Diagnosis Codes: The Foundation of Your Medical Claim

October 9, 2018

Updated 12/2025

You know that feeling.

You’ve done everything right for your patient.
You’ve performed the procedure, documented the visit, pored over the chart, carefully selected the CPT code that perfectly reflects your work…

You hit “submit” on the claim and wait.

Weeks go by.

Then the notice hits your inbox: Denied. 

Not for lack of treatment. Not because the CPT code was “wrong.”

More often than most practices realize, the problem was hiding in plain sight:

Your diagnosis codes didn’t tell the story. 

The Most Overlooked Part of Your Claim

In many offices, procedure codes get all the attention.

Teams will debate which CPT code best matches the service. They’ll attend trainings, read payor guidelines, and agonize over tiny details to get that part “perfect.”

And then, in the final stretch, when it’s time to enter diagnosis codes?

• A few “old faithful” codes get thrown in.
• The same handful you’ve used a hundred times.
  • “Impacted tooth.”
  • “Jaw pain.”
  • “Cracked tooth.”

Click. Send.

And when the denial comes back, everyone stares at the CPT codes…when the real issue may be that your ICD codes never justified why those procedures were medically necessary.

Medical insurers often see only what’s on the claim form. If the diagnosis codes don’t clearly support the procedures, your claim may be weakened from the start.

Diagnosis Codes Are the Foundation, Not an Afterthought

Think of the claim like a building:

• CPT codes are the visible structure – the walls, the roof, the finishes.
• Diagnosis codes are the foundation and support beams –  the reason the structure stands at all.

If the foundation is weak, it doesn’t matter how beautiful the rest of the building is.

What Strong Diagnosis Coding Actually Looks Like

A strong set of diagnosis codes should describe the main problem clearly.

Primary Conditions That Define the Problem

• Missing teeth
• Severe decay
• Cracked or fractured tooth
• Trauma
• Cysts or lesions

Secondary Symptoms That Show Patient Impact

Capture secondary symptoms that show the impact on the patient’s life. These are often overlooked but incredibly powerful:

• Jaw pain
• Temporomandibular dysfunction
• Headaches
• Migraines
• Facial pain

Comorbidities That Support Medical Necessity

Include comorbidities that increase risk or complexity. These aren’t “extra” – they can be critical support for medical necessity:

• History of cancer
• Radiation or chemotherapy
• GERD
• Ulcers
• Sjögren’s syndrome

Other systemic conditions impacting healing, infection risk, or treatment decisions

Accident and Trauma Context When Applicable

Use accident/trauma codes when applicable. If treatment is needed because of an accident, your diagnosis coding should reflect:

What happened (fall, motor vehicle accident, sports injury, assault, etc.)

Where and how it occurred (when supported by proper codes and documentation)

There are tens of thousands of diagnosis codes available because real patients are complicated. A single code rarely tells the full story.

Why Diagnosis Codes Matter So Much to Payors

From the payor’s perspective, the claim form is often the first and primary window  into:

• What’s wrong with the patient
• How serious it is
• Why your chosen procedures are necessary right now
• Why alternatives (or no treatment) are not appropriate

Yes, carriers can request clinical records.
Yes, you can choose to send chart notes and imaging.

But when it comes to medical claims, in many cases, the initial judgment on your claim is made based on what’s already on the claim form- and that means your diagnosis coding is doing the heavy lifting.

When CPT Codes Are Right, but Claims Still Get Denied

If your claim only says, “Cracked tooth” + a complex procedure code”…you may not be showing the full picture.

If instead, your diagnosis coding reflects:

• Cracked tooth
• Severe pain
• Jaw dysfunction
• History of radiation treatment
• Dry mouth due to Sjögren’s

…you’re not just submitting a claim. You’re presenting a medical argument for necessity.

The Real Cost of Diagnosis-Driven Denials

Every denied claim is more than a line item.

• It’s frustration for your billing team.
• It’s cash flow interruption for your practice.
• It’s stress and confusion for patients who trusted you to guide them.
• It’s extra time appealing and resubmitting when you should be focused on care.

And what’s especially painful?

Knowing that some of those denials could potentially have been avoided with more precise diagnosis coding, without changing a single thing about the care you provided.

What to Do Before You Submit Your Next Claim

You don’t have to overhaul your entire process overnight. Start with a few powerful habits:

1. Treat diagnosis coding as clinical storytelling. 

Before you submit, ask:

“If someone only saw these diagnosis codes, would they understand why this procedure is needed?”

If the answer is “not really” or “only partly,” there’s room to improve.

2. Read the chart notes like an auditor.

Don’t just glance. Really review:

• What symptoms did the patient report?
• What did the exam reveal?
• What risk factors or comorbidities existed?
• Was trauma involved? How? When?

Every clinically relevant detail you see in the chart is a potential diagnosis code –  if there is an appropriate, supported code and it’s allowed by payor guidelines.

3. Use every applicable diagnosis code (within guidelines). 

If it’s documented, relevant, and supported, don’t be shy about using it.

• Primary diagnosis: the main reason for the procedure
• Secondary diagnoses: symptoms, complications, or related conditions
• Comorbidities: systemic issues that impact treatment, healing, or risk
• Accident/trauma codes: where appropriate and documented

This doesn’t mean “throw codes at the wall.” It means coding thoughtfully and completely.  

4. Train your team to stop “rushing through” this step. 

Diagnosis coding shouldn’t be the two-minute task you squeeze in at the end.

Make it a standard, deliberate step in your workflow – not an afterthought.

A Simple Diagnosis Coding Challenge

For your next five claims: 

1. Read the chart notes as if you were the insurance reviewer.
2. List every documented, relevant condition and symptom.
3. Compare that list to the diagnosis codes you initially planned to use.
4. Ask: “Does this coding fully support the procedures I’m billing for?”

You may be surprised at how often important pieces of the story were missing from your claim.

Diagnosis codes are not just “extra boxes” on a form. They are the foundation of your medical claim and often the first proof of medical necessity that a payor ever sees.

When you treat them with the same care and intention as your CPT codes, you give your claims – and your patients –  the support they deserve.

How eAssist Strengthens Medical Claims

If reading this made you realize how much diagnosis coding has been costing your practice in lost revenue, delayed payments, and endless appeals, you don’t have to fix it alone.

This is exactly where eAssist excels. 

At eAssist, our medical billers don’t just “file claims.”
We analyze, optimize, and elevate your coding and documentation so your claims tell the full story – the story that gets paid.

• We help identify missed or underused diagnosis codes.
• We build stronger medical necessity justification.
• We reduce preventable denials.
• We give you back the time to focus on patient care, not paperwork.

If you’re ready for cleaner claims, faster approvals, and more predictable revenue, we’re here to help. Schedule a consultation and see how much stronger your medical billing process can be. Let’s build claims that get approved the first time.

Disclaimer: Insurance administration and dental billing recommendations presented here represent the opinions of the author or our staff and are for informational purposes only. You are responsible for your own use of the CDT Codes, insurance administration, and dental billing. For the latest CDT codes and official interpretations, contact the American Dental Association or visit ADA.org.