"Code First" rules (ICD-10)


About Code First

"Code First" is a rule that applies to diagnoses that require a primary diagnosis to be listed first. Most Code First rules occur in diagnoses that state clearly the need or in which there is a known etiology and manifestation connection. 

The Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS) as part of the Department of Health and Human Services provide the guidelines for coding and reporting using ICD-10.

Specific Conventions within ICD-10 are reviewed regularly for clinical appropriateness.


Why this change is being made

We made this change in order to become compliant with coding and reporting requirements. As payers update both their policies and their claims processing software, we’ll see more payers citing Code First rules for claim denials.

Although payers may have paid some of these claims, these Code first requirements are not new; 
a primary diagnosis is required to be listed first per this rule. Insurance companies may or may not “catch” this error during initial claims processing.

If they catch the error, they will deny the claim.

If they don’t catch the error, they might never “reverse the decision.” However, these claims are at risk for review– sometimes years after the date of service.


What happens to previous claims that were denied for Code First

If you have had denied claims as a result of Code First rules, we may reach out to and ask what diagnoses you would like to use as the primary diagnosis and resubmit your claims.

Ideally, with the Code First rules in place we will prevent discrepancies rather than correct them.


Determining the appropriate diagnosis 

When you choose a code that has a “Code First” rule applied to it, you will be given a list of physiological conditions that can be used as a first listed Code.

These codes have been either suggested by the ICD-10 guidelines or listed because of input from other MDs.


Frequently asked questions

Will the insurance company be suspicious if I change my diagnosis for a regular client?

No, insurance companies will not be suspicious if you change the diagnosis code for a regular client. As you work with a client you often will gain insight which will result in clarity and more specificity for a diagnosis code. There are also other reasons and presentations that may contribute to a change of codes.

In this case, the primary codes that are required in the Code First rules are being looked for by the insurance companies.


What are the benefits of coding according to the ICD-10 rules?

Using the ICD-10 enables greater specificity in identifying mental health conditions. It also provides better data for measuring and tracking mental health care utilization and the quality of patient care.

This means that:

  • You'll have fewer denials.
  • As you work within the ICD-10 rules, your sessions are billed “cleaner” and there will be fewer requests for notes or additional information from the insurance companies.


What changed? 

Nothing! If you are not an MD or NP, you may need to check or request documentation of lab findings, tests, or clinical documentation of other providers, in order to properly use these diagnoses identified as a physiological condition.



Some conditions have both an underlying etiology and a manifestation, both of which are coded according to the etiology/manifestation convention. This is the reasoning behind Code First rules.  

An example in which the etiology/manifestation combination is signaled in this way can be found in many of the categories under Mental Disorders Due to Known Physiological Conditions (F01–F09), including the subcategory Other Mental disorders due to known physiological condition (F06).  

For Example

F06.30 - Mood disorder due to known physiological condition, unspecified.

For this diagnosis, the mood disorder is unspecified but it is due to “known physiological condition”. So, in this case, the physiological condition must be listed (coded) first.

An example of Parkinson’s Disease as the “physiological condition known” for the unspecified mood disorder would be listed as G20, F06.30.

The Parkinson’s disease diagnosis must be listed (coded) first, followed by the F06.30 Diagnosis.  

In the ICD-10 guidelines when you look up Parkinson’s disease and you go to code G20 it says G20 should be first listed and it indicates that you should “Use additional code(s)...”

If there is not a known physiological condition for the Mood disorder, you would choose a Diagnosis from the Mood Disorders, not due to a known physiological condition (F30-F34.F39).  That code would be listed without the physiological condition.  



This document is intended for educational purposes only. It is designed to facilitate compliance with payer requirements and applicable law, but please note that the applicable laws and requirements vary from payer to payer and state to state. Please check with your legal counsel or state licensing board for specific requirements.

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