ICD-10-CM/PCS Coding Guidelines
Accurate coding using ICD-10-CM and ICD-10-PCS is fundamental to healthcare reimbursement, data quality, and regulatory compliance. The Official Guidelines for Coding and Reporting, published by the Cooperating Parties (AHA, AHIMA, CMS, and NCHS), provide the rules that coders must follow. RHIA candidates must have a strong grasp of these guidelines, coding conventions, and key chapter-specific rules.
ICD-10-CM General Coding Guidelines
The general guidelines apply across all chapters of ICD-10-CM:
- Locating a code: Always begin in the Alphabetic Index, then verify in the Tabular List. Never code directly from the Index alone.
- Level of detail: Assign codes to the highest level of specificity available. If a 4th, 5th, 6th, or 7th character is available, it must be used.
- Placeholder character "X": Used as a placeholder in certain codes to allow for future expansion. The X must be used to hold the position so that subsequent characters are in the correct position.
- 7th character extensions: Required in certain chapters (e.g., injuries, musculoskeletal). Common extensions include A (initial encounter), D (subsequent encounter), and S (sequela).
- Laterality: ICD-10-CM provides codes designating right, left, and bilateral for applicable conditions. When bilateral codes are not available, assign separate codes for right and left.
Key Conventions
| Convention | Meaning |
|---|---|
| Includes notes | Define or clarify the content of a category; the list is not exhaustive |
| Excludes1 | "Not coded here" - the two conditions cannot occur together; the excluded code should never be used with the code above it |
| Excludes2 | "Not included here" - the excluded condition is not part of the condition represented by the code, but a patient may have both conditions simultaneously; both codes may be assigned if documented |
| Code first / Use additional code | Sequencing instructions - "Code first" identifies the underlying condition that should be sequenced first; "Use additional code" identifies a manifestation or associated condition that should be sequenced after the primary code |
| Code also | Two codes may be required, but sequencing depends on the circumstances of the encounter |
| NEC (Not elsewhere classifiable) | The documentation specifies a condition, but the classification does not provide a specific code for it |
| NOS (Not otherwise specified) | The documentation does not provide enough detail for a more specific code; equivalent to "unspecified" |
Selection of Principal Diagnosis
For inpatient coding, the principal diagnosis is defined as "the condition established after study to be chiefly responsible for occasioning the admission of the patient to the hospital for care." Key guidelines include:
- When two or more diagnoses equally meet the definition of principal diagnosis, either may be sequenced first.
- If symptoms are present and a related definitive diagnosis has been established, the definitive diagnosis is coded as principal.
- When a patient is admitted for observation and the observation is negative (no condition found), the signs or symptoms that prompted the observation are coded as principal.
- When a patient is admitted for a procedure that is not performed due to a contraindication, the reason for the planned procedure is sequenced as principal diagnosis.
Chapter-Specific Guidelines Highlights
Selected high-yield chapter rules for exam preparation:
- Chapter 4 - Endocrine (Diabetes): Diabetes codes require type (Type 1, Type 2, secondary), body system affected, and complication. Type 2 is the default when documentation does not specify type. Use as many codes as needed to identify all associated conditions.
- Chapter 9 - Circulatory: Hypertension with heart disease - a causal relationship is assumed unless documentation states otherwise. Assign codes from I11 (hypertensive heart disease) when both conditions are present.
- Chapter 15 - Pregnancy: Codes from Chapter 15 have priority over codes from other chapters for conditions complicating pregnancy. A 7th character identifies the trimester. The final character indicates the fetus for certain codes in multiple gestations.
- Chapter 19 - Injury: Code the most specific injury first. Use 7th character extensions for initial encounter, subsequent encounter, and sequela. External cause codes (Chapter 20) are assigned as additional codes to describe the cause, intent, place, and activity.
- Chapter 21 - Z codes: Z codes represent reasons for encounters other than disease or injury, such as screening, history, and status codes. Some Z codes may only be used as principal/first-listed diagnosis.
ICD-10-PCS Guidelines Overview
ICD-10-PCS uses a fundamentally different structure from ICD-10-CM. Key guidelines include:
- Root operation definition: The root operation is the objective of the procedure. The entire definition of the root operation must be met for a code to be assigned. For example, "Excision" is defined as cutting out or off, without replacement, a portion of a body part. If the entire body part is removed, the root operation is "Resection," not "Excision."
- Components of a procedure: Steps performed to reach the operative site (e.g., laparotomy to reach an abdominal organ) are not coded separately.
- Multiple procedures: Separate procedure codes are assigned when the same root operation is performed on different body parts, different root operations are performed on the same body part, or the same root operation is repeated at different body sites.
- Approach: The approach defines the technique used to reach the operative site: Open, Percutaneous, Percutaneous Endoscopic, Via Natural or Artificial Opening, Via Natural or Artificial Opening Endoscopic, Via Natural or Artificial Opening with Percutaneous Endoscopic Assistance, and External.
Commonly Tested Root Operations
| Root Operation | Definition | Key Distinction |
|---|---|---|
| Excision | Cutting out or off, without replacement, a portion of a body part | Partial removal - biopsy is coded as Excision with the qualifier Diagnostic |
| Resection | Cutting out or off, without replacement, all of a body part | Complete removal of an entire body part |
| Repair | Restoring, to the extent possible, a body part to its normal anatomic structure and function | Used only when the procedure does not meet the definition of another root operation |
| Replacement | Putting in or on biological or synthetic material that physically takes the place and/or function of all or a portion of a body part | The body part may have been taken out previously or may be replaced during the same procedure |
| Bypass | Altering the route of passage of the contents of a tubular body part | Includes rerouting contents to a downstream area or to a similar route and body part |
Exam Preparation Tips
For the RHIA exam, understand the difference between Excludes1 and Excludes2 - this is heavily tested. Know the principal diagnosis definition and be able to apply it in scenario questions. For ICD-10-PCS, focus on distinguishing between similar root operations (Excision vs. Resection, Repair vs. Supplement). Understand the 7th character extensions for injury codes and the trimester designations for obstetric codes.