strip works the other way.

Therapeutic drug monitoring is usually not a waived cup

Therapeutic drug monitoring (TDM) measures a prescribed drug in blood so the clinician can keep the dose in a therapeutic window (too low: treatment fails; too high: toxicity). Common TDM examples you will see on requisitions include vancomycin, gentamicin, digoxin, lithium, phenytoin, valproate, and similar agents. These assays are typically serum or plasma chemistry/immunoassay methods on the main analyzer — not waived urine cups and not CMLA independent assays.

Your TDM job is preanalytic:

• Collect at the named time: trough (just before the next dose) versus peak (at the SOP interval after a dose). A vancomycin trough drawn two hours late is the wrong specimen, even if the tube type is perfect.
• Use the tube the SOP names (often a red top or the named heparin; EDTA can interfere with some assays).
• Process, centrifuge, and decant per chemistry rules (Section 10.1) so the supernatant reaches the bench without cells sitting too long.
• Label peak versus trough clearly.

Do not dip a urine drug cup into a TDM order. Lithium TDM is a blood test; a urine immunoassay does not replace it.

Random clinical collections versus chain of custody

Random urine for a clinical drug screen means the specimen is collected at an unscheduled clinical visit for medical care. Follow the clinical SOP: identification, labeling, IFU timing, and confirmatory send-out when indicated. Privacy and HIPAA still apply (Chapter 16).

Chain-of-custody collections are for workplace, legal, or forensic toxicology. Chapter 8 covers specimens used as legal evidence: sealed containers, custody forms, photo ID, restricted access, and documented handoffs. A random unlabeled clinic cup cannot later be relabeled as a Department of Transportation workplace test. If the order is legal/forensic, stop and follow that procedure — including any collector training the employer or law requires — rather than "just running a waived cup" because waived cups are in CMLA scope.

Temperature strips on forensic cups, bluing in the toilet, and timed voids are chain-of-custody tools, not decorations. Clinical random collections may not use those steps; legal collections must use the ones the protocol names.

Exam traps

• Treating a waived cup as GC/MS confirmation.
• Independently performing TDM assays because "toxicology is in CMLA scope."
• Inventing a cutoff instead of reading the labeled manufacturer cutoff.
• Diluting urine to "help" a screen.
• Using a random clinical cup as a chain-of-custody workplace result.
• Reading a competitive immunoassay backwards (calling a missing line negative when the IFU says that pattern is presumptive positive).

Know the waived screen, send the confirmation, draw the TDM, and keep legal collections on the legal pathway.