How to Use the ICD-10-CM Alphabetic Index Like a Pro

The ICD-10-CM Alphabetic Index is the starting point for every diagnosis code lookup. The coding guidelines are explicit about this: you must begin your code search in the Alphabetic Index and then verify the code in the Tabular List. Skipping the Index and going directly to the Tabular List is a coding error that leads to missed codes, incorrect specificity, and wrong answers on the CPC exam.

Despite its importance, many new coders underuse the Index or misunderstand how it is organized. The Index is not a simple alphabetical list of diseases — it is a structured hierarchy of main terms, subterms, and cross-references that guides you to the most specific code available. This guide covers everything you need to know about using the Index effectively, from basic navigation to the advanced lookup strategies that save time on exam day. For a broader overview of ICD-10-CM before diving into index navigation, see What Is ICD-10-CM.

Structure of the Alphabetic Index

The ICD-10-CM Alphabetic Index is organized into three separate sections, each serving a distinct purpose.

The Index to Diseases and Injuries

This is the main section and the one you will use most frequently. It contains an alphabetical listing of main terms for diseases, conditions, injuries, signs, symptoms, and other reasons for encounters. Each main term has indented subterms that add specificity — anatomic site, type, etiology, severity, or other clinical detail.

The Table of Neoplasms

This is a specialized table within the Index that lists anatomical sites alphabetically in the left column and provides six code columns across the top: Malignant Primary, Malignant Secondary, Ca in situ, Benign, Uncertain Behavior, and Unspecified Behavior. When coding a neoplasm, you look up the anatomical site in this table and select the code from the appropriate behavior column. For complete neoplasm coding guidance, see Neoplasm Coding in ICD-10-CM.

The Table of Drugs and Chemicals

This table lists substances alphabetically and provides code columns for different intent categories: Accidental (Unintentional), Intentional Self-Harm, Assault, Undetermined, and Adverse Effect. When a patient has a condition caused by a drug or chemical, you use this table to find the appropriate external cause code. The Table of Drugs and Chemicals is critical for injury and poisoning coding — see Injury Coding and 7th Characters for related rules.

The External Cause of Injuries Index

This fourth section indexes external causes of morbidity (V00–Y99 codes) by type of event — such as falls, transport accidents, assaults, and complications of medical care. While less frequently tested than the main Index, CPC candidates should know it exists and when to use it.

Main Terms and Subterms

Understanding how main terms and subterms work is the foundation of Index navigation.

What Qualifies as a Main Term

Main terms are printed in boldface type and are flush left in the Index. They are typically one of the following:

• Disease or condition names — Diabetes, Fracture, Pneumonia, Hypertension
• Nouns describing the condition — Abscess, Obstruction, Stenosis, Insufficiency
• Adjectives in some cases — Abnormal, Enlarged, Elevated

Main terms are never anatomical sites by themselves. You do not look up “knee” or “lung” as a main term for a disease. Instead, you look up the condition affecting that site — “Fracture” for a broken knee, “Pneumonia” for a lung infection. The anatomical site appears as a subterm under the condition.

How Subterms Work

Subterms are indented under the main term and provide additional specificity. They are organized hierarchically — each level of indentation narrows the description further. Subterms may indicate:

• Anatomical site — Fracture → femur → neck → displaced
• Type or cause — Diabetes → type 1 → with → kidney complications
• Acuity — Bronchitis → acute → with obstruction
• Associated conditions — Hypertension → with → heart disease

When multiple levels of subterms exist, you must read from the main term down through each indentation level to build the complete code reference. Skipping a subterm level can lead you to a less specific or incorrect code.

The Default Code

Many main terms have a code listed immediately after them, before any subterms. This is the default code — the code assigned when no additional subterm information applies or when the documentation does not provide further specificity. For example, “Appendicitis” has a default code, but if the documentation specifies “acute” appendicitis, you follow the subterm “acute” to a more specific code.

Cross-References in the Index

The Index uses three types of cross-references that direct you to look elsewhere for the correct code.

“See” References

A “see” reference is mandatory. It tells you that the term you looked up is not indexed at that location and directs you to the correct main term. You must follow the reference — there is no code at the original location.

Example: If you look up “Flu,” you may see a reference that says “see Influenza.” You must go to “Influenza” to find the codes.

“See Also” References

A “see also” reference is advisory. It tells you that additional relevant entries exist under another main term. You should check the referenced term if the subterms under your current main term do not fully describe the documented condition.

Example: Under “Inflammation,” you might see “see also” references to more specific condition entries. If you find what you need under “Inflammation,” you can use it. If not, follow the “see also” reference.

“See Category” References

A “see category” reference directs you to a specific category in the Tabular List rather than to another Index entry. This is common for conditions where the Tabular List organization provides better guidance than the Index hierarchy.

Step-by-Step Index Lookup Process

The correct process for using the Alphabetic Index follows a consistent sequence that the ICD-10-CM coding guidelines require.

Step 1 — Identify the main term. Read the diagnostic statement and determine the condition or reason for the encounter. The main term is usually the noun that names the disease, injury, or condition — not the anatomical site.

Step 2 — Locate the main term in the Index. Find the boldface entry in the alphabetical listing. If the exact term is not found, check for synonyms or follow any “see” references.

Step 3 — Read the subterms. Scan the indented subterms under the main term for modifiers that match the documentation — site, type, cause, acuity, laterality, or associated conditions. Follow the indentation levels down to the most specific match.

Step 4 — Note the code. Record the code (or code range) listed next to the most specific subterm that matches the documentation.

Step 5 — Verify in the Tabular List. Go to the Tabular List and locate the code. Read all instructional notes, Includes notes, Excludes notes, Code first/Use additional code instructions, and verify the code is valid at the character level shown. Check for required additional characters (4th, 5th, 6th, 7th).

Step 6 — Assign the code. Only after Tabular List verification is the code assignment complete.

Never code directly from the Index. The Index does not contain all the instructional notes, inclusion terms, or character requirements that the Tabular List provides. Coding from the Index alone will result in errors.

Common Index Navigation Challenges

Eponyms

An eponym is a condition named after a person — such as Parkinson’s disease, Cushing’s syndrome, or Colles’ fracture. Eponyms are listed alphabetically in the Index by the person’s name. If you cannot find a condition by its clinical name, check the eponym. Conversely, if you look up the eponym and see a “see” reference, follow it to the clinical term.

Conditions with Multiple Main Term Options

Some conditions can logically be looked up under more than one main term. For example, “acute appendicitis” could be searched under “Appendicitis” (the condition) or under “Acute” (the descriptor). The Index typically lists both pathways, but the condition name is usually the more reliable entry point because it has the most complete subterm hierarchy.

Connecting Words — “with,” “due to,” “in,” “associated with”

These connecting words appear as subterms and indicate relationships between conditions. The word “with” has special significance in ICD-10-CM — it implies an assumed causal relationship for certain conditions (especially diabetes and hypertension) without requiring the physician to explicitly state causality. See ICD-10-CM Sequencing Rules for more on how these relationships affect code order.

Combination Codes in the Index

The Index often points directly to combination codes — single codes that capture two or more clinical concepts. When a subterm leads you to a combination code, verify in the Tabular List that the combination code fully describes all documented elements before assigning it.

Using the Table of Neoplasms

The Table of Neoplasms requires a specific approach:

1. Determine the behavior of the neoplasm from the documentation — malignant (primary or secondary/metastatic), carcinoma in situ, benign, uncertain behavior, or unspecified.
2. Look up the anatomical site in the left column of the table.
3. Select the code from the column that matches the documented behavior.
4. Verify the code in the Tabular List — check for required additional characters and instructional notes.

A common exam mistake is selecting from the wrong behavior column — particularly confusing malignant primary with malignant secondary, or using unspecified when the documentation actually states the behavior.

Using the Table of Drugs and Chemicals

The Table of Drugs and Chemicals is used whenever a condition results from a substance — whether a medication, chemical, biological agent, or other substance. The lookup process: find the substance name in the alphabetical listing (left column); determine the intent from the documentation — accidental, intentional self-harm, assault, undetermined, or adverse effect (correct use of a properly prescribed medication); select the code from the appropriate intent column; verify in the Tabular List and add required 7th character extensions (A for initial encounter, D for subsequent, S for sequela).

The distinction between poisoning and adverse effect is heavily tested. An adverse effect occurs when a medication is taken correctly as prescribed but causes an unintended reaction. A poisoning occurs when a substance is taken incorrectly — wrong dose, wrong substance, wrong person, or with intent to harm.

CPC Exam Strategies for Index Use

The CPC exam is open-book, and efficient Index navigation directly affects your time management. Here are strategies that save minutes on exam day:

Know your main term patterns. Most CPC exam questions test conditions that fall into predictable main term categories — disease names, procedure-related complications, signs and symptoms, and Z-code reasons for encounters. Practice identifying main terms from clinical scenarios before exam day.

Use guide words. The top of each Index page shows guide words (like a dictionary) indicating the alphabetical range on that page. Use these to navigate quickly instead of scanning every entry.

Tab your manual. Place tabs at the start of each letter section in the Index, at the Table of Neoplasms, and at the Table of Drugs and Chemicals. Also tab the beginning of the Tabular List. These tabs eliminate page-flipping time.

Do not linger. If you cannot find a main term within 30 seconds, try a synonym, check for an eponym, or approach the condition from a different angle (the broader category instead of the specific subtype). The Index has multiple pathways to most codes.

For more exam preparation strategies, see the CPC Exam Study Guide and the CPC Exam Cheat Sheet.

Frequently Asked Questions