Risk of Duplicate ICD Codes for Orthopedic and Injury Related Research

Abstract

The World Health Organization's International Classification of Diseases (ICD) has become the international standard diagnostic classification for reporting morbidity and mortality. In 2015, the United States transitioned from the 9th to 10th Revision. The update was necessary due to major structural limitations of the ICD-9 system. Concerns of the transition mainly centered around clinical usage and cost; however, there were concerns for overlapping codes with the same classification but different meanings between the two versions. Duplicate codes could pose an issue for big data retrospective studies that overlap between the two systems. Therefore, the goals of this study are to further explore and identify duplicate ICD codes between the systems. ICD-9-CM and ICD-10-CM code files were obtained from the Centers for Medicare & Medicaid Services. There were 14,567 ICD-9-CM codes and 91,737 unique ICD-10-CM codes tabulated. Duplicated items between the files were isolated. Four hundred sixty-nine duplicate codes were identified, consisting of 39 E Codes and 430 V Codes. These twin codes contain classifications for external causes of injury and factors influencing health status and contact with health services. Therefore, special attention should be drawn to retrospective research involving methods of injury spanning ICD-9 and ICD-10 systems.

Introduction

The World Health Organization's (WHO's) International Classification of Diseases (ICD) has become the international standard diagnostic classification for disease.¹ The classification system allows for the systematic analysis, interpretation, and comparison of morbidity and mortality data collected in different areas at different times.² Beginning in 1893 with the first version of international classification of diseases, the system for classifying diseases has evolved from 179 to over 120,000 total codes in the most recent version.^3,4

On October 1, 2015, the US Department of Health and Human Services began requiring hospitals to report diagnoses and procedures using the 10th revision of International Classification of Diseases (ICD-10-CM/PCS). The ICD-9-CM coding system includes approximately 14,000 diagnosis code, whereas the updated ICD-10-CM coding system contains nearly 70,000 diagnosis codes.⁵ The development of a 10th revision introduces alphanumeric codes and greater specificity than ICD-9.⁶ The update was crucial because of major structural limitations of ICD-9-CM that could no longer adequately accommodate important disease and procedure concepts.⁷ However, the transition from the 30-year-old ICD-9 coding system presented several concerns and challenges.^8-13 While most of the concerns were centered around clinical usage and cost, there were concerns for overlapping codes with the same classification but different meanings between the two versions.¹⁴

From 2014-2017, there have been 39 ICD codes identified as duplicates by the Centers for Medicare & Medicaid Services (CMS). Duplicate codes could pose an issue for retrospective studies that overlap between the transition of the ICD-9 coding system to the ICD-10 coding system. The identified codes involve external cause of injury classifications (e.g., car accident); therefore, studies exploring injury research or evaluation of injury prevention strategies could be impacted. To date, no studies have investigated duplicate ICD codes and their influence on big data collection. The aims of this study are to: 1) provide background on duplicate codes published by the CMS, and 2) investigate if there are additional duplicate codes based on CMS classification.

Methods

Microsoft Excel files containing official ICD-9-CM and ICD-10-CM codes were downloaded from the CMS website.^15,16 The codes were compiled into one sheet and tabulated. A function was set up to only select duplicate codes. These codes were isolated and transferred to a separate Excel file. This study is exempt from review by the Institutional Review Board because the data is publicly available.

Results

Duplicate ICD-9-CM and ICD-10-CM Codes

14,567 ICD-9-CM codes and 91,737 unique ICD-10-CM codes were tabulated. Between the two coding systems, there were 469 duplicate codes.

E Codes

Of the 469 codes, there were 39 E Codes (Table 1). The ICD-9 codes classify external cause of injury, while the ICD-10 codes classify metabolic disorders.

Table 1.

List of Duplicate ICD E Codes

ICD-9	ICD-9-CM code title	ICD-10	ICD-10-CM code title
E030	Unspecified activity	E030	Congenital hypothyroidism with diffuse goiter
E8020	Railway accident involving derailment without antecedent collision injuring railway employee	E8020	Unspecified porphyria
E8021	Railway accident involving derailment without antecedent collision injuring passenger on railway	E8021	Acute intermittent (hepatic) porphyria
E8029	Railway accident involving derailment without antecedent collision injuring unspecified person	E8029	Other porphyria
E8300	Accident to watercraft causing submersion injuring occupant of small boat, unpowered	E8300	Disorder of copper metabolism, unspecified
E8301	Accident to watercraft causing submersion injuring occupant of small boat, powered	E8301	Wilson's disease
E8309	Accident to watercraft causing submersion injuring unspecified person	E8309	Other disorders of copper metabolism
E8310	Accident to watercraft causing other injury to occupant of small boat, unpowered	E8310	Disorder of iron metabolism, unspecified
E8319	Accident to watercraft causing other injury to unspecified person	E8319	Other disorders of iron metabolism
E8330	Fall on stairs or ladders in water transport injuring occupant of small boat, unpowered	E8330	Disorder of phosphorus metabolism, unspecified
E8331	Fall on stairs or ladders in water transport injuring occupant of small boat, powered	E8331	Familial hypophosphatemia
E8332	Fall on stairs or ladders in water transport injuring occupant of other watercraft – crew	E8332	Hereditary vitamin D-dependent rickets (type 1) (type 2)
E8339	Fall on stairs or ladders in water transport injuring unspecified person	E8339	Other disorders of phosphorus metabolism
E8340	Other fall from one level to another in water transport injuring occupant of small boat, unpowered	E8340	Disorders of magnesium metabolism, unspecified
E8341	Other fall from one level to another in water transport injuring occupant of small boat, powered	E8341	Hypermagnesemia
E8342	Other fall from one level to another in water transport injuring occupant of other watercraft – crew	E8342	Hypomagnesemia
E8349	Other fall from one level to another in water transport injuring unspecified person	E8349	Other disorders of magnesium metabolism
E8350	Other and unspecified fall in water transport injuring occupant of small boat, unpowered	E8350	Unspecified disorder of calcium metabolism
E8351	Other and unspecified fall in water transport injuring occupant of small boat, powered	E8351	Hypocalcemia
E8352	Other and unspecified fall in water transport injuring occupant of other watercraft – crew	E8352	Hypercalcemia
E8359	Other and unspecified fall in water transport injuring unspecified person	E8359	Other disorders of calcium metabolism
E8381	Other and unspecified water transport accident injuring occupant of small boat, powered	E8381	Hungry bone syndrome
E8389	Other and unspecified water transport accident injuring unspecified person	E8389	Other disorders of mineral metabolism
E8411	Accident to powered aircraft, other and unspecified, injuring occupant of military aircraft, any	E8411	Meconium ileus in cystic fibrosis
E8419	Accident to powered aircraft, other and unspecified, injuring other person	E8419	Cystic fibrosis with other intestinal manifestations
E848	Accidents involving other vehicles, not elsewhere classifiable	E848	Cystic fibrosis with other manifestations
E851	Accidental poisoning by barbiturates	E851	Neuropathic heredofamilial amyloidosis
E8801	Accidental fall on or from sidewalk curb	E8801	Alpha-1-antitrypsin deficiency
E8809	Accidental fall on or from other stairs or steps	E8809	Other disorders of plasma-protein metabolism, not elsewhere classified
E882	Accidental fall from or out of building or other structure	E882	Lipomatosis, not elsewhere classified
E8840	Accidental fall from playground equipment	E8840	Mitochondrial metabolism disorder, unspecified
E8841	Accidental fall from cliff	E8841	MELAS syndrome
E8842	Accidental fall from chair	E8842	MERRF syndrome
E8849	Other accidental fall from one level to another	E8849	Other mitochondrial metabolism disorders
E8881	Fall resulting in striking against other object	E8881	Metabolic syndrome
E8889	Unspecified fall	E8889	Other specified metabolic disorders
E892	Conflagration not in building or structure	E892	Postprocedural hypoparathyroidism
E895	Accident caused by controlled fire in private dwelling	E895	Postprocedural testicular hypofunction
E896	Accident caused by controlled fire in other and unspecified building or structure	E896	Postprocedural adrenocortical (- medullary) hypofunction

V Codes

Four hundred thirty V Codes were identified as duplicates in addition to the E Codes (Supplemental Table 1). The ICD-9 V codes classify factors influencing health status and contact with health services, while the ICD-10 V codes classify external cause of injury. Examples are listed in Table 2.

Table 2.

Examples of Duplicate ICD V Codes

ICD-9	ICD-9-CM code title	ICD-10	ICD-10-CM code title
V700	Routine general medical examination at a health care facility	V700	Driver of bus injured in collision with pedestrian or animal in nontraffic accident
V061	Need for prophylactic vaccination and inoculation against diphtheria-tetanus-pertussis, combined [DTP] [DTaP]	V061	Pedestrian injured in collision with other nonmotor vehicle in traffic accident
V762	Screening for malignant neoplasms of cervix	V762	Person outside bus injured in collision with nonmotor vehicle nontraffic accident
V140	Personal history of allergy to penicillin	V140	Pedal cycle driver injured in collision with heavy transport vehicle or bus in nontraffic accident
V103	Personal history of malignant neoplasm of breast	V103	Person boarding or alighting a pedal cycle injured in collision with pedestrian or animal

Discussion

Several reports highlight the impact of the ICD-10 transition, including effects on productivity, costs, reimbursement, coding accuracy, and patient care.^17-22 However, there is a paucity of literature discussing the implications of the transition on research activities. In addition to the 39 ICD codes published by the CMS, there are 469 codes with the same classification but different code meanings between the two coding systems. All codes are within the E and V sections of the International Classification of Diseases. It is important for researchers and clinicians to be aware of the potential for duplicate codes, as discrepancies could lead to false information used for retrospective studies.

The discussion of possible “twinned” ICD codes began to surface around 2012 regarding the use of codes to classify the external cause of injury.²³ Among the ICD-9 system, external causes of injury codes (classified as E000-E030 and E800-E999) are used as supplemental information to diagnosis codes to provide data for injury research and evaluation of injury prevention strategies.²⁴ E codes capture how the injury, poisoning, or adverse effect happened, the intent, the person's status, the associated activity, and the place where the event occurred.²⁵ In ICD-10-CM, the E codes were moved to Chapter 20: External Causes of Morbidity (V01-Y99).²⁶ In both coding systems, the external cause of injury codes are intended to be used in conjunction with diagnoses codes from other chapters in the corresponding ICD coding system to clarify or specify the nature/cause of diagnosis/condition. While there is no national requirement for mandatory external cause reporting, these codes can provide valuable data for injury research and evaluation of injury prevention strategies. Because of the overlapping nature of E and V codes (Figure 1), there is possibility of duplication between the two coding systems, specifically E800-E999 and V01-V99.

Figure 1.

Conversion of ICD-9-CM Codes to ICD-10-CM Codes with Shaded Area Highlighting Area of Overlap Between the Two Systems

Our study findings of 39 duplicate ICD E codes are consistent with the ICD-CM Duplicate Codes posted by the CMS from 2014-2017.^27,28 Of note, there were three ICD-9-CM codes (E8311, E894, E8981) that are like ICD-10-CM codes (E83110, E8940, E89810). It is important to be aware of similar codes that could lead to errors in big data collection of electronic medical records.

The finding of 430 additional ICD V codes to the published CMS duplication list has not been discussed in previous literature. Within the ICD-9 system, V codes are utilized to classify occasions when circumstances other than a disease or injury are recorded as a diagnosis or problem, such as an encounter to act as an organ donor. As previously mentioned, the V codes among the ICD-10 system are a part of the external causes of morbidity and mortality. This includes environmental events and circumstances as the cause of injury, such as a motor vehicle accident. Most ICD-10-CM External Causes of Morbidity (V01-Y99) codes have a requirement for a seventh character (A, D, or S) to indicate whether the injury or condition being treated is the initial encounter (A), subsequent encounter (D), or sequela (S). For example, V41.7 encodes a diagnosis for person on outside of car injured in collision with pedal cycle in traffic accident. However, the code is invalid if it has not been coded to the full number of digits required for that code.²⁹ In this case, the full code would require seven characters, such as V14.7XXA. While the identified duplicate V codes among ICD-10-CM are considered invalid, this finding is important, as it is possible for incomplete codes to arise during the translation of codes depending on the conversion process utilized.

Moreover, this finding can have implications outside the realm of direct patient care with retrospective research projects that utilize ICD conversions. Studies that involve external cause of injury codes spanning both ICD systems can be implicated. For an example, a study aimed to examine hip fractures due to osteoporosis excludes fractures due to high velocity trauma. To accomplish this, all hip fractures associated with an external cause of injury code indicating high velocity trauma (V01-Y99) would be removed, such as V700 (driver of bus injured in collision with pedestrian or animal in non-traffic accident). If the dataset does not distinguish between ICD-9 or ICD-10, the code of interest might be removed by mistake. In this case, the ICD-10-CM definition of V700 is “routine general medical examination at a health care facility.” Routine medical examination is a much more common event than a bus driver being injured by colliding with an animal and would falsely inflate the ICD-10 code for that high-trauma event. Thus, not only would fractures be inaccurately excluded from the study, but a very large portion of the fractures would also be excluded. Because of this possibility, it is important for large-scale projects be able to differentiate between which codes are ICD-9-CM and ICD-10-CM. Being able to distinguish between ICD-9 and ICD-10 codes is necessary; however, this brings attention to another issue of using outside resources for code conversion and lack of consistency.

To ease the burden of researchers who need to translate their cohort from ICD-9-CM to ICD-10-CM, the CMS created and maintains the General Equivalent Maps (GEMs) as a tool for conversion between the two versions.³⁰ The GEMs provide information linking codes from one system with codes in the other system, often times described as “crosswalks.”³¹ The GEM crosswalks are bidirectional with “forward maps” converting ICD-9-CM to ICD-10-CM and “backward maps” converting ICD-10-CM to ICD-9-CM. However, the complex relationship between the conversion ICD-9 and ICD-10 codes is not one-to-one mirror images of one another; therefore, the use of GEMs requires informed consideration.^32-36 As a result of the challenging nature of accurate ICD conversions, many researchers rely on automated conversions, such as coding conversion websites. There is variation among conversion website services, and even highly automated conversions require detailed review.³⁷ For instance, ICD-9-CM codes and ICD-10-CM codes, respectively, are generally referenced as numeric codes without a period (e.g., E030) and alphanumeric codes with a period between the numbers (e.g., E03.0). However, there is variable listing of both coding systems with and without periods. This study excluded periods from both coding versions to be consistent with the methodology utilized by the duplicate codes files published by the CMS.^38,39 The complicated translation between GEMs and variations between automated conversion systems highlight the importance of detailed attention as inconsistency can potentially have an impact on study findings.

There are several limitations of this study. First, we are unable to directly assess the impact of duplicate codes in other studies. As there are differences in the accuracy of conversions with forward or backward mapping,⁴⁰ our study findings encourage studies with overlapping ICD codes to disclose the methods of conversion. Furthermore, while there were several studies investigating the accuracy of conversions among specialties of medicine,^41,42 there is a lack of research regarding the impact of ICD-10 transition pertaining to injury related research. We postulate that this may be due to E and V codes being classified as supplemental codes and not necessary for diagnosis. Future studies are warranted to investigate the accuracy of the ICD-10 transition among injury related research, especially due to the potential for duplicate codes to impact the accuracy of findings among this area of research. Lastly, ICD-9-CM and ICD-10-CM codes were used without periods, which could impact the generalizability of the results to conversions utilizing periods among ICD-10-CM codes. However, we believe this should not limit our findings, as this method was consistent with the duplicate codes file published by the CMS.

With the implementation of another revision, ICD-11, it is important that all data is understood. This topic becomes even more important with the possibility of three different coding systems spanning bioinformatics and hospital administrative data.

Data Availability

ICD-9-CM and ICD-10-CM can be obtained from CMS website with the following links, respectively, https://www.cms.gov/Medicare/Coding/ICD9ProviderDiagnosticCodes/codes and https://www.cms.gov/Medicare/Coding/ICD10/2015-ICD-10-CM-and-GEMs.

Conflicts of Interest

The author declares no conflict of interest.

Funding Statement

This research received no external funding.

Acknowledgments

I would like to acknowledge and thank Bruce Benes for assisting with excel formatting and functions.

Supplementary Materials

The following are available online: Table S1: Master List of Duplicate ICD-9-CM and ICD-10-CM Codes.

Author Biography

Gregory Benes (gbenes@lsuhsc.edu) is a medical student at the Louisiana State University Health Sciences Center School of Medicine.

Table 1.

Examples of Duplicate ICD V Codes

ICD-9	ICD-9-CM code title	ICD-10	ICD-10-CM code title
V700	Routine general medical examination at a health care facility	V700	Driver of bus injured in collision with pedestrian or animal in nontraffic accident
V061	Need for prophylactic vaccination and inoculation against diphtheria-tetanus-pertussis, combined [DTP] [DTaP]	V061	Pedestrian injured in collision with other nonmotor vehicle in traffic accident
V762	Screening for malignant neoplasms of cervix	V762	Person outside bus injured in collision with nonmotor vehicle nontraffic accident
V140	Personal history of allergy to penicillin	V140	Pedal cycle driver injured in collision with heavy transport vehicle or bus in nontraffic accident
V103	Personal history of malignant neoplasm of breast	V103	Person boarding or alighting a pedal cycle injured in collision with pedestrian or animal