How to Use the ICD-10-CM Alphabetic Index and Tabular List: A Beginner’s Guide

Introduction

ICD-10-CM (International Classification of Diseases, Tenth Revision, Clinical Modification) is used to classify and code diagnoses in healthcare settings in the United States. Medical coders use ICD-10-CM codes to represent documented diagnoses accurately for medical billing, claims processing, reporting, and statistical purposes.
For beginners, one of the most important skills in ICD-10-CM coding is learning how to use the Alphabetic Index and the Tabular List together. The Alphabetic Index helps you locate a potential code based on a documented medical term, while the Tabular List allows you to verify the code and review the instructions that apply to it.
Simply finding a code in the Index is not enough. Medical coders must verify the code in the Tabular List, follow the official coding guidelines, and ensure that the documentation supports the code selected.
In this guide, you will learn how to navigate both tools, understand their differences, and follow a systematic process when looking up ICD-10-CM diagnosis codes.

What You Will Learn

By the end of this guide, you will be able to:

• Explain the difference between the Alphabetic Index and the Tabular List.
• Locate a documented diagnosis in the Alphabetic Index.
• Verify a potential code in the Tabular List.
• Recognize important coding instructions and code-specific requirements.
• Avoid common mistakes when looking up ICD-10-CM codes.
• Use official resources to check the applicable ICD-10-CM code set and guidelines.

1. What Is the ICD-10-CM Alphabetic Index?

The Alphabetic Index is the starting point for locating ICD-10-CM diagnosis codes. It organizes medical terms alphabetically and helps coders identify a potential code based on the provider’s documented diagnosis.
The Index contains several types of entries, including:

• Main terms: The primary words used to locate a diagnosis.
• Subterms: Indented entries that provide additional details about the condition.
• See references: Instructions directing the coder to another term.
• See also references: Suggestions to review another related term when appropriate.

How to Use the Alphabetic Index

Follow these steps when searching for a diagnosis:

1. Identify the documented diagnosis. Read the medical record and identify the condition documented by the healthcare provider.
2. Locate the main term. Search for the key medical term in the Alphabetic Index.
3. Review the subterms. Check for details such as the anatomical site, type of condition, or other documented characteristics.
4. Follow cross-references. If the Index directs you to another term, follow that instruction.
5. Identify the potential code. Note the code or code reference listed in the Index.
6. Verify the code in the Tabular List. Never finalize code assignment using the Alphabetic Index alone.

Practical Example

Suppose a provider documents acute bronchitis in a patient’s medical record.
A beginner should not guess the code based only on familiarity with the diagnosis. Instead:

1. Locate the main term Bronchitis in the Alphabetic Index.
2. Review the applicable subterms, including the documented type or acuity.
3. Follow any applicable instructions in the Index.
4. Locate the resulting code in the Tabular List.
5. Confirm that the code description and all applicable instructions support the documented diagnosis.

Important: This is a demonstration of the lookup process, not a substitute for checking the current official ICD-10-CM code set.

2. What Is the ICD-10-CM Tabular List?

The Tabular List is the organized listing of ICD-10-CM diagnosis codes, arranged by category and code structure. It provides the official code descriptions and important instructions that medical coders must review before assigning a diagnosis code.
The Tabular List is essential because a code found in the Alphabetic Index may require additional verification before it can be reported.

Important Features of the Tabular List

1. Code descriptions
Each code has a description that identifies the condition or diagnosis represented by that code. Confirm that the description matches the provider’s documentation.
2. Inclusion terms
These terms identify diagnoses or conditions included within a particular code or category. They help clarify the scope of the code.
3. Excludes1 notes
An Excludes1 note generally indicates that the excluded condition should not be coded together with the code above the note. However, official guidelines describe limited circumstances in which both conditions may be reported when they are unrelated. Review the applicable guidelines before assigning codes.
4. Excludes2 notes
An Excludes2 note means that the excluded condition is not included in the code above the note. Both conditions may be reported together when the documentation supports them and no other coding instruction prevents it.
5. Code first notes
A Code first instruction identifies a sequencing requirement. When applicable, the underlying condition must be coded before the condition associated with the instruction.
6. Use additional code notes
A Use additional code instruction indicates that another code may be required to provide additional information, such as an associated condition or manifestation. Follow the applicable sequencing instructions and official guidelines.
7. Additional code requirements
Some codes require a specified number of characters, a placeholder, or a seventh character. Always review the complete code structure and applicable notes.

Practical Example

Imagine that you have located a potential diagnosis code in the Alphabetic Index.
Before assigning it, open the corresponding entry in the Tabular List and check:

• Does the code description match the documented diagnosis?
• Is the code complete and valid for the applicable fiscal year?
• Are there inclusion terms or Excludes notes?
• Is a Code first or Use additional code instruction present?
• Are additional characters or a seventh character required?
• Are there other applicable chapter-specific or official guideline requirements?

Key takeaway: The Alphabetic Index helps you locate a potential code; the Tabular List helps you verify it and apply the relevant coding instructions. Both must be used together.

3. Step-by-Step Process for Finding an ICD-10-CM Code

Medical coders should follow a systematic process when assigning ICD-10-CM diagnosis codes. The following workflow is useful for beginners, medical coding students, and CPC exam aspirants.

Step 1: Review the Medical Documentation

Read the provider’s documentation carefully. Identify the diagnosis, relevant details, and any documented relationships between conditions. Do not assign a diagnosis based only on symptoms or assumptions when the documentation does not support it.

Step 2: Identify the Main Term

Determine the key medical term that represents the documented condition. This term will usually guide your search in the Alphabetic Index.

Step 3: Search the Alphabetic Index

Locate the main term and review the applicable subterms. Pay attention to documented details such as acuity, anatomical site, type of condition, and other relevant information.
Follow any applicable cross-references and record the potential code.

Step 4: Verify the Code in the Tabular List

Locate the potential code in the Tabular List. Confirm that the code description matches the documentation and review all applicable notes and instructions.

Step 5: Check Code Specificity

Determine whether the code requires additional characters, a placeholder, a seventh character, or other code-specific details. Check whether the code is complete and valid for the applicable fiscal year.

Step 6: Review Official Coding Guidelines

Consult the applicable ICD-10-CM Official Guidelines for Coding and Reporting. Consider any relevant chapter-specific rules, sequencing instructions, and documentation requirements.

Step 7: Assign the Code Only When Supported

Ensure that the selected code accurately represents the documented diagnosis and satisfies applicable coding requirements. If the documentation is unclear or conflicting, follow your organization’s procedures for clarification rather than guessing.

Quick Reference Checklist

Before finalizing a diagnosis code, ask yourself:

• Have I reviewed the provider’s documentation?
• Have I searched the Alphabetic Index?
• Have I verified the code in the Tabular List?
• Have I reviewed all applicable instructional notes?
• Have I confirmed the required characters and code validity?
• Have I followed the applicable official coding guidelines?

Following this workflow helps reduce coding errors and builds consistent habits for professional medical coding.

4. Worked Example: Finding an ICD-10-CM Diagnosis Code

Let’s walk through a practical example to understand how the Alphabetic Index and Tabular List work together.

Clinical Scenario

A healthcare provider documents acute bronchitis in a patient’s medical record. The coder needs to identify the appropriate ICD-10-CM diagnosis code.

Step 1: Review the Documentation

Identify the diagnosis documented by the provider: acute bronchitis.
Do not assume additional details that are not documented.

Step 2: Search the Alphabetic Index

Locate the main term Bronchitis and review the applicable subterms. Follow the Index instructions to identify the potential code for acute bronchitis.

Step 3: Verify the Code in the Tabular List

For this example, the code commonly associated with acute bronchitis is J20.9 — Acute bronchitis, unspecified.
Open the official Tabular List for the applicable fiscal year and confirm the code description and any applicable instructions before assigning it.

Step 4: Confirm the Final Code

Check that the documentation supports the diagnosis and that no additional information changes the code selection.
If the provider documents a more specific cause or type of bronchitis, review the Index and Tabular List again to determine whether a more specific code applies.

What Does This Example Teach Us?

This example demonstrates three important principles:

• The provider’s documentation guides code selection.
• The Alphabetic Index helps identify a potential code.
• The Tabular List must be reviewed before final code assignment.

Remember: This example is for educational purposes. Always verify the current fiscal-year code set and applicable official guidelines before using a code in actual coding work.

5. Common Mistakes to Avoid When Using ICD-10-CM

Learning to use the Alphabetic Index and Tabular List correctly takes practice. Beginners can avoid many coding errors by following a consistent lookup process.

1. Assigning a Code Directly From the Alphabetic Index

Mistake: Selecting a code from the Index without checking the Tabular List.
How to avoid it: Always verify the potential code in the Tabular List and review the applicable instructional notes before assigning it.

2. Ignoring Subterms

Mistake: Looking only at the main term without reviewing the indented subterms.
How to avoid it: Review the relevant subterms carefully. They may distinguish between different types, locations, or stages of a condition.

3. Overlooking Excludes Notes

Mistake: Assigning codes without checking applicable Excludes1 or Excludes2 notes.
How to avoid it: Read the notes at the relevant code and category levels, and follow the official coding guidelines when determining whether both conditions may be reported.

4. Ignoring Code Specificity

Mistake: Reporting an incomplete code or overlooking a required character.
How to avoid it: Check the full code structure, placeholder requirements, seventh-character requirements, and applicable fiscal-year validity.

5. Assuming a Diagnosis That Is Not Documented

Mistake: Inferring a diagnosis from symptoms, medications, or other information without sufficient documentation.
How to avoid it: Follow the applicable coding guidelines and organizational procedures. Seek clarification when required rather than making unsupported assumptions.

6. Using an Outdated Code Set

Mistake: Using a code or guideline from an earlier fiscal year without checking whether it remains applicable.
How to avoid it: Verify codes using the official ICD-10-CM files and guidelines for the relevant fiscal year.

7. Missing Additional Coding Instructions

Mistake: Overlooking instructions such as Code first, Use additional code, or other applicable notes.
How to avoid it: Review all relevant instructions and apply the required sequencing and additional-code rules.

Key Takeaway

Accurate ICD-10-CM coding requires more than finding a matching diagnosis term. Review the documentation, search the Alphabetic Index, verify the code in the Tabular List, and apply the relevant official guidelines.

6. Official ICD-10-CM Learning Resources

Medical coding students should develop the habit of consulting official resources rather than relying exclusively on search engines, third-party websites, or memorized codes.
The following resources are useful for learning and verifying ICD-10-CM information.

1. CDC ICD-10-CM Browser Tool

The Centers for Disease Control and Prevention’s National Center for Health Statistics provides an official browser tool that allows users to search the Alphabetic Index and Tabular List and review code-specific information.
Visit: https://icd10cmtool.cdc.gov/

2. CMS ICD-10 Code Files

The Centers for Medicare & Medicaid Services provides official ICD-10-CM code files, Tabular List and Index files, code descriptions, and related updates.
Visit: https://www.cms.gov/medicare/coding-billing/icd-10-codes

3. ICD-10-CM Official Guidelines for Coding and Reporting

The official guidelines explain general coding principles, chapter-specific requirements, and other rules that support accurate code assignment and sequencing.
For encounters on or after October 1, 2026, consult the applicable FY 2027 guidelines and code set.
Official guidelines: https://www.cms.gov/files/document/fy-2027-icd-10-cm-coding-guidelines.pdf
Study tip: Always check the fiscal year applicable to the date of service. ICD-10-CM code sets and guidelines are updated periodically, so an older reference may not reflect current requirements.

7. Frequently Asked Questions

Can I assign an ICD-10-CM code directly from the Alphabetic Index?

No. The Alphabetic Index is the starting point for locating a potential code. Verify the code in the Tabular List and follow all applicable coding instructions before assigning it.

What is the main difference between the Alphabetic Index and the Tabular List?

The Alphabetic Index organizes terms alphabetically and helps identify potential codes. The Tabular List organizes codes and provides their descriptions and applicable instructions.

Why are Excludes1 and Excludes2 notes important?

These notes explain coding relationships between conditions and can affect whether two codes may be reported together. Their application depends on the relevant instructions and official guidelines.

Should I use the same ICD-10-CM code set every year?

Not necessarily. Code sets and guidelines can change. Always verify the code set applicable to the date of service and the fiscal year.

Is memorizing ICD-10-CM codes enough to become a good medical coder?

Memorization can help, but it is not enough. A skilled coder knows how to interpret documentation, navigate the Index, verify codes in the Tabular List, and apply official guidelines.

Conclusion

Learning to use the ICD-10-CM Alphabetic Index and Tabular List is a fundamental skill for every medical coding student. The Index helps you locate a potential code, while the Tabular List allows you to verify the code and review important coding instructions.
By following a systematic lookup process, reviewing documentation carefully, avoiding common mistakes, and consulting official resources, beginners can build a strong foundation in ICD-10-CM coding.
At Mecopedia, our goal is to support medical coding students and CPC exam aspirants with educational guides, practice questions, and learning resources that help them develop their coding knowledge.
Keep practising with documented scenarios, verify your code selections, and make consulting official coding references part of your daily study routine.
Disclaimer: This article is intended for educational purposes only. It does not replace official ICD-10-CM code files, coding guidelines, professional judgment, or employer-specific coding policies. Always verify code assignments using the applicable official resources.