Introducing ICD-10

2015 - 4 August – Post-Intensive Care Syndrome
David L. Carpenter, MPAS, PA-C
In this article, an expert outlines the basic concepts of transitioning to ICD-10 coding.


As of October 1, 2015, all codes for medical diagnosis and inpatient procedures for patients covered by the Health Insurance Portability and Accountability Act were required to transition from International Classification of Diseases (ICD)-9 codes to ICD-10. This change resulted in considerable modification to coding and billing procedures.

ICD-10, published by the World Health Organization, has two purposes in the United States. The Centers for Medicare & Medicaid Services (CMS) developed the ICD-10 Clinical Modification (ICD-10-CM) to use in classification of a diagnosis and reasons for visits in all U.S. healthcare settings. It also developed the ICD-10 Procedure Coding System for procedural coding of hospital inpatient care. However, providers will continue to use Current Procedural Terminology (CPT) codes. This article concerns only ICD-10-CM (referred to as ICD-10 in this article).

Differences Between ICD-9 and ICD-10
ICD-10 significantly increases the number of codes: ICD-9 has approximately 14,000 codes, whereas ICD-10 increases that number to approximately 69,000 (Table 1). These additional codes allow clinical providers to better capture specificity in disease states. For example, in a diagnosis of acute respiratory failure, ICD-10 adds digits to the right of the decimal (Table 2). ICD-10 also allows the use of holder (X) spaces to allow for future expansion.

The decision to increase the quantity of characters in a single code allows for a more succinct description of a particular disease and adds in codes for laterality (the side of the body in which the disease manifests). More than 40% of ICD-10 codes designate the patient’s right or left side. The range of severity parameters also is broader in ICD-10, as compared to ICD-9.

In addition to the increase in specificity, ICD-10 contains codes that combine common conditions. For example, ICD-10 code I25.110 applies to the combination of atherosclerotic heart disease of native coronary artery with unstable angina pectoris, a condition that would require two ICD-9 codes to describe. ICD-9 codes allowed the use of only three to five characters, whereas ICD-10 expands that number to seven characters (Figure 1).

​While the number of characters might seem daunting, a further examination of the new codes shows that most have no effect on clinical practice. Of the 69,000 codes, approximately 40,000 deal with symptoms associated with injury, poisoning and other external causes, while another 8,000 deal with morbidity reporting or health status.1 Those 48,000 codes are not commonly used in clinical practice.

This leaves approximately 21,000 ICD-10 codes useful for clinical practice, an approximately 50% increase over the ICD-9 codes. The number of new codes used varies widely by the type of practice. For instance, ICD-10 provides for greater specificity in orthopedic codes and adds designations for laterality, so practices with a significant orthopedics component have seen significant changes. By contrast, a typical medical intensive care unit practice sees more codes to increase specificity in pneumonia and diabetes, for example, but not much else.

Let us look at one instance where the number of codes has marginally increased. ICD-9 had four codes for acute respiratory failure, three of which took into account certain modifications, such as acute respiratory failure following trauma and surgery (Table 2). With ICD-10, additional modifiers for hypercapnia and hypoxia double the number of codes to eight—still only an increase of four in that particular diagnosis.

Transition to ICD-10
It is beyond the scope of this article to describe the complete transition to ICD-10. Generally speaking, organizations should have taken steps to ensure that all elements of their billing cycle comply with ICD-10.  These elements include billing software, the billing staff, practice management, and electronic health record vendors. In addition, all organizations must retain close communication with payers to ensure compliant submission of claims in the wake of this transition.

Provider Education
While billing workflow varies, providers and coders have changed, or must change, their methods as a result of this transition. This means staff education is key. To ensure accurate coding, those involved must understand the increased specificity and the addition of laterality. In coding and billing, the translation from one code to another is known as “crosswalk.” One common method used to educate providers about the new codes is giving concrete examples by “crosswalking” the top 50 ICD-9 codes over to the ICD-10 counterparts.

Fortunately, a white paper by athenahealth2 indicates that 73.3% of ICD-10 codes are an approximate or exact match to those in ICD-9, and another 18.7% have one match with multiple choices. Generally speaking, the other 8% either have no mapping at all or require complex mapping.  So 92% of the new codes should be relatively easily to crosswalk.

A number of firms provide commercial applications for crosswalking. For organizations with database capability, CMS publishes General Equivalence Mappings (GEMs), which show crosswalks for 2015 ICD-10 codes.3 Another resource is provided by the American Academy of Professional Coders (AAPC), which has an online ICD-9 to ICD-10 translator tool. Finally, CMS has an ICD-10 lookup tool.

These aids help to crosswalk commonly used codes and consequently generate updated sets. Organizations that use superbills can convert these in a similar manner. After crosswalking superbill codes, the provider can produce a claim that is compliant with ICD-10.

This significant change to the billing cycle involved multiple intermeshed agencies. As such, the introduction of ICD-10 has initially created significant strain on healthcare organizations. Ensuring that all billing elements comply with ICD-10 is vital to ensure proper documentation.


1.  Steindel S. Taking ICD-10-CM in parts. Accessed June 2, 2015.
2.  athenahealth. Making a smooth transition: avoiding the top 5 risks of the ICD-10 conversion. December 2014. Accessed September 17, 2015.
3.  Centers for Medicare and Medicaid Services. 2015-ICD-10-CM and GEMs. Accessed June 2, 2015.