ICD codes are the standardized numbers doctors use to record your diagnosis in medical records, insurance claims, and billing

An ICD code is a short alphanumeric label — usually starting with a letter followed by numbers and sometimes a decimal point — that identifies a specific medical condition. Your doctor doesn't invent these codes; they come from an official list maintained by the World Health Organization and adopted by the U.S. healthcare system. When your rheumatologist documents that you have osteoarthritis of the knee, they record it using an ICD code so that every clinic, hospital, pharmacy, and insurance company you visit reads the same diagnosis the same way.

For arthritis, you will see codes that start with M (the letter used for diseases of the musculoskeletal system). A code like M17.11 means osteoarthritis of the right knee; M19.90 means unspecified osteoarthritis of an unspecified site. Rheumatoid arthritis uses codes starting with M05 or M06. These codes appear on every bill your insurance receives, on referral letters to specialists, and in your medical record at every provider you see.

Understanding what your ICD code means matters because it affects how your care is documented, how your insurance processes claims, and what information follows you between providers. If a code is wrong — if it says you have arthritis in your left shoulder when you actually have it in your right — that error can delay treatment, confuse a new doctor, or cause a claim to be denied.

Key Takeaways

  • ICD codes are standardized diagnosis labels used by all U.S. healthcare providers, insurers, and billing systems so your condition is recorded the same way everywhere.
  • Arthritis codes begin with M and include specific details like which joint is affected and which side of your body, so M17.11 (right knee osteoarthritis) is different from M17.12 (left knee osteoarthritis).
  • You can find your ICD code on any bill, explanation of benefits, or medical record summary your provider sends you.
  • If you believe your ICD code is incorrect, contact your doctor's billing office or medical records department to request a correction before it spreads to other providers and insurers.

How ICD codes are assigned to arthritis diagnoses

Your doctor assigns an ICD code based on what type of arthritis you have, which joints are affected, and how advanced it is. The assignment happens during or after your visit: the doctor documents your diagnosis in plain language (for example, "osteoarthritis of both knees"), and then the medical coder or billing staff translates that into the corresponding ICD code. In many modern practices, the doctor selects the code directly from a dropdown menu in the electronic health record, which speeds up the process but also means the code is only as accurate as the information the doctor entered.

The specificity of ICD codes has grown over time. Older versions required only a general code like "osteoarthritis." Current codes (called ICD-10, adopted in the U.S. in 2015) demand much more detail: which joint, which side of the body, and sometimes whether other joints are also affected. This precision helps researchers track disease patterns and helps insurers understand the true cost of care, but it also means your code can be wrong if your doctor didn't document which knee hurts or whether you have arthritis in one hand or both.

If you see multiple doctors for your arthritis — a primary care physician, a rheumatologist, and perhaps an orthopedic surgeon — each one may assign a code during their visit. These codes should match, but they don't always. A primary care doctor might code your condition as "arthritis, unspecified site" while your rheumatologist codes it as "rheumatoid arthritis with involvement of multiple sites." The more specific code (the rheumatologist's) is usually the one that should be used going forward, but the mismatch can cause confusion in your records.

Where you will see your ICD code

Your ICD code appears on several documents you receive from your healthcare providers and insurance company. On an explanation of benefits (the form your insurance sends after a claim is processed), the code is listed next to the service you received — for example, "Office visit for arthritis management, code M19.90." On a medical record summary or discharge paper from a hospital or clinic, your diagnosis is listed with its code. On a referral letter to a specialist, your primary care doctor includes the code so the specialist knows exactly what condition you were referred for.

You can also find your code by asking your doctor's office directly. Call the billing or medical records department and ask, "What ICD code is used for my arthritis diagnosis?" They can tell you over the phone or send it to you in writing. If you use an online patient portal (many large health systems offer these), you may be able to view your diagnosis codes by looking at past visit summaries or your problem list.

Insurance companies use ICD codes to decide whether to cover a treatment. If your insurance receives a claim with a code that doesn't match their coverage rules for that code, they may deny the claim or ask for more information. For example, if your doctor prescribes a biologic medication for rheumatoid arthritis but the code submitted is for osteoarthritis, the insurance company may reject the claim because biologics are not covered for osteoarthritis under most plans.

Common ICD codes for different types of arthritis

Osteoarthritis codes start with M17 (knee), M18 (hand), M19 (other sites), or M15 (multiple sites). The most common code is M17.11 or M17.12 (osteoarthritis of the right or left knee). Rheumatoid arthritis codes start with M05 or M06, with additional digits specifying which joints are involved and whether the disease is active. Gout uses codes starting with M10. Lupus-related arthritis falls under the broader lupus codes (L93 or M32). Psoriatic arthritis uses codes starting with L40.5.

Within each category, the code becomes more specific with each digit. For osteoarthritis of the knee, M17.1 means one knee is affected, but M17.11 specifies the right knee and M17.12 specifies the left knee. If both knees are affected, the code is M17.0. If you have osteoarthritis in multiple different joints (knees, hips, hands), your doctor may use a code from the M15 category instead, which captures polyosteoarthritis.

You don't need to memorize these codes, but knowing that your code starts with M17 tells you that your diagnosis is recorded as knee osteoarthritis, and knowing the last digit tells you which side. If you see a code that doesn't match what you understand your diagnosis to be, that's a sign to ask your doctor for clarification.

What happens if your ICD code is wrong

An incorrect ICD code can cause real problems. If your code says you have osteoarthritis when you actually have rheumatoid arthritis, your insurance may deny coverage for medications that are only approved for rheumatoid arthritis. If the code says your arthritis is in your left knee but it's actually in your right knee, a surgeon or physical therapist might prepare to treat the wrong side. If the code is too vague (arthritis, unspecified site), your insurance may request more information before processing a claim, which delays payment to your provider and can delay your own care.

Errors also accumulate. Once a code is recorded in your medical record, it tends to be copied forward to every future visit. A new doctor sees the code in your chart and assumes it's correct. The code gets sent to specialists you're referred to. Your insurance company's system flags you as having that diagnosis for coverage decisions. Correcting an error after it's been in the system for months or years is possible but requires active effort.

If you believe your code is wrong, contact your doctor's office and ask to speak with the billing department or medical records department. Explain what you believe the error is — for example, "My code says left knee, but I have arthritis in my right knee" — and ask them to review your chart and correct it if needed. Request written confirmation of the correction. If the error affects a claim that was already denied, ask your insurance company to reprocess the claim with the corrected code.

How to read your own ICD code

ICD-10 codes (the current system in the U.S.) follow a pattern: a letter, followed by two digits, then a decimal point, then one to two more characters. The letter indicates the broad category of disease (M for musculoskeletal, for example). The first two digits narrow it down further (17 for knee osteoarthritis). The digits after the decimal point add specificity: which side, how severe, or which joints are involved.

To decode your code, start with the letter and first two digits. Look up what that combination means — M17 is osteoarthritis of the knee. Then look at the digits after the decimal. The first digit after the decimal usually specifies which side: 1 for right, 2 for left, 9 for unspecified. The second digit (if present) may indicate severity or other details. So M17.11 reads as "osteoarthritis of the right knee," and M17.92 reads as "unspecified osteoarthritis of the left knee."

You can look up any ICD code online using the Centers for Medicare & Medicaid Services (CMS) ICD-10 code search tool on their website, or using other free medical coding databases. Type your code into the search box and you'll see the full description. This is useful if you receive a code on a bill or in a medical record and want to understand exactly what it means.

ICD codes and your insurance coverage

Insurance companies use ICD codes to determine whether a treatment, medication, or procedure is covered under your plan. Your insurance policy includes a list of covered treatments for each diagnosis code. If your doctor prescribes a treatment that isn't on the covered list for your code, your insurance may deny the claim. This is one reason why having the correct code matters: if you have rheumatoid arthritis but your code says osteoarthritis, your insurance might deny a biologic drug that would be covered if the code were correct.

Some insurance plans also use ICD codes to set limits on how often you can receive a service. For example, physical therapy might be covered up to 30 visits per year for osteoarthritis but unlimited for rheumatoid arthritis. The code determines which limit applies to you. Similarly, some medications require prior authorization (approval from the insurance company before you fill the prescription), and whether authorization is required often depends on your diagnosis code.

If your insurance denies a claim and you believe the denial is based on an incorrect code, ask your doctor's office to submit the claim again with the correct code. If you believe the code is correct but the insurance company is still denying coverage, ask your doctor to contact the insurance company's medical review department to appeal the denial. Your doctor can explain why the treatment is medically necessary for your specific diagnosis.

Frequently Asked Questions

Can I change my ICD code if I disagree with my diagnosis?

No, you cannot change your code yourself, and the code reflects your doctor's medical judgment, not your preference. If you disagree with your diagnosis, discuss it with your doctor. If your doctor agrees the diagnosis is wrong, they will update it in your medical record and a new code will be assigned. The code is a medical record, not a billing preference.

Do I need to tell a new doctor what my ICD code is?

No. Your new doctor will review your medical records, which include your diagnosis and code, and will assign their own code based on their examination and your history. You don't need to memorize or recite your code. If you want to know what code is being used, you can ask the new doctor's office after your visit.

What if I have arthritis in multiple joints — will I have multiple codes?

You may have one code that covers multiple joints (like M15 for polyosteoarthritis) or multiple separate codes if different types of arthritis affect different areas. Your doctor decides how to code your condition based on what they document. If you're unsure whether your multiple joint problems are all captured in your codes, ask your doctor's billing office to list all the diagnosis codes on your account.

Does my ICD code affect my life insurance or disability insurance?

Your medical records, including your diagnosis and ICD code, may be reviewed if you explore for life insurance or disability insurance. The code itself doesn't determine coverage, but it's part of your medical history that insurers consider. Be honest with your doctor about your symptoms so your diagnosis and code are accurate, as this supports any future insurance claim you might need to make.

Will my ICD code change if my arthritis gets worse?

Your code may be updated if your condition changes significantly. For example, if your osteoarthritis progresses to the point where you need joint replacement surgery, your doctor might add or change codes to reflect the severity. Codes can also change if you develop a new type of arthritis or if your original diagnosis was revised. Your doctor updates the code based on what they observe at each visit.