ICD-10-CM 2025 Updates & Guidelines: What CPC Candidates Must Know

The fiscal year 2025 ICD-10-CM code set represents one of the most significant annual updates to diagnosis coding in recent years, with 324 new codes, 36 deletions, and 13 revisions effective October 1, 2024. For CPC exam candidates and practicing medical coders, understanding these changes is not just about compliance—it's about demonstrating the coding precision that employers demand and that the CPC certification validates.

This comprehensive guide covers everything you need to know about the 2025 ICD-10-CM updates, from major code additions in obesity and hypoglycemia classifications to critical guideline changes that affect daily coding practice.

Overview of FY 2025 Updates

The Centers for Disease Control and Prevention (CDC) and Centers for Medicare & Medicaid Services (CMS) released the FY 2025 ICD-10-CM updates on July 3, 2024—slightly later than the typical June release. These changes became effective for all healthcare encounters occurring on or after October 1, 2024, and remain in effect through September 30, 2025.

The 2025 updates continue the ICD-10-CM's evolution toward greater specificity, particularly in areas where clinical practice has advanced significantly. The most substantial changes occur in endocrine disorders (particularly obesity and diabetes-related hypoglycemia), mental health conditions (eating disorders), and oncology (lymphoma remission status).

Key Themes in 2025 Updates

Several overarching themes characterize the 2025 code set updates:

• Increased Specificity: Many existing parent codes have been expanded with additional character requirements to capture greater clinical detail
• Value-Based Care Alignment: New codes support quality measurement and risk adjustment in value-based payment models
• Clinical Practice Evolution: Updates reflect current diagnostic terminology and treatment approaches
• Social Determinants of Health: Expanded Z codes address healthcare access barriers and social factors
• Research Support: Enhanced granularity enables more precise clinical research and epidemiological tracking

Major Update: Obesity Classification Codes (E66.81-)

One of the most clinically significant additions for 2025 is the expansion of subcategory E66.8 (Other obesity) to include obesity class codes based on Body Mass Index (BMI) classifications. These changes reflect the growing medical recognition of obesity as a complex, multifactorial condition requiring nuanced coding.

New Obesity Class Codes

Code	Description	BMI Range
E66.81	Obesity class (parent code - not billable)	N/A
E66.811	Obesity class 1	BMI 30-34.9 kg/m²
E66.812	Obesity class 2	BMI 35-39.9 kg/m²
E66.813	Obesity class 3 (severe obesity)	BMI ≥40 kg/m²

Coding Guidelines for Obesity Class Codes

The new Coding Guidelines section I.C.4.b provides critical instruction for using obesity class codes:

• Provider Documentation Required: The specific obesity class (1, 2, or 3) must be explicitly documented by the provider. Coders cannot infer the class solely from documented BMI
• Fifth Character Mandatory: All codes under E66.81 require a fifth character to indicate severity (1, 2, or 3)
• BMI Code Assignment: Always use an additional code from Z68.1- through Z68.45 (adults) or Z68.5- (pediatrics) to report the specific BMI when known
• Documentation Standards: The obesity class code reflects the provider's clinical assessment, which may consider factors beyond BMI alone (such as comorbidities, body composition, and metabolic factors)

Relationship to E66.01 (Morbid Obesity)

A key coding question that has emerged involves the relationship between the new E66.813 (Obesity class 3) and the existing E66.01 (Morbid obesity due to excess calories). Here's what you need to know:

Clinical Significance and Use Cases

These obesity class codes serve multiple important functions in healthcare:

• Risk Stratification: Enable more precise risk adjustment in value-based payment models
• Treatment Planning: Support evidence-based treatment algorithms that vary by obesity severity
• Quality Measurement: Facilitate tracking of obesity management interventions and outcomes
• Research and Epidemiology: Allow more granular analysis of obesity trends and treatment effectiveness
• Bariatric Surgery Qualification: Document medical necessity for bariatric procedures based on established criteria

Pediatric Obesity Coding Enhancement

The 2025 updates also enhanced pediatric obesity coding with new codes in the Z68.5- series:

• Z68.51: Body mass index (BMI) pediatric, less than 5th percentile for age
• Z68.52: BMI pediatric, 5th percentile to less than 85th percentile for age
• Z68.53: BMI pediatric, 85th percentile to less than 95th percentile for age
• Z68.54: BMI pediatric, greater than or equal to 95th percentile for age

These codes provide age-appropriate BMI classification for patients under 18 years, using CDC pediatric growth charts rather than adult BMI thresholds.

New Hypoglycemia Level Codes (E16.A-)

Another clinically significant addition to the 2025 ICD-10-CM code set addresses hypoglycemia levels—a critical measurement for diabetes management and continuous glucose monitoring systems.

The New E16.A Series

Code	Description	Blood Glucose Level
E16.A	Hypoglycemia level (parent - not billable)	N/A
E16.A1	Hypoglycemia level 1	54-70 mg/dL (mild)
E16.A2	Hypoglycemia level 2	<54 mg/dL (moderate)
E16.A3	Hypoglycemia level 3	Severe cognitive impairment requiring assistance

Clinical Context and Significance

The hypoglycemia level codes were proposed by the American Diabetes Association and endorsed by the Endocrine Society to standardize hypoglycemia reporting and support better diabetes management. These classifications align with clinical practice guidelines that stratify hypoglycemia by severity:

• Level 1 (Alert): Glucose 54-70 mg/dL - patient can self-treat but should take action
• Level 2 (Clinically Significant): Glucose <54 mg/dL - serious, clinically important hypoglycemia requiring immediate treatment
• Level 3 (Severe): Cognitive impairment requiring external assistance regardless of glucose level

Proper Code Application

The E16.A codes are always used as additional codes in conjunction with the primary diabetes code. They should NEVER be sequenced as the principal or first-listed diagnosis.

Instructional Notes in ICD-10-CM

The 2025 ICD-10-CM manual includes new "Use additional code" notes under multiple diabetes codes, including:

• E10.64- (Type 1 diabetes mellitus with hypoglycemia)
• E11.64- (Type 2 diabetes mellitus with hypoglycemia)
• E13.64- (Other specified diabetes mellitus with hypoglycemia)
• O24.1- (Pre-existing type 1 diabetes in pregnancy)
• O24.3- (Pre-existing type 2 diabetes in pregnancy)

These notes direct coders to "Use additional code for hypoglycemia level, if applicable (E16.A-)"

Impact on Continuous Glucose Monitoring (CGM)

The addition of hypoglycemia level codes directly supports the growing use of continuous glucose monitoring systems. These codes enable:

• Documentation of CGM-detected hypoglycemia events
• Medical necessity support for CGM devices and supplies
• Quality measure reporting for diabetes management
• Research on hypoglycemia patterns and prevention

Lymphoma "In Remission" Codes

The 2025 update includes a substantial expansion of lymphoma codes to include "in remission" status across multiple categories. This change addresses a significant gap in oncology coding, allowing documentation of positive treatment outcomes and disease surveillance phases.

New Remission Status Codes

The following lymphoma categories received new "in remission" codes (indicated by terminal character "A"):

• C81 series: Hodgkin lymphoma - 7 new remission codes (C81.0A through C81.9A)
• C82 series: Follicular lymphoma - 8 new remission codes (C82.0A through C82.9A)
• C83 series: Non-follicular lymphoma - 10 new remission codes
• C84 series: Mature T/NK-cell lymphomas - 10 new remission codes
• C85 series: Other specified and unspecified types of non-Hodgkin lymphoma - 3 new remission codes
• C86 series: Other specified types of T/NK-cell lymphomas - 5 new remission codes
• C88 series: Malignant immunoproliferative diseases - 4 new remission codes

Definition of Remission

In lymphoma coding, "remission" typically refers to complete remission (CR) where:

• No evidence of disease is detectable on physical exam or imaging
• Laboratory values have normalized
• Symptoms related to the lymphoma have resolved
• The patient is in a surveillance phase rather than active treatment

Coders should document remission status based on explicit physician documentation rather than inferring status from treatment completion.

Eating Disorders Expansion (F50)

Category F50 (Eating disorders) received substantial expansion in the 2025 update, with new codes that align with DSM-5 diagnostic criteria and include severity specifiers.

New Eating Disorder Codes

The following eating disorder subcategories now include mild, moderate, severe, extreme, and in remission specifications:

F50.0 - Anorexia Nervosa

• F50.01 - Anorexia nervosa, restricting type
• F50.02 - Anorexia nervosa, binge eating/purging type
• Each with severity levels: mild, moderate, severe, extreme, in remission, unspecified

F50.2 - Bulimia Nervosa

• Expanded to include: mild, moderate, severe, extreme, in remission, unspecified

F50.81 - Binge Eating Disorder

• Expanded to include: mild, moderate, severe, extreme, in remission, unspecified

F50.8 - Other Eating Disorders

• F50.83 - Pica in adults (new code)
• F50.84 - Rumination disorder in adults (new code)
• F50.89 - Other specified eating disorder

Chapter-by-Chapter Highlights

Beyond the major updates covered above, the 2025 ICD-10-CM includes significant changes across multiple chapters. Here's a systematic review of key changes by chapter:

Chapter 1: Certain Infectious and Parasitic Diseases (A00-B99)

• Spelling corrections: "jirovecii" corrected throughout (adding second "i")
• New instructional note: "Use additional code for associated cachexia (E88.A)" added under Tuberculosis codes (A15-A19)
• Ehrlichia species updates: Technical corrections to organism names

Chapter 2: Neoplasms (C00-D49)

This chapter saw the largest number of new codes (47 additions), primarily in lymphoma remission codes described above. Additional changes include:

• Enhanced cancer staging: More specific codes for tumor behavior and morphology
• Rare tumor types: New codes for previously unclassified neoplasms

Chapter 4: Endocrine, Nutritional and Metabolic Diseases (E00-E89)

Major updates include the obesity and hypoglycemia codes discussed above, plus:

• E23.0 Hyperpituitarism: New "use additional code for cachexia" note
• E88.82: New code for obesity due to disruption of MC4R pathway (genetic obesity)
• E88.A: New cachexia code with additional specificity
• Z79.85: Injectable non-insulin diabetic drugs - new status code

Chapter 5: Mental, Behavioral and Neurodevelopmental Disorders (F01-F99)

Beyond eating disorders, this chapter includes:

• Dementia codes expansion: Enhanced specificity for behavioral disturbances and severity
• Schizophrenia updates: Refined terminology and staging
• Substance use disorders: Additional codes for specific substance classifications

Chapter 6: Diseases of the Nervous System (G00-G99)

• G40.84-: New KCNQ2-related epilepsy codes (genetic epilepsy classification)
• G90.81: New code for serotonin syndrome/serotonin toxicity
• G93.45: New code for developmental and epileptic encephalopathy

Chapter 9: Diseases of the Circulatory System (I00-I99)

• I16.1 Hypertensive emergency: New "use additional code" instructions for complications
• I26 Pulmonary embolism: Enhanced detail codes for acute and chronic PE
• I40.0 changes: Viral myocarditis coding updated (now use B33.22 instead)

Chapter 11: Diseases of the Digestive System (K00-K95)

• Fifth and sixth character additions: Greater specificity for inflammatory bowel disease, gastritis, and peptic ulcer disease
• Location-specific codes: Anatomical detail for various digestive conditions

Chapter 13: Diseases of the Musculoskeletal System (M00-M99)

• Synovitis and tenosynovitis expansion: Location-specific codes (right, left, bilateral)
• Osteoarthritis updates: Joint-specific coding enhancements

Chapter 21: Factors Influencing Health Status (Z00-Z99)

• Z15.1: Genetic susceptibility to epilepsy and neurodevelopmental disorders
• Z15.2: Genetic susceptibility to obesity
• Z17 series: Expanded estrogen and hormone receptor status codes
• Z51.A: Encounter for sepsis aftercare
• Z59.71: Insufficient healthcare coverage (social determinant of health)
• Z59.72: Insufficient welfare support (social determinant of health)
• Z68.5- series: Pediatric BMI codes (detailed above)
• Z86.010 expansion: Personal history of colon polyps now specifies polyp types
• Z92.2 expansion: Personal history of drug therapy divided into monoclonal drug therapy and immune checkpoint inhibitor therapy

Official Guidelines Updates

The ICD-10-CM Official Guidelines for Coding and Reporting FY 2025 include important additions and clarifications that affect code assignment across all settings.

New Guideline Section I.C.4.b: Obesity

This entirely new guideline section addresses obesity coding with four critical components:

Other Notable Guideline Clarifications

• Hypoglycemia Level Coding: While not a separate guideline section, instructional notes throughout direct additional code use for E16.A- when applicable
• Social Determinants of Health: Expanded guidance on using Z codes for social factors affecting health
• Present on Admission (POA) Reporting: 429 new POA-exempt codes added, primarily for conditions not "present on admission" by definition

Coding Conventions Remain Stable

The fundamental coding conventions outlined in Section I.A remain unchanged for 2025:

• Code to the highest level of specificity
• Use of placeholder "X" for codes requiring 7 characters
• "And" means "and/or" in the Alphabetic Index
• "With" presumes causal relationship unless documentation indicates otherwise
• Laterality requirements (right, left, bilateral, unspecified)

April 2025 Mid-Year Updates

In addition to the major October 1, 2024 update, the CDC released a mid-year update effective April 1, 2025. While smaller in scope, this update addresses important technical corrections and clarifications.

April 2025 Update Summary

Key April 2025 Changes

Alphabetic Index Updates:

• Decreased blood glucose: Index entry changed from R73.09 to E16.2 (Hypoglycemia, unspecified)
• Hypoglycemia level codes: Moved to additional indentation level under "Decrease(d), blood, glucose"
• Spelling corrections: "jirovecii" corrections throughout

Tabular List Updates:

• Chapter 1: "Use additional code for cachexia" note added to Tuberculosis codes
• Chapter 4: Instructional note additions for hypoglycemia level codes under diabetes categories
• Chapter 9: Important change - viral myocarditis now codes to B33.22 instead of I40.0

Impact on CPC Exam

Understanding the 2025 ICD-10-CM updates is critical for CPC exam success. Here's how these changes specifically impact exam preparation and coding practice:

Exam Content Implications

The CPC exam tests diagnosis coding as approximately 10-15% of exam content. While the AAPC doesn't immediately update exam questions when code sets change, you should be prepared for:

• Scenario-based questions involving newly expanded code categories (obesity, hypoglycemia, eating disorders)
• Guideline application questions testing understanding of the new obesity coding guidelines
• Code selection questions requiring choice between more specific codes (e.g., E66.812 vs. E66.01)
• Instructional note interpretation for "use additional code" requirements

Code Book Navigation

Effective use of your ICD-10-CM code book during the exam requires familiarity with 2025 changes:

• Tab key sections including new code ranges (E16.A-, E66.81-, F50 expansions)
• Guideline quick reference - bookmark Section I.C.4.b (obesity)
• Alphabetic Index updates - be aware of index entry changes
• Convention symbols - understand "New code" indicators in your manual

Common Exam Scenarios Involving 2025 Updates

Practical Coding Examples

Let's walk through several real-world coding scenarios that demonstrate proper application of 2025 updates:

Example 1: Complex Obesity Case

Example 2: Diabetes with Hypoglycemia

Example 3: Lymphoma in Remission

Example 4: Eating Disorder with Severity

Example 5: Social Determinant of Health

Study Tips for CPC Candidates

Mastering the 2025 ICD-10-CM updates requires focused study strategies. Here are proven approaches for CPC exam preparation:

1. Create a "2025 Updates" Study Sheet

Develop a quick-reference sheet with the major 2025 changes. Include:

• Obesity class codes (E66.811-E66.813) with BMI ranges
• Hypoglycemia level codes (E16.A1-E16.A3) with glucose ranges
• Key instructional note changes
• New guideline Section I.C.4.b key points
• Common "use additional code" scenarios

2. Practice with Real Clinical Scenarios

Work through coding exercises that specifically incorporate 2025 updates. Focus on:

• Multi-code scenarios requiring both primary and additional codes
• Guideline application (especially obesity coding rules)
• Choosing between similar codes (E66.813 vs. E66.01)
• Proper sequencing when multiple conditions are present

3. Tab Your Code Book Strategically

Place tabs in your ICD-10-CM manual to quickly locate 2025 updates during timed practice:

• Green tabs: Major new code families (E16.A, E66.81, F50 expansions)
• Yellow tabs: Guideline Section I.C.4.b
• Blue tabs: Z codes (BMI codes, social determinants)
• Red tabs: Frequently tested categories in your practice exams

4. Understand the "Why" Behind Changes

Don't just memorize codes—understand the clinical rationale:

• Obesity classes: Support treatment algorithms and bariatric surgery qualification
• Hypoglycemia levels: Enable CGM documentation and diabetes management tracking
• Lymphoma remission: Distinguish active disease from surveillance
• Eating disorder severity: Align with DSM-5 and support treatment intensity decisions

5. Review Official Resources

Utilize authoritative sources for exam preparation:

• CDC ICD-10-CM Files: Download the official 2025 code files and addendum
• CMS ICD-10-CM Official Guidelines: Review Section I guidelines thoroughly
• AHA Coding Clinic: Read Fourth Quarter 2024 for obesity code guidance
• AAPC Resources: Access AAPC member webinars and articles on 2025 updates

6. Practice Time Management

For the CPC exam, you need to code quickly and accurately:

• 60-second rule: Practice locating codes in under 60 seconds
• Alphabetic Index first: Always start with the Index, then verify in Tabular
• Read instructional notes: Budget time to check for "use additional code" requirements
• Guideline checks: Know when to reference guidelines vs. when you know the rules

7. Join Study Groups

Collaborate with other CPC candidates:

• Quiz each other on 2025 updates
• Share mnemonics and memory aids
• Discuss challenging scenarios
• Review each other's code assignments

8. Take Timed Practice Tests

Simulate exam conditions regularly:

• Include questions specifically on 2025 updates
• Track your speed and accuracy on diagnosis coding questions
• Identify weak areas for focused review
• Practice using only your code books (no notes or references)

Key Takeaways

The 2025 ICD-10-CM updates represent significant progress toward more specific, clinically relevant diagnosis coding. For CPC candidates and medical coders:

• 324 new codes expand specificity across multiple chapters, with major focus on obesity, hypoglycemia, lymphoma, and eating disorders
• New obesity class codes (E66.811-E66.813) require provider documentation and proper BMI code assignment
• Hypoglycemia level codes (E16.A1-E16.A3) are always additional codes used with diabetes codes
• Lymphoma remission codes enable accurate documentation of treatment success and surveillance status
• Official Guidelines Section I.C.4.b provides critical instruction for obesity coding
• April 2025 mid-year update includes important technical corrections and viral myocarditis coding change
• Exam preparation should include focused practice on 2025 updates and guideline application

Stay current with annual ICD-10-CM updates through CDC, CMS, and AAPC resources. Coding accuracy depends on understanding not just the codes themselves, but the clinical context and guidelines that govern their proper application.