In clinical toxicology billing, tests are grouped into drug classes (e.g., amphetamines, benzodiazepines, opiates, cannabinoids). Your LIS maps each analyte/result to one of these classes and uses the class counts and test methodology to select the correct billing codes for each date of service.

Two major billing paths

• Presumptive screening (immunoassay)
  • Typical codes: CPT 80305 (visual), 80306 (instrumented read), 80307 (instrumented with direct optical).
  • Billed once per date of service per patient, not per drug class.
  • Add modifier QW when the test is CLIA-waived and payer policy requires it.
• Definitive testing (e.g., LC-MS/MS or GC-MS)
  • Many payers (including Medicare) use tiered HCPCS G-codes based on the number of drug classes tested that day:
    • G0480: 1–7 classes
    • G0481: 8–14 classes
    • G0482: 15–21 classes
    • G0483: 22+ classes
  • Class counting is for classes tested (ordered/performed), not only positives.
  • Units are typically 1 per date of service; do not bill per analyte when the payer requires class-based G-codes.

How the LIS typically implements this

1. Map each analyte to a CMS/AMA-recognized drug class.
2. At result finalization, count unique classes tested for the DOS.
3. Apply payer-specific rules to choose presumptive vs. definitive codes and, for definitive, the correct G048x tier.
4. Link each billed line to appropriate ICD‑10‑CM diagnoses supplied by the ordering provider.
5. Enforce edits: mutually exclusive codes, frequency limits/MUEs, and same-day duplicate logic.

Common rules and nuances

• Don’t double-count metabolites within the same class (e.g., morphine/oxycodone subcomponents within opioids).
• Method matters: only tests meeting “definitive” criteria (e.g., LC/GC-MS) should be billed with definitive codes.
• Presumptive + definitive on the same DOS may be allowed when medical necessity is met; follow payer policy and NCCI edits.
• Specimen validity tests (e.g., creatinine, oxidants, specific gravity) may be bundled by many payers; bill separately only when policy allows.
• Reference/outside lab work may require modifier 90; repeat same-day tests, when allowed, may require modifier 91.
• Therapeutic drug assays (TDM) are billed with different CPT codes and are not part of tox class tiers.

Examples

• Immunoassay screen covering 12 classes on one day: bill CPT 80307 x1 (not 12 units).
• Definitive LC-MS/MS on 12 classes: bill G0481 x1 for that DOS.
• Definitive LC-MS/MS on 25 classes: bill G0483 x1 for that DOS.

Best practices

• Maintain a governed analyte-to-class mapping table with versioning.
• Validate claims against payer policies, NCCI edits, and MUEs before submission.
• Capture diagnoses at order entry; ensure each billed line links to an appropriate ICD‑10‑CM code.
• Document reflex criteria and medical necessity for moving from presumptive to definitive testing.
• Review payer updates regularly; some commercial payers mirror Medicare G-codes, others may require different coding.

Note: Coverage and coding rules vary by payer and jurisdiction and change over time. Use this as general guidance, and consult current payer policies and AMA/CMS guidance for specifics.

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