When your doctor bills your insurance, they don't describe your visit in plain language — they use standardized codes to represent individuals procedures and medical service provided. These codes tell insurers exactly what was diagnosed, what was done, and what equipment or supplies were used. At BillCare, we work with four main code types to review your bills for errors.

TLDR; Reference the end of this guide to find a list of the most commonly used healthcare codes and their significance

The 4 Most Commonly Used Codes:

1. CPT (Current Procedural Terminology) Codes — What the doctor did

CPT codes are the most common codes you'll see on a bill. They cover outpatient procedures, office visits, tests, and treatments. Each code is a five-digit number maintained by the American Medical Association.

CPT codes fall into three categories:

• Category I — Standard procedures and services (the vast majority of codes)

• Category II — Supplemental codes used for tracking quality of care

• Category III— Temporary codes for emerging or experimental procedures

Common examples: Standard office visit, EKG, knee steroid injection

2. HCPCS (Healthcare Common Procedure Coding System) Level II Codes — What was used

Where CPT codes describe procedures, HCPCS Level II codes cover the products and services that don't fit neatly into CPT — things like medical equipment, supplies, ambulance transport, and medications that can't be self-administered.

Common examples: Crutches, ambulance transport, home oxygen equipment

A quick way to remember the difference: CPT = what was done. HCPCS = what was used.

3. ICD-10-CM Codes — What the diagnosis was

International Classification of Diseases, Clinical Modification

These are diagnosis codes — they tell your insurer what condition you had. You'll find them on your doctor's notes, your claim, and your Explanation of Benefits (EOB). They're required for virtually all insurance billing in the U.S.

Common examples: Influenza, ankle sprain, headache

4. ICD-10-PCS (International Classification of Diseases, Clinical Modification) Codes — What happened during a hospital stay

These codes are used exclusively for inpatient (overnight) hospital procedures — not outpatient visits. Each code is seven characters long and encodes very specific details about what was done, where, and how.

Example: Appendix removal, heart transplant, gallbladder resection

If you were never admitted overnight, you won't see these on your bill.

Other Codes You May Encounter:

Mental Health — DSM-5 codes are used alongside ICD-10-CM for behavioral and psychiatric diagnoses (e.g., Generalized Anxiety Disorder → F41.1).

Dental — CDT codes cover dental procedures. Teeth are also identified by number using the Universal Numbering System (e.g., Tooth #30 = lower right molar).

Pharmacy — NDC (National Drug Code) codes identify specific medications and dosages. These are useful for verifying you were billed for what you actually received.

Lab Tests — LOINC codes identify specific laboratory tests (e.g., fasting blood glucose → 1558-6).

Revenue Codes identify where a service took place within a hospital — the emergency room, lab, pharmacy, etc. They appear on inpatient and outpatient hospital bills (eg. emergency room, lab services, pharmacy)

Modifiers are two-character additions to CPT or HCPCS codes that add important context — for example, whether a procedure was performed on the left or right side of the body, or whether two separate services were delivered in the same visit (eg. 25, LT, RT)

Modifiers matter because a missing or incorrect modifier can cause a valid claim to be denied.

Why This Matters:

You don't need to memorize these codes — but knowing they exist helps you catch errors. A wrong code can mean your insurer denies a valid claim, or that you're billed for something you never received. When BillCare reviews your bill, this is exactly what we're looking for.

Helpful resources if you want to look up a code yourself:

• findacode.com — Free code lookup

• cms.gov — Official Medicare coding guidance

• goodrx.com — NDC codes and drug pricing

Quick Reference: Common Medical Codes Masterlist

Save this to your documents to serve as a quick reference of the most commonly used codes:

CPT Codes — What the Doctor Did

HCPCS Level II Codes — What Was Used

ICD-10-CM Codes — What the Diagnosis Was

ICD-10-PCS Codes — What Happened During a Hospital Stay

Revenue Codes — Where It Happened

Modifiers — Additional Context on a Service