CPT, HCPCS, ICD-10, DRG and Revenue Codes Explained

Current Procedural Terminology codes are maintained by the American Medical Association and describe procedures and services.^[1] Ranges worth recognizing:

• 99202–99215 — office visits, new and established patients.
• 99281–99285 — emergency department visit levels 1–5.
• 10004–69990 — surgery.
• 70010–79999 — radiology.
• 80047–89398 — pathology and laboratory.
• 90281–99607 — medicine, vaccines, infusions.

Office and ER visit levels are driven by complexity and time. A level 4 or 5 attached to a ten-minute visit is the single most checkable error on a bill.

Two-character suffixes attached to a CPT code alter how it's paid:

• -25 — a separate, significant E/M service on the same day as a procedure. Heavily abused; it converts one visit into two charges.
• -59 — distinct procedural service, used to bypass bundling rules.
• -26 / -TC — professional vs. technical component (the radiologist vs. the machine).
• -50 — bilateral procedure.
• -76 / -77 — repeat procedure by same or different provider.
• -GA — a waiver of liability notice is on file.

If you see modifier -25 or -59 on your bill, ask the provider to explain in writing what separate service it represents.

CMS maintains HCPCS Level II for items CPT doesn't cover: injectable drugs (J-codes), durable medical equipment (E-codes), ambulance (A-codes), and supplies.^[2] Drug codes are billed by unit, and unit errors are a classic overcharge — verify the dose you received against the units billed.

Diagnosis codes justify the procedure. If the ICD-10 code doesn't support the CPT code, the claim is denied as not medically necessary — and the fix is usually a corrected code, not an appeal about the treatment.^[3] Check the diagnosis on your EOB: a wrong diagnosis code can also follow you into future underwriting and records.

For an admitted patient, Medicare and many commercial payers pay a single bundled amount based on the Medicare Severity Diagnosis Related Group, derived from the principal diagnosis, procedures, complications and comorbidities.^[4] Two consequences matter to patients: the itemized charges may total far more than the hospital is actually paid, and "DRG creep" — coding a stay into a higher-severity group — inflates cost sharing on percentage-based plans.

Also check your admission status. "Observation" is outpatient even after an overnight stay, and it is billed under different rules than inpatient admission.

Hospital bills (form UB-04) group charges by four-digit revenue code — 0250 pharmacy, 0300 laboratory, 0320 radiology, 0360 operating room, 0450 emergency room, 0636 drugs requiring detailed coding. Revenue codes tell you which department generated a charge, which is how you catch a lab charge on a date you weren't in the hospital.

1. Request the fully itemized bill — summary bills hide codes.
2. Look up each CPT/HCPCS code's descriptor and confirm it matches what happened.
3. Compare the charge to Medicare's rate for the same code and locality using the CMS Physician Fee Schedule lookup — a defensible benchmark in any negotiation.^[5]
4. Check units and dates on every drug and supply line.
5. Match the codes on the bill to the codes on your EOB; they must agree.

• Upcoding — a higher-level visit or severity than documented.
• Unbundling — billing components separately that have a single combined code.
• Duplicate lines — the same code and date billed twice without a repeat modifier.
• Unit errors — 100 units of a drug where 10 were given.
• Wrong date of service — charges after discharge.
• Mismatched diagnosis — an ICD-10 code unrelated to your care.