CCS Prep

Crosswalks: Walking a Fine Line

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Most people recognize crosswalks as useful tools that serve one of two basic functions: to either map one ongoing system to another (such as CPT codes to/from ICD-9-CM procedure codes) or to assist in learning one system based on how it relates to the system it replaces (such as the CMS DRG system to/from the MS-DRG system crosswalk). But while it may be useful or even necessary to use these crosswalks in the day-to-day functions of a coding professional, it's also important to acknowledge the dangers and pitfalls of using crosswalks.

DRG Crosswalks

With the implementation of the new Medicare Severity (MS) DRG system this year, many in the provider community were happy to see a DRG crosswalk that CMS released along with the Final Rule in the Federal Register, released Aug. 22, 2007. Table 1 illustrates the format and the first four MS-DRGs of this crosswalk.

The crosswalk is definitely a useful tool to assist in learning where cases that were grouped to "old" DRGs will now be grouped under the new system. But note that although the DRG titles appear for the MS-DRGs, there are no DRG titles for the original CMS DRGs. When the crosswalk indicates a one-to-one mapping, as presented in Table 1 for DRGs in the PRE-MDC category, there's no problem. But what happens when two or three CMS DRGs map across to two or three MS-DRGs? This is where the crosswalk has caused confusion. For example, refer to Table 2.

At first glance, it may appear that there is a straight-forward crosswalk from the three CMS DRGs to the three MS-DRGs. If this were true, it would follow that CMS DRG 006 is crosswalked to MS-DRG 040, CMS DRG 007 to MS-DRG 041 and CMS DRG 008 to MS-DRG 042. But refer to the actual titles of the CMS DRGs:

CMS DRG 006: Carpal Tunnel Release

CMS DRG 007: Peripheral & Cranial Nerve & Other Nervous System Procedures with CC

CMS DRG 008: Peripheral & Cranial Nerve & Other Nervous System Procedures without CC

After review of the DRG titles between the two systems, it's apparent that there is no straight-forward, one-to-one crosswalk from one DRG in one system to one DRG in the other. Even though the titles of CMS DRG 008 and MS-DRG 042 are similar (without CC and without CC/MCC), cases in the two DRGs may be significantly different, due to the fact that the CC list was completely revised this year. Cases that are designated as "with CC" this year will be completely different than those designated as "with CC" in previous years.

Another example of the ways in which the crosswalk may be confusing involves the CMS DRGs that were based on patient age. Refer to Table 3.

The titles of CMS DRGs 031, 032 and 033 are as follows:

CMS DRG 031: Concussion, Age Greater than 17 with CC

CMS DRG 032: Concussion, Age Greater than 17 without CC

CMS DRG 033: Concussion, Age 0-17

When CMS developed MS-DRGs, one of the major changes was that the differentiations in the system based on age were eliminated. Thus, there are no MS-DRGs with the terminology of "Age 0-17" or "Age Greater than 17" in their titles. The CMS DRGs with these designations were collapsed down into the base DRGs for that particular subset of DRGs. It's obvious that there is no direct one-to-one crosswalk between the three CMS DRGs and the three MS-DRGs. While the crosswalk is a beneficial tool, the main concept to understand is that a case that previously grouped to one of several CMS DRGs in a subgroup will now group to one of several MS-DRGs in a related subgroup.

Coding Crosswalks

Whenever the phrase "procedure coding" is mentioned, the first question many outpatient coders have is "CPT or ICD-9?" And even though HIPAA guidelines dictate that for hospital coding the ICD-9-CM Volume 3 code set is for inpatient visits only and the CPT code set is for outpatient services only, in reality, many hospitals still require their outpatient coders to assign both sets of codes for outpatient visits. This is for a variety of reasons: in some cases the HIM staff need to access data across service lines and visit types and so require that all procedural services be coded in ICD-9-CM. Of course, the vast majority of payers now require CPT coding for outpatient services, so hospital coders have become extremely proficient in this system as well.

But what happens when coders try to "crosswalk" between the systems? Crosswalking is starting with an already assigned code in one system and then using that information to link to the other system without starting over in the logic stream. While crosswalking is extremely efficient and helpful in many cases, the coder must be aware of certain pitfalls involved in indiscriminate crosswalking. This is not to say that coders should avoid crosswalks, but they should be aware of the hazards and inherent weaknesses in any crosswalked system.

The first step is understanding that the two systems are inherently different. CPT was developed with the medical staff in mind and services are more closely related to those provided by a physician. ICD-9 (particularly the Clinical Modification [CM] version used in the U.S.) includes many services that are provided in a hospital setting, which in some cases reflects non-invasive but still codable procedures. When two such disparate systems are asked to match up, sometimes the result is less than optimal! We're asking the two systems to match to something that in some cases it was never intended to match.

Coders should keep in mind that in many cases there is not a one-to-one match between the systems. For surgical services, CPT is typically more specific and will provide many more codes for a given type of service than ICD-9-CM. The most common example is that of laceration suturing. For the majority of skin and subcutaneous suturing services, one ICD-9-CM code (86.59) is assigned. But the same service may be coded from a much larger group of available codes in CPT, based upon which site of the body is repaired and the extent (depth) of the suturing. This is why more specific information is required for appropriate CPT code assignment. Never try to assign CPT codes based solely on ICD-9-CM procedure codes; in many cases an inappropriate or non-specific code will result. Information that indicates only "excision of a skin lesion" (ICD-9-CM code 86.3) will not crosswalk appropriately to a CPT code, which relies on further information, such as the morphology of the lesion (benign or malignant) and the site from which the excision was taken.

In some cases ICD-9-CM codes exist for services provided in the hospital setting for which there are no corresponding CPT codes. Examples include: indwelling catheter irrigation (96.48), removal of foreign body without incision (98.2X) and pelvic exam without anesthesia (89.26). But be aware that the reverse may also be true. A good example of this relates to burn treatment. Simple small burn treatment, such as that typically provided in the hospital's emergency department (ED), is assigned to code 16020 (Dressings and/or debridement; initial or subsequent; without anesthesia, office or hospital; small). But to assign the appropriate ICD-9-CM procedure code, knowledge of the exact service provided is required because the code assignment is different depending on whether a debridement was provided or merely a simple burn dressing.

Another problem with crosswalked codes is the issue of code terminology that doesn't necessarily match or terms with different definitions. There are a significant number of services with corresponding codes that may reflect the same procedure but have very different code titles and/or definitions.

The coder must understand the underlying concepts behind ICD-9-CM vs. CPT as they relate to different definitions. For example, foreign body (FB) removal from the foot may be coded in several different ways. If no incision is made and the FB is simply pulled from the foot with a forceps or hemostat, no CPT code would be assigned, because those codes assume and require that an incision be made for the procedure to be considered complex enough to assign a code. However, in ICD-9-CM, code 98.28 may be assigned for an FB removal without incision. This is a good example of the lack of a one-to-one relationship or match between the two coding systems. In this case, only an ICD-9-CM code (98.28) would be assigned. Abstracting or other computerized systems must allow the coder to assign one code without the other in cases such as this. The coder must be aware of these guidelines when printed or electronic crosswalks present the full range of choices that include all of these codes. Just because a code appears on a crosswalk does not necessarily mean that it is the appropriate code assignment for every case documented.

In another example, the issue involves toe amputations, and the CPT codes are specifically differentiated depending upon the exact location of the amputation, whether through the metatarsal at the metatarsophalangeal joint or at the interphalangeal joint. The coder should have access to this specific information before attempting to assign the correct code. But note that the ICD-9-CM procedure codes (84.11 and 84.12) are differentiated only by whether only the toe is amputated or the amputation is performed through the foot. There are some crosswalks that link CPT code 28810 (Amputation, metatarsal, with toe, single) to ICD-9-CM code 84.12 (Amputation through foot) because one of the inclusion terms under 84.12 is "transmetatarsal amputation." But if the coder researches further and reviews Coding Clinic for ICD-9-CM, 4th Quarter 1999, p. 19, it's indicated that to assign code 84.12, all toes must be amputated. Code 28810 reflects what's typically documented as a "ray amputation" of a single toe with its corresponding metatarsal head. The Coding Clinic reference clearly directs the coder to ICD-9-CM code 84.11 for this service. There is also an EXCLUDES note under code 84.12 in the ICD-9-CM tabular for "Ray amputation of foot: 84.11."

Coders should not make assumptions about the appropriateness of certain codes based solely on which chapter the code may reside. Some coders assume that only "invasive" or "surgical" types of CPT codes appear in the range between 10021 and 69990. But some invasive services, such as those performed on the cardiovascular system (including cardiac catheterization) reside in the "Medicine" section of CPT. These codes begin with the digit "9" but still may be a part of the HIM coding staff responsibilities. Likewise, some coders may feel that only non-invasive services are represented in Chapter 16 "Miscellaneous Diagnostic and Therapeutic Procedures" of ICD-9-CM Volume 3. But some services that actually do reflect invasive procedures are found here, including foreign body removal that in some cases necessitates an endoscopic approach.

In conclusion, although a crosswalk between DRG systems or ICD-9-CM and CPT are more tools in the coder's arsenal, they should be used with full knowledge that they're not infallible and each DRG and code must be reviewed separately for appropriateness. And coders who will be taking the certified coding specialist (CCS) exams should realize that no such access to any type of crosswalked materials for coding systems will be available for use during the exam. It is necessary and advantageous to be capable of assigning both types of codes individually and independently from one another.

Test your knowledge of crosswalks with the quiz below:

1.The regulation that indicates which code sets are valid for each type of service provided in health care facilities today is:

a. Stark II

b. HIPAA

c. EMTALA

d. All of the above

2.Typically more specific information is necessary to code which of the following type of codes?

a. CPT

b. ICD-9-CM

c. Neither; they require the same level of detail in the documentation

d. HCPCS Level II

3.A patient with an indwelling Foley catheter has been having problems with keeping it clear and draining. He presents to the ED and catheter cleaning and irrigation is performed without replacing the catheter. The service is reported with the following procedure codes:

a. 51700; 96.47

b. 96.47 only

c. 96.48 only

d. 51702; 96.48

4.Which of the following statements is true?

a. Although there are now 745 MS-DRGs, you can usually find one to match each of the old CMS DRGs.

b. Because the numbering systems between CMS DRGs and MS-DRGs are so different, it's impossible to crosswalk "backwards" from CMS to MS-DRGs.

c. The CMS to/from MS-DRG crosswalk may be used as a guide to indicate which DRG subgroup a case will now be grouped to.

d. Although there are no MCCs in the old CMS DRGs, cases designated as "with CC" should match up between the two systems.

This month's column has been prepared by Cheryl D'Amato, RHIT, CCS, director of HIM, Facility Solutions, and Melinda Stegman, MBA, CCS, clinical technical editor, Ingenix (www.ingenix.com), which specializes in the development and use of software and e-commerce solutions for managing coding, reimbursement, compliance and denial management in the healthcare marketplace.

Coding Clinic is published quarterly by the American Hospital Association.

CPT is a registered trademark of the American Medical Association.

Answers to CCS PREP!: 1. b: HIPAA dictated use of ICD-9-CM Volume 3 for inpatient procedures and CPT-4 for outpatient services for hospital-based coding; 2. a: Although there may be some limited examples of ICD-9-CM codes requiring more detail than CPT, the vast majority of CPT codes are more detailed and thus require a higher level of detail in the documentation to assign them appropriately; 3. c: Only code 96.48 (Irrigation of other indwelling urinary catheter) is assigned. The bladder itself was not irrigated so code 51700 is inappropriate and the Foley catheter was not replaced so code 51702 is also inappropriate.; 4. c: The DRG crosswalk should only be used to determine which subgroup a case will be grouped to. There's no one-to-one match between the two systems. There are a number of reverse crosswalks available to the coding community that can map the DRG systems in both directions.


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