Standards reference

Coding Standards Reference

A practical reference to the classifications CoderCoach is built around: ICD-10-CM and ICD-10-PCS in the United States, and the WHO’s ICD-11. Code structure, conventions, and worked examples.

ICD-10-CM ICD-10-PCS ICD-11

Diagnosis coding · United States

ICD-10-CM — diagnostic code structure

ICD-10-CM is the U.S. clinical modification of the WHO’s ICD-10, maintained by the CDC’s National Center for Health Statistics (NCHS). Valid codes are 3 to 7 characters long, and a code is only reportable at its highest level of specificity.

Code hierarchy example: E11.22

E11Type 2 diabetes mellitus — category, not reportable on its own
E11.2Type 2 diabetes mellitus with kidney complications — subcategory
E11.22Type 2 diabetes mellitus with diabetic chronic kidney disease ✓ reportable

The code also carries an instruction to use an additional code to identify the stage of chronic kidney disease (N18.-) — exactly the kind of convention coders are expected to apply.

Position	Character	Meaning
1	Letter	Chapter / category range (for example E = endocrine, nutritional and metabolic)
2	Number	Continues the category
3	Letter or number	Completes the three-character category. A decimal point follows this position.
4–6	Letter or number	Etiology, anatomic site, severity, or other clinical detail
7	Letter or number	Extension — required for certain categories, such as the encounter type for injuries

Concepts coders are held to

7th-character extensions

Injury categories require a 7th character for the episode of care: A initial encounter, D subsequent encounter, S sequela (some categories add further values). Example: S72.001A — fracture of unspecified part of neck of right femur, initial encounter for closed fracture.

The placeholder “X”

When a code needs a 7th character but has fewer than six characters, X fills the empty positions. Example: T36.0X1A — poisoning by penicillins, accidental (unintentional), initial encounter.

Excludes1 and Excludes2

Two different notes with two different meanings: Excludes1 means the two conditions generally cannot be reported together; Excludes2 means the conditions can occur together and both may be reported.

Code first / Use additional code

Sequencing instructions that tell the coder which code must come first (for example, an underlying condition before a manifestation) and which additional codes complete the picture.

NEC and NOS

“Not elsewhere classifiable” and “not otherwise specified” are not interchangeable — choosing between them depends on whether more specific documentation exists.

Laterality

Many codes are specific to the right, left, or bilateral side. Missing or unspecified laterality is one of the most common reasons a code is less specific than it should be.

Official Guidelines for Coding and Reporting

The ICD-10-CM Official Guidelines for Coding and Reporting are published annually by CMS and NCHS, with a fiscal-year effective date of October 1. They are organized in four sections:

Section I — Conventions, general coding guidelines, and chapter-specific guidelines
Section II — Selection of principal diagnosis
Section III — Reporting additional diagnoses
Section IV — Diagnostic coding and reporting guidelines for outpatient services

Procedure coding · United States inpatient

ICD-10-PCS — procedure code structure

ICD-10-PCS is the U.S. procedure coding system for inpatient hospital settings, maintained by CMS. Every code is exactly seven characters, with no decimal point. Each character is an axis, and codes are built by selecting a value for each axis from the classification’s tables rather than looked up as a single entry.

Worked example: 0FT44ZZ — laparoscopic cholecystectomy

Resection of gallbladder, percutaneous endoscopic approach

1	2	3	4	5	6	7
0	F	T	4	4	Z	Z
Section: Medical and Surgical	Body system: Hepatobiliary system and pancreas	Root operation: Resection	Body part: Gallbladder	Approach: Percutaneous endoscopic	Device: No device	Qualifier: No qualifier

17 sections

The first character is the section. Section 0 (Medical and Surgical) is the largest; others include Obstetrics, Placement, Administration, Imaging, and New Technology. The meaning of characters 2–7 depends on the section.

Character values

Each position uses the digits 0–9 and the letters A–H, J–N, and P–Z. The letters I and O are never used, to avoid confusion with 1 and 0.

31 root operations

In the Medical and Surgical section, the third character is a root operation defined by its objective — for example Excision (a portion of a body part), Resection (all of a body part), Bypass, and Replacement. Choosing correctly between them is the core skill.

Approach values

The fifth character records how the procedural site was reached: 0 open, 3 percutaneous, 4 percutaneous endoscopic, 7 via natural or artificial opening, 8 via natural or artificial opening endoscopic, F via natural or artificial opening with percutaneous endoscopic assistance, X external.

International classification · WHO

ICD-11 — a new structure for a new generation of health data

ICD-11 is the World Health Organization’s eleventh revision of the International Classification of Diseases. It came into effect on 1 January 2022 and is being adopted by health systems at different paces around the world. In the United States, ICD-10-CM remains the required diagnosis code set.

Alphanumeric stem codes

Codes are alphanumeric and built on a four-character stem. Example: 5A11 — type 2 diabetes mellitus.

Foundation and MMS

The Foundation Component is the full underlying knowledge base. The Mortality and Morbidity Statistics (MMS) linearization is the code set used for reporting, organized into 26 chapters.

Extension codes

Extension codes, which begin with X, add detail such as severity, laterality, or causal agent to a stem code rather than multiplying the number of stem codes.

Postcoordination and clusters

A stem code and its extensions are joined with &, and stem codes that together describe one condition are clustered with /. Coders need to know when each is required or optional.

Coding in Canada? ICD-10-CA and CCI are a different system.

Canada uses ICD-10-CA for diagnoses and the Canadian Classification of Health Interventions (CCI) for procedures — not ICD-10-CM or ICD-10-PCS. For example, ICD-10-CM’s E11.22 does not exist in ICD-10-CA, where the equivalent is E11.2. The CoderCoach Canadian Edition is built on the Canadian standards, licensed from CIHI.

Canadian Standards Reference

Standards attribution

ICD-10-CM is maintained by the U.S. National Center for Health Statistics (NCHS) and ICD-10-PCS by the Centers for Medicare & Medicaid Services (CMS); both are in the public domain in the United States. ICD-10 and ICD-11 are © World Health Organization. This page is an educational summary and not a substitute for the official publications — always verify against the official standards for your jurisdiction and fiscal year. CoderCoach is not affiliated with, sponsored by, or endorsed by NCHS, CMS, or the WHO.

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