ICD-9-CM to ICD-10-CM Conversion


The International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) is a morbidity classification published by the United States for classifying diagnoses and reason for visits in all health care settings. The ICD-10-CM is based on the ICD-10, the statistical classification of disease published by the World Health Organization (WHO). Deaths have been coded using asthma diagnostic codes (ICD-9 Code: 493; or ICD-10 Codes: J45, J46) as the underlying causes of death. However, a clinical modification of the classification for morbidity purposes has been developed by the National Center for Health Statistics (NCHS), the federal agency responsible for use of the International Statistical Classification of Diseases and Related Health Problems, 10th revision (ICD-10-CM) in the United States. 1

General Changes

The ICD-10-CM code sets have updated medical terminology and disease classifications, thus ICD-9-CM and ICD-10-CM are vastly different. There are nearly 5 times as many diagnosis codes in ICD-10-CM than in ICD-9-CM. The clinical modification represents significant changes from ICD-9-CM to ICD-10-CM which include:

  • the addition of information relevant to ambulatory and managed care encounters
  • expanded injury codes
  • the creation of combination diagnosis/symptom codes to reduce the number of codes needed to fully describe a condition
  • the addition of sixth and seventh characters
  • incorporation of common 4th and 5th digit sub-classifications
  • laterality (side of the body affected)
  • improved specificity in code assignment.2

The new structure will allow further expansion than was possible with ICD-9-CM. The ICD-9-CM to ICD-10-CM conversion will have a significant impact on public health surveillance systems and activities that involve coded clinical data and healthcare utilization data, particularly asthma-related hospital discharge and emergency department visits. 2

Coding Changes

  • The ICD-CM codes for asthma have changed from 493.00 – 493.99 in ICD-9-CM to J45.0 – J45.998 in ICD-10-CM (Table).3, 4
  • Asthma codes under ICD-9-CM were stratified by extrinsic (493.00 – 493.02) and intrinsic (493.10 – 493.20)
  • ICD-10-CM codes are stratified by severity
    • mild intermittent asthma (J45.20 – J45.22)
    • mild persistent asthma (J45.30 – J45.32)
    • moderate persistent asthma (J45.40 – J45.42)
    • and severe persistent asthma (J45.50 – J45.52)
  • A few codes covered under the ICD-9-CM asthma codes 493.00-493.99 are not covered under asthma’s J45 codes in ICD-10-CM. Under ICD-10-CM, co-morbidities are typically coded separately.
    • In ICD-9-CM, asthma with chronic obstructive pulmonary disease is coded as chronic obstructive asthma, unspecified (493.20), chronic obstructive asthma with status asthmaticus (493.21), and chronic obstructive asthma with (acute) exacerbation (493.22).
    • Under ICD-10-CM, these aforementioned asthma conditions are coded separately and are included under the codes for chronic obstructive pulmonary disease (J44.0 – J44.9), specifically J44.1 and J44.9.  These codes are not specific to asthma and they include chronic airway obstruction, obstructive bronchitis without acute exacerbation and obstructive bronchitis with acute exacerbation.

Analysis Guidance

The transition from ICD-9-CM to ICD-10-CM occurred on October 1, 2015.  In 2015, asthma hospitalization and emergency department visits data for the first three quarters of the year were coded as ICD-9-CM (493.0-493.9) and the fourth quarter was coded as ICD-10-CM (J45.0-J45.998).  If you received 2015 data with both coding schemes, you will have to differentiate ICD-9-CM and ICD-10-CM records to identify asthma-related hospitalization and emergency department visits. However, if your state coded the complete year (2015) using ICD-9-CM codes, then there will be no change to how data are analyzed and reported.  For both scenarios, trend analysis will require a dash or other symbol indicating a coding change.

By 2016, the transition should be complete and all related data should be coded using ICD-10-CM codes J45.0-J45.998. The change in definition using ICD-9-CM versus ICD-10-CM may result in a decrease in asthma hospitalizations and emergency department visits.


The transition from ICD-9-CM to ICD-10-CM will impact public health surveillance activities, particularly those regarding asthma morbidity and healthcare utilization.  A major challenge for asthma surveillance is the difference in coding for asthma. There will also be a lag in data collection to analyze trends.

The coding and rule changes between ICD-10-CM and ICD-9-CM will result in discontinuities in the measurement of asthma-related morbidity and healthcare utilization outcomes.  A comparability ratio would measure these discontinuities and assist in identifying real changes in morbidity and healthcare utilization. This would be key to understanding the trend in related statistics from 2014 and 2015. 5, 6   To produce this measure, a complete year of 2015 data would need to be coded using ICD-9-CM and ICD-10-CM. A comparability ratio will not be provided by NCHS.

Table: ICD-CM coding for Asthma 3, 4

ICD-CM coding for Asthma (references 3 and 4)
ICD-9-CM codes for Asthma (493.00 – 493.99) ICD-10-CM codes for Asthma (J45.0 – J45.998)
493 asthma
  • 493.0 Extrinsic asthma
    • 493.00 Extrinsic asthma, unspecified
    • 493.01 Extrinsic asthma, status asthmaticus
    • 493.02 Extrinsic asthma, (acute) exacerbation
  • 493.1 Intrinsic asthma
    • 493.10 Intrinsic asthma, unspecified
    • 493.11 Intrinsic asthma, status asthmaticus
    • 493.12 Intrinsic asthma, (acute) exacerbation
  • 493.2 Obstructive asthma
    • 493.20 Obstructive asthma, unspecified
    • 493.21 Obstructive asthma, status asthmaticus
    • 493.22 Obstructive asthma, (acute) exacerbation
  • 493.8 Other forms of asthma
    • 493.81 Exercise-induced bronchospasm
    • 493.82 Cough variant asthma
  • 493.9 Asthma, unspecified
    • 493.90 Asthma, unspecified type, unspecified
    • 493.91 Asthma, unspecified, status asthmaticus
    • 493.92 Asthma, unspecified, (acute) exacerbation
J45 asthma
  • J45.2 Mild intermittent asthma
    • J45.20 Mild intermittent asthma, uncomplicated
    • J45.21 Mild intermit. Asthma, acute exacerbation
    • J45.22 Mild intermit. asthma, status asthmaticus
  • J45.3 Mild persistent asthma
    • J45.30 Mild persistent asthma, uncomplicated
    • J45.31 Mild persistent asthma, (acute) exacerbation
    • J45.32 Mild persistent asthma, status asthmaticus
  • J45.4 Moderate persistent asthma
    • J45.40 Moderate persistent asthma, uncomplicated
    • J45.41 Mod. persistent asthma, (acute) exacerbation
    • J45.42 Mod. persistent asthma, status asthmaticus
  • J45.5 Severe persistent asthma
    • J45.50 Severe persistent asthma, uncomplicated
    • J45.51 Severe persistent asthma, (acute) exacerbation
    • J45.52 Severe persistent asthma, status asthmaticus
  • J45.9 Other and unspecified asthma
    • J45.90 Unspecified asthma
    • J45.901 Unspecified asthma, (acute) exacerbation
    • J45.902 Unspecified asthma, status asthmaticus
    • J45.909 Unspecified asthma, uncomplicated
  • J45.99 Other asthma
    • J45.990 Exercise-induced bronchospasm
    • J45.991 Cough variant asthma
    • J45.998 Other asthma



  1. National Center for Health Statistics [Internet]. Hyattsville: U.S. Department of Health and Human Services; [cited 18 January 2017]. ICD-10-CM Official Guidelines for Coding and Reporting FY 2017. [49 pages] Available from: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2017
  2. National Center for Health Statistics. [Internet] ]. Hyattsville: U.S. Department of Health and Human Services; [cited 2 June 2016]. International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM). [1 page] https://www.cdc.gov/nchs/icd/icd10cm.htm
  3. ICD9Data.com [Internet]. [cited 2 March 2017].   Asthma. [3 pages] Available from: http://www.icd9data.com/2015/Volume1/460-519/490-496/493/default.htm
  4. ICD10Data.com [Internet]. [cited 2 March 2017].   Asthma and Chronic Obstructive Pulmonary Disease. [6 pages] Available from: http://www.icd10data.com/ICD10CM/Codes/J00-J99/J40-J47
  5. Anderson RN, Miniño AM, Hoyert DL, Rosenberg HM. Comparability of cause of death between ICD–9 and ICD–10: Preliminary estimates. National vital statistics reports; vol 49 no. 2.Hyattsville, Maryland: National Center for Health Statistics. 2001.
  6.  National Center for Health Statistics, BC Duggar and W.F Lewis: Comparability of diagnostic data coded by the 8th and 9th revisions of the International Classification of Diseases. Vital/ and Health Statistics. Series 2, No. 104. DHHS Pub. No. (PHS) 87-1378. Public Health Service, Washington. U.S. Government Printing Office July 1987.

Federal and State Contacts and Resources for the ICD-9-CM to ICD-10-CM Conversion

Centers for Disease Control and Prevention (CDC)
National Center for Health Statistics (NCHS)
E-mail: nchsicd10cm@cdc.gov

National Center for Environmental Health (NCEH)
Asthma and Community Health Branch
General Number: (770) 488-3700