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Healthcare IT Glossary

What is ICD-10?
International Classification of Diseases

Every diagnosis documented in a clinical encounter eventually becomes a code. That code determines what the payer reimburses, what the quality report measures, and what the population health dashboard displays. ICD-10 is the code set behind nearly all of it — a massive classification system that assigns a unique alphanumeric code to every disease, injury, and cause of death recognized in modern medicine.

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Definition of ICD-10How ICD-10 Works in HealthcareKey ICD-10 Standards and SpecificationsImplementation ConsiderationsHow Taction Helps with ICD-10

Definition of ICD-10

ICD-10, which stands for International Classification of Diseases, 10th Revision, is a medical classification system maintained by the World Health Organization (WHO) that provides codes for diseases, signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. It serves as the global standard for diagnostic classification.

In the United States, healthcare uses two ICD-10 derivatives:

ICD-10-CM (Clinical Modification) — Maintained by the CDC’s National Center for Health Statistics. ICD-10-CM is used for diagnosis coding in all clinical settings — hospitals, physician offices, outpatient clinics, and emergency departments. It contains approximately 72,000 codes and is significantly more granular than its predecessor, ICD-9-CM, which had roughly 14,000.

ICD-10-PCS (Procedure Coding System) — Maintained by CMS. ICD-10-PCS is used exclusively for inpatient hospital procedure coding. It contains approximately 87,000 codes and uses a seven-character alphanumeric structure designed for precision — specifying not just what procedure was performed, but the approach, body part, device used, and qualifier.

ICD-10-CM is required under HIPAA for all covered entities conducting electronic transactions. Every diagnosis on an EDI 837 claim must use ICD-10-CM codes. Every EHR system must support ICD-10-CM for clinical documentation and billing.

In simple terms: ICD-10 is the universal language for diagnoses — the code set that translates a clinical finding into something every system in healthcare can understand, process, and act on.

How ICD-10 Works in Healthcare

ICD-10 codes flow through nearly every administrative and clinical system in a healthcare organization. They’re generated during clinical documentation and consumed by billing, analytics, quality reporting, and public health surveillance systems.

Here’s the lifecycle:

Clinical documentation
A provider sees a patient, evaluates symptoms, and reaches a clinical assessment. The diagnosis is documented in the EHR — either as free text that’s later coded, or directly as an ICD-10-CM code selected from the EHR’s coding module. Modern EHRs provide real-time code search, auto-suggestion based on documentation context, and AI-assisted coding that recommends codes from the clinical narrative.
Coding and compliance
In many organizations, professional coders review clinical documentation to assign or validate ICD-10 codes before claims are submitted. This step is critical for revenue integrity — incorrect codes lead to claim denials, underpayment, or compliance risk. Coding accuracy is measured by specificity (coding to the highest level of detail supported by documentation) and accuracy (matching the code to what was clinically documented).
Claims submission
ICD-10-CM codes are embedded in EDI 837 transactions as diagnosis codes linked to specific service lines. Payers adjudicate claims based on these codes — determining medical necessity, applying coverage rules, and calculating reimbursement. A missing or incorrect ICD-10 code is one of the most common reasons for claim denial.
Reimbursement and DRG assignment
For inpatient hospital claims, ICD-10-CM and ICD-10-PCS codes feed into the DRG (Diagnosis-Related Group) grouper algorithm, which assigns the encounter to a payment category. The DRG determines how much Medicare or the commercial payer reimburses the hospital. Coding precision directly impacts revenue cycle performance — a single missing complication or comorbidity code can shift a claim to a lower-paying DRG.
Quality reporting and analytics
ICD-10 codes are the foundation of clinical quality measures reported to CMS programs like MIPS, Hospital Value-Based Purchasing, and Accountable Care Organizations. Population health platforms aggregate ICD-10-coded data to identify disease prevalence, track chronic condition management, and stratify patient risk.
Public health surveillance
State and federal public health agencies use ICD-10 data to monitor disease trends, track outbreaks, measure mortality causes, and allocate resources. The granularity of ICD-10 — distinguishing, for example, between initial encounter, subsequent encounter, and sequela for every injury — provides a level of epidemiological precision that ICD-9 couldn’t deliver.

Key ICD-10 Standards and Specifications

The seventh character often indicates encounter type: A (initial), D (subsequent), S (sequela). This level of specificity is what makes ICD-10 both powerful for analytics and demanding for coders.

Legacy
ICD-10-CM Code Structure
ICD-10-CM codes are three to seven characters long. The first character is always a letter (A–Z, excluding U). Characters 2–3 are numeric. Characters 4–7 provide increasing specificity — body site, laterality, encounter type, and other clinical details. For example:
Modern
Annual Code Updates
CMS releases ICD-10-CM and ICD-10-PCS code updates annually, effective October 1 each fiscal year. New codes are added, existing codes are revised, and some codes are deleted. EHR systems, billing platforms, and clinical data systems tools must update their code tables annually to stay current.
Legacy
ICD-10 and SNOMED CT
SNOMED CT and ICD-10 serve different purposes but overlap significantly. SNOMED CT is a clinical terminology — it captures what the clinician observed and assessed with high granularity. ICD-10 is a classification system — it groups clinical findings into standardized categories for billing, reporting, and statistics. Many EHR systems map between the two: clinicians document using SNOMED CT terms, and the system crosswalks to ICD-10 codes for billing.
Modern
ICD-11
The WHO released ICD-11 in 2019, and it took effect internationally in January 2022. However, the United States has not adopted ICD-11 and continues to use ICD-10-CM and ICD-10-PCS. There is currently no announced timeline for U.S. transition to ICD-11 — organizations should continue investing in ICD-10 capabilities.
S72Fracture of femur
S72.0Fracture of head and neck of femur
S72.001AFracture of unspecified part of neck of right femur, initial encounter
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Implementation Considerations

ICD-10 touches almost every system in a healthcare organization. Implementation and ongoing maintenance require coordination across clinical, billing, IT, and compliance teams.

EHR coding modules need regular updates
Every EHR and practice management system must load the latest ICD-10-CM code tables before each October 1 effective date. Failing to update means providers can’t code new diagnoses, and claims will be rejected for invalid codes. Build this into your annual IT maintenance calendar.
AI and NLP are transforming coding workflows
Generative AI and natural language processing are increasingly used to auto-suggest ICD-10 codes from clinical documentation — reducing coder workload and improving coding specificity. However, AI-assisted coding requires validation pipelines and human oversight to maintain accuracy and compliance.
Coding specificity drives revenue
Undercoding — assigning less specific codes than the documentation supports — directly reduces reimbursement. For inpatient claims, missing CC (Complication/Comorbidity) or MCC (Major Complication/Comorbidity) codes can drop a DRG by one or more tiers. Clinical documentation improvement (CDI) programs work alongside coding teams to ensure documentation supports the highest justified specificity.
Denial management links back to ICD-10
A significant percentage of claim denials relate to diagnosis coding — invalid codes, codes not supported by documentation, missing laterality, or diagnosis/procedure mismatches. Your revenue cycle workflow should include denial analytics that categorize and track ICD-10-related rejections.
Analytics and
big data platforms depend on code quality. ICD-10-coded data feeds population health dashboards, risk adjustment models, value-based care calculations, and research datasets. If coding quality is inconsistent — codes are too general, inaccurate, or missing — downstream analytics produce unreliable results. Data governance for ICD-10 is as important as the coding itself.
Testing after code updates
Every annual ICD-10 update requires regression testing across EHR, billing, analytics, and reporting systems. New codes must be searchable. Deleted codes must be flagged. Crosswalks between SNOMED CT and ICD-10 must be updated. Build automated testing into your update workflow.

How Taction Helps with ICD-10

At Taction, our team builds and integrates systems that handle ICD-10 coding, billing, and analytics — from EHR coding modules to enterprise revenue cycle platforms and population health dashboards.

What we do:

Whether you’re building coding capabilities into a new product, optimizing your revenue cycle around coding accuracy, or standing up analytics that depend on clean ICD-10 data, our healthcare technology team delivers.

EHR coding module development
We build and customize ICD-10-CM and ICD-10-PCS coding modules within EHR and EMR platforms — including code search, auto-suggestion, code validation, and annual update automation.
AI-powered coding assistance
We develop AI clinical tools that analyze clinical documentation and recommend ICD-10 codes, improving coding speed, specificity, and consistency.
Revenue cycle integration
We integrate ICD-10 coding workflows with claims submission, denial management, and payment posting systems — connecting clinical documentation to billing automation end-to-end.
Analytics and reporting
We build population health and quality reporting platforms that aggregate ICD-10-coded data for CMS quality programs, risk adjustment, and organizational performance dashboards.
Code update management
We automate the annual ICD-10 code table refresh across EHR, billing, and analytics systems — including regression testing, crosswalk updates, and stakeholder notification.

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