Medical Billing Codes Explained

CPT (Current Procedural Terminology)

Five-character codes maintained by the AMA that identify medical procedures and services.

CPT is widely used to describe professional and outpatient procedures, visits, tests, and imaging. Payment and coverage also depend on documentation, payer rules, setting, modifiers, contracts, and the plan.

Example: CPT 99213: an established-patient office or other outpatient visit. Time is one permitted selection method in applicable circumstances; medical decision-making can also determine the level.

Lookup: AMA CPT overview

Watch for: Ask what documentation and payer rule support an unfamiliar code or combination. A bill alone cannot establish upcoding, unbundling, or whether the code was supported.

HCPCS Level II

Codes for medical equipment, supplies, drugs, ambulance services, and other items not covered by CPT.

HCPCS Level II covers things like wheelchairs, crutches, injectable medications administered in a clinical setting, durable medical equipment, and ambulance transport. CPT (HCPCS Level I) covers the procedures themselves; Level II covers the items.

Example: HCPCS J3490: unclassified drug, used to bill medications that do not have a specific code.

Lookup: CMS HCPCS Level II

Watch for: If equipment is unfamiliar, ask whether it was rented or purchased and which benefit rule applied. For an unclassified drug code, ask for the drug name, quantity, and supporting detail.

ICD-10-CM

Diagnosis codes that describe the patient's condition or the reason for the visit.

ICD-10-CM describes diagnoses, symptoms, and reasons for encounters. Payers may use diagnosis information with procedure codes, documentation, coverage rules, and plan terms when processing a claim.

Example: ICD-10-CM E11.9: type 2 diabetes mellitus without complications.

Lookup: CMS ICD-10

Watch for: If a diagnosis label is unfamiliar or appears inconsistent with your records, ask the provider to explain it. The code and bill alone do not prove the diagnosis or coding was wrong.

ICD-10-PCS

Inpatient procedure codes used by hospitals for services delivered during an inpatient stay.

ICD-10-PCS is hospital-only. If you were admitted as an inpatient, the procedures performed during the stay are coded in ICD-10-PCS rather than CPT. The codes are seven characters long and describe the procedure in structured detail.

Example: ICD-10-PCS 0FT44ZZ: laparoscopic resection of the gallbladder.

Lookup: CMS ICD-10-PCS

Watch for: A character can change the procedure represented and may affect claim classification. Ask the hospital or payer to explain any unfamiliar code; do not infer an error from the code alone.

NDC (National Drug Code)

The current FDA-assigned NDC is a unique 10-digit, three-segment number identifying the labeler, product, and trade package size.

Current FDA formats are 4-4-2, 5-3-2, or 5-4-1. Some reimbursement transactions display a HIPAA-standard 11-digit form created by padding a segment with a leading zero. FDA's uniform 12-digit format takes effect March 7, 2033.

Example: Neutral 4-4-2 format example: 0000-0000-00 (labeler-product-package). This illustrates the 10-digit, three-segment format and is not a drug lookup.

Lookup: FDA National Drug Code format

Watch for: Confirm which NDC format the document uses, then compare the labeler, product, package, and quantity with the source record. Ask the provider, pharmacy, or payer to explain a mismatch rather than treating it as proof of an incorrect charge.

DRG (Diagnosis-Related Group)

A classification used to set a fixed payment amount for an inpatient hospital stay, based on diagnoses and procedures.

Medicare uses MS-DRGs for many inpatient prospective payments, and some other payers use DRG-based methods. The assigned group can depend on diagnoses, procedures, patient characteristics, discharge status, and payer-specific rules.

Example: MS-DRG 470: major hip and knee joint replacement without major complications.

Lookup: CMS MS-DRG

Watch for: Itemized charges and the plan's calculated payment can differ substantially. Compare the EOB with the itemized bill and ask the hospital or payer which payment method applied.

Modifiers

Two-character additions to a CPT or HCPCS code that change its meaning without changing the underlying procedure code.

Modifiers describe circumstances that affect payment: which side of the body, whether the service was bilateral, whether it was a separately identifiable service from another billed on the same day, and so on.

Example: Modifier 50: bilateral procedure. Modifier 25: significant, separately identifiable evaluation and management service on the same day as a procedure.

Lookup: CMS modifier reference

Watch for: A modifier can materially affect processing. Ask which circumstance and documentation supported an unfamiliar modifier; the bill alone cannot show whether its use was appropriate.

Place of Service codes

Two-digit codes that indicate where the service was delivered.

Payers can process the same procedure differently by setting. Under the CMS code set, Place of Service 11 is office, 22 is on-campus outpatient hospital, and 21 is inpatient hospital. Other payment and facility-charge rules vary.

Example: POS 22: on-campus outpatient hospital under the CMS place-of-service code set.

Lookup: CMS Place of Service code set

Watch for: If the setting differs from what you expected, ask whether a facility charge or different payment rule applied and compare the EOB with advance notices and the provider bill.

Revenue codes

Four-digit codes used on the UB-04 hospital claim form to group charges by department or category.

Revenue codes describe the type of service or department the charge came from: room and board, pharmacy, operating room, lab, and so on. They are paired with HCPCS or CPT codes that describe the specific service.

Example: Revenue code 0450: emergency room, general classification. Revenue code 0250: pharmacy.

Lookup: NUBC overview (publishers of UB-04)

Watch for: Ask about a department category that does not match your records or a pharmacy category that lacks enough detail to identify what was administered.

EOB and billing abbreviations

These acronyms appear repeatedly across bills, EOBs, and insurance correspondence. Knowing what each one means makes the rest of the document readable.

EOB

Explanation of Benefits, the insurer's record of how a claim was processed. Not a bill.

COB

Coordination of Benefits, the rules that determine which plan pays first when you have more than one insurance.

AOB

Assignment of Benefits, an authorization that lets the provider receive payment directly from the insurer.

DOS

Date of Service, the date the care was actually delivered.

POS

Place of Service code, indicating where care was delivered (office, outpatient hospital, inpatient hospital, etc.).

PCP

Primary Care Provider. A plan may designate a PCP and may require referrals for some services; check the plan.

PPO

Preferred Provider Organization. Network, referral, and out-of-network benefits depend on the specific plan.

HMO

Health Maintenance Organization. Network and referral rules depend on the plan and exceptions.

EPO

Exclusive Provider Organization. Network and referral rules depend on the plan.

POS plan

Point of Service plan. In-network, referral, and out-of-network terms depend on the plan.

Deductible

The amount a member pays for covered services before the plan pays for services subject to the deductible; some benefits may apply before it is met.

Copay

A fixed amount a plan may apply as cost sharing for a covered visit, service, or item; the amount and conditions depend on the plan.

Coinsurance

Plan-calculated percentage cost sharing for a covered service under the plan's terms, often applied to the allowed amount after an applicable deductible.

OOP max

Out-of-pocket maximum, a plan-year limit on eligible cost sharing for covered services. Check what the plan excludes.

Allowable / Allowed Amount

The amount the plan treats as eligible when calculating benefits. It is not always the amount the plan pays or the amount the patient legally owes.

Adjustment / Write-off

A reduction or adjustment shown during claim processing. Ask the provider and plan whether the patient owes any part of it.

N/C (Non-covered)

A label that may indicate the plan treated all or part of an item as non-covered. Check the reason code, plan terms, and appeal notice.

N/A

Not applicable, often used in EOB columns where a value would not make sense for that line.

Pending

The claim has not finished processing yet.

Paid

The insurer has paid its portion of the claim.

Denied

The plan did not pay all or part of a claim. The notice should identify the reason and applicable review or appeal instructions.

Appealed

A formal request to reconsider an adverse benefit decision. Follow the deadline and method in the plan's notice.