Crosswalking In Medical Billing And Coding

Touseef Riaz

August 6, 2021

crosswalking in billing and coding

For years, medical professionals and surgeons had been applying the ICD-9 code set for disease codes and classification. Until the International Statistical Classification of Diseases and Related Health Problems made it mandatory for all medical companies and professionals to shift to the tenth version of the ICD as the previous code set was made obsolete.

Now, transitioning to a new code set that is bigger and more flexible than before is no easy task. First, mapping is used to help professionals compare the differences in codes and necessary documents between the two code sets. The previous code set, in our example the ICD-9, is applied as a comparative reference material till the time medical professionals and physicians are confident with the new code set.

Secondly, crosswalking in medical billing and coding, also called General Equivalence Mappings (GEMs), is applied by medical teams to convert the data from one code set to another, serving as a comprehensive dictionary for translation between the codes.

With the ICD-11 set to arrive and be implemented in the next couple of years, organizations will need to use both mapping and crosswalks to successfully prepare and thus transition to the new code set.

What is Mapping in Medical Coding?

Because of the fact that medical terminology consists of various code sets, it becomes a challenge to translate and understand across the different terminologies. Clinical mapping allows the capture of data in the electronic health record with the terminology best suited as per the situation.

Medical Coding

The mapping works by developing links between concepts between one data set and another similar data set. First, use cases are developed to define the purpose of the mapping, and then rules are established to differentiate the level of details and content as to how the data will be handled between the two data sets.

What is Cross Walking?

To find the similarities and equivalencies between the two data sets requires crosswalking. The different code sets used in medical coding such as ICD, HCPCS and CPT are frequently updated and it is imperative to identify and map the codes that have been changed and updated. Through crosswalking, identical information is mapped across the two data sets.

When crosswalking codes, you perform a coding translation between two sets, not unlike how coders translate medical reports into codes in the first place. The process is used to translate and describe the same thing from the two sets, as crosswalking is not the process of finding the correct diagnosis code for a particular procedure.

Crosswalking is mostly done between two versions of the same code set. The American Medical Association updates the CPT code set every year, where codes are updated, replaced, and deleted. Understanding and recognizing the changes is imperative and can be done through crosswalking.

What is ASA Crosswalk?

All anesthesia services are billed with the CPT codes ranging from 00100-01999, which are crosswalked to surgical codes. The American Society of Anesthesiologists offers their service of Find-A-Code using which crosswalking of anesthesia is made easier.

Using Find-A-Code you can crosswalk from CPT Anesthesia codes to Surgery and Procedure Codes and vice versa. You can also see CMS Base units and ASA Base Units.

Crosswalking between ICD-9 and ICD-10

In recent years, the real crosswalking challenge was the transition from ICD-9-CM to ICD-10-CM. For over two decades, US healthcare had been applying the ICD-9 code set for reporting diagnoses and in the reimbursement process. In 2015, the ICD-9 was effectively replaced by ICD-10 to represent new medical diagnoses.

The ICD-9 Code set consisted of five characters, primarily numeric but with few alphanumeric coders for certain situations. The ICD-10, on the other hand, has seven characters and consists of only alphanumeric codes. Where each ICD-9-CM code could have one subcategory and one sub-classification, and ICD-10-CM code can have one subcategory and two sub-classifications, in addition to an alpha extension that provides information as to which visit, or encounter, this is with the patient’s particular illness or injury. 

Medical Billing

ICD-10-CM is obviously a much more extensive, detail-oriented code set, and its new format and organization presented coders with a challenge during the transition period.

Crosswalk Matches

To begin with the crosswalking process, it is a good practice to break down the types of matches that are possible between the two data sets. When crosswalking between the ICD-9 and ICD-10 code sets, the AMA has defined the following matches for the benefit of coders:

One-To-One Exact Match

This match describes the cases when one code from the source set has an exact match in the target code set.

One-To-One Approximate Matches with One Choice

In these matches, there is a close enough pairing of two codes from the different code sets. When crosswalking between ICD-9 and ICD-10, this type of match makes up the majority of the procedure.

One-To-One Approximate Matches with Multiple Choices

While the first two matches make up most of the crosswalked codes, coders will sometimes run into codes that are less specific to a pair. It is then that an approximate match with multiple choices is applied.

One-To-Many Matches

In one-to-many matches, a single code in one set must be crosswalked to a “cluster” of codes in the other set. Clusters are always between two and four codes. There may be multiple target clusters for a single source code. It’s up to the coder to look at and abstract all of the concepts in the single source code, and find their corollaries in the target code set. This process of crosswalking by cluster requires diligence and a lot of reviews, as a missing code from one of the clusters can drastically affect the status of a claim or report.

No Match

Since the ICD-10 has several diagnosis codes which were not available before in the previous code set, coders may sometimes be faced with a scenario when they have to crosswalk back from ICD-10 to ICD-9 but will not be able to find any match. This will be a no-match case and the phrase ‘NoDX’ may be used to show that there is no target diagnosis code that matches the source code.


During the transition from the ICD-9 code set to the ICD-10-CM, it was crucial for coders to get familiar with crosswalking to better map the new codes. To make the task easier, the National Center for Health Statistics came up with a set of tools called the General Equivalence Mapping or GEMS, that list a code from one set and its exact/appropriate match from the other set.


When transitioning from a previous code set to the new version, one of the foremost things to do for organizations is to invest time and resources to plan out the changes and to have a staff that is well versed in coding and the best practices. Ensuring a focus on timely and accurate documentation as well as the practice of dual coding until the staff is confident and can lead to a seamless transition.

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