Learn About Insurance Codes to Avoid Billing Errors

Mistakes in coding can cost you money

Insurance codes are used by your health plan to make decisions about your prior authorization requests and claims, and to determine how much to pay your healthcare providers. Typically, you will see these codes on your Explanation of Benefits and medical bills.

Medical bills and insurance claim form
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An Explanation of Benefits (EOB) is a form or document that may be sent to you by your insurance company several weeks after you had a healthcare service that was paid by the insurance company.

Your EOB is a window into your medical billing history. Review it carefully to make sure you actually received the service being billed, the amount your healthcare provider received and your share are correct, and that your diagnosis and procedure are correctly listed and coded.

Importance of Insurance Codes

EOBs, insurance claim forms, and medical bills from your healthcare provider or hospital can be difficult to understand because of the use of codes to describe the services performed and your diagnosis. These codes are sometimes used instead of plain English, although most health plans use both codes and written descriptions of the services included on EOBs, so you'll likely see both. Either way, it's useful for you to learn about these codes, especially if you have one or more chronic health problem.

For example, millions of Americans have type 2 diabetes along with high blood pressure and high cholesterol. This group of people is likely to have more health services than the average American and, therefore, will need to review more EOBs and medical bills.

Coding Systems

Health plans, medical billing companies, and healthcare providers use three different coding systems. These codes were developed to make sure that there is a consistent and reliable way for health insurance companies to process claims from healthcare providers and pay for health services.

Current Procedural Terminology

Current Procedural Terminology (CPT) codes are used by healthcare providers to describe the services they provide. Your healthcare provider will not be paid by your health plan unless a CPT code is listed on the claim form. You may see CPT referred to as CPT-4; this is because the current version of CPT is the 4th edition.

CPT codes are developed and updated by the American Medical Association (AMA). Unfortunately, the AMA does not provide open access to the CPT codes. Medical billers who use the codes must purchase coding books or online access to the codes from the AMA.

The AMA site allows you to search for a code or the name of a procedure. However, the organization limits you to no more than five searches per day (you have to create an account and sign in to be able to use the search feature).

Also, your healthcare provider may have a sheet (called an encounter form or "superbill") that lists the most common CPT and diagnosis codes used in her office. Your healthcare provider's office may share this form with you.

Some examples of CPT codes are:

  • 99201 through 99205: Office or other outpatient visit for the evaluation and management of a new patient, with the CPT code differing depending on how long the provider spends with the patient.
  • 93000: Electrocardiogram with at least 12 leads.
  • 36415: Collection of venous blood by venipuncture (drawing blood).

Healthcare Common Procedure Coding System

The Healthcare Common Procedure Coding System (HCPCS) is the coding system used by Medicare. Level I HCPCS codes are the same as the CPT codes from the American Medical Association.

Medicare also maintains a set of codes known as HCPCS Level II. These codes are used to identify products, supplies, and services that aren't covered under CPT codes, including ambulance services and durable medical equipment (wheelchairs, crutches, hospital beds, etc.), prosthetics, orthotics, and supplies that are used outside your healthcare provider's office.

Some examples of Level II HCPCS codes are:

  • L4386: Walking splint
  • E0605: Vaporizer
  • E0455: Oxygen tent

The Centers for Medicare and Medicaid Services maintains a website where updated HCPCS code information is available to the public.

International Classification of Diseases

The third system of coding is the International Classification of Diseases, or ICD codes. These codes, developed by the World Health Organization (WHO), identify your health condition, or diagnosis.

ICD codes are often used in combination with the CPT codes to make sure that your health condition and the services you received match. For example, if your diagnosis is bronchitis and your healthcare provider ordered an ankle X-ray, it is likely that the X-ray will not be paid for because it is not related to bronchitis. However, a chest X-ray is appropriate and would be reimbursed.

The current version is the 10th revision, or ICD-10, which has been in use in many countries since the mid-1990s. It will be replaced by ICD-11 as of 2022.

Some examples of ICD-10 codes are:

  • E66.0: Obesity due to excess calories
  • F32.0: Mild depression
  • S93.4: Sprained ankle

A complete list of diagnostic codes (known as ICD-10) is available to download from the CMS website, and ICD10data.com makes it fairly straightforward to search for various codes.

The U.S. transitioned from ICD-9 to ICD-10 codes in 2015, but the rest of the world's modern healthcare systems had implemented ICD-10 many years earlier. CPT codes continue to be used in conjunction with ICD-10 codes (they both show up on medical claims), because CPT codes are for billing, whereas ICD-10 codes are for documenting diagnoses.

Coding Errors

Using the three coding systems can be burdensome to a practicing healthcare provider and busy hospital staff and it is easy to understand why coding mistakes happen. Because your health plan uses the codes to make decisions about how much to pay your healthcare provider and other healthcare providers, mistakes can cost you money.

A wrong code can label you with a health-related condition that you do not have, result in an incorrect reimbursement amount for your healthcare provider, potentially increase your out-of-pocket expenses, or your health plan may deny your claim and not pay anything.

It's possible for your healthcare provider, the emergency room, or the hospital to miscode the services you received, either coding the wrong diagnosis or the wrong procedures. Even simple typographical errors can have significant consequences.

Example of Coding Error

Doug M. fell while jogging. Because of pain in his ankle, he went to his local emergency room. After having an X-ray of his ankle, the ER physician diagnosed a sprained ankle and sent Doug home to rest.

Several weeks later Doug got a bill from the hospital for more than $500 for the ankle X-ray. When his EOB arrived, he noticed that his health plan had denied the X-ray claim.

Doug called his health plan. It took a while to correct an error made by the billing clerk in the emergency room. She accidentally put a wrong number in Doug's diagnosis code, changing S93.4 (sprained ankle) to S53.4 (sprained elbow).

Doug's health plan denied the claim because an X-ray of the ankle is not a test that is performed when someone has an elbow injury.

A Word From Verywell

There are several steps in the process of filling out and submitting a medical claim. Along the way, the humans and computers involved in the process can make mistakes. If your claim has been denied, don't be shy about calling both your healthcare provider's office and your health plan.

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9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Medical Association. CPT Purpose and Mission.

  2. American Medical Association. Finding coding resources.

  3. Medicare Payment, Reimbursement, CPT Code, ICD, Denial Guidelines. CPT Code — 99201, 99202, 99203, 99204, 99205 — Office Visit Code.

  4. Find-A-Code. CPT 93000 in section: Electrocardiogram, routine ECG with at least 12 leads.

  5. Dowling, Renee. Medical Economics. How to Properly Document and Bill for Venipuncture. August 1, 2018.

  6. Centers for Medicare and Medicaid Services. HCPCS Coding Questions.

  7. Centers for Medicare and Medicaid Services. HCPCS quarterly update. Updated May 20, 2021.

  8. World Health Organization. WHO Releases New International Classification of Diseases (ICD 11). June 18, 2018.

  9. Hirsch JA, Nicola G, Mcginty G, et al. ICD-10: History and context. AJNR Am J Neuroradiol. 2016;37(4):596-9. doi:10.3174/ajnr.A4696

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