What is ICD-10-CM?

ICD-10-CM is the current diagnosis code set used in the United States, effective October 1, 2015.  You may also hear about ICD-10-PCS (Procedure Coding System), another code set used for inpatient hospital procedures.  ICD-10-PCS will be discussed in FAQ 9 below.  

The International Classification of Diseases (ICD) is the copyrighted official publication of the World Health Organization (WHO). The primary purpose of ICD is for epidemiological tracking of illness and injury. ICD has been used in the US since 1949 (ICD­-6). The US version of ICD is managed by the National Center for Healthcare Statistics (NCHS) of the CDC with additional oversight by the cooperating parties: Centers for Medicare and Medicaid Services (CMS), American Hospital Association (AHA), and American Health Information Management Association (AHIMA). ICD-10-CM is the HIPPA transaction code set for diagnosis coding. The ICD-10-CM Official Guidelines for Coding and Reporting provides the rules for using the code set. Answers to questions about ICD-10 code interpretations or applications are published quarterly by the AHA in Coding Clinic for ICD-10 CM/PCS. This information is used by payers and auditors in their reviews of code use.

How is ICD-10 organized?

The ICD-10-CM tabular divides Diseases and Injuries into 21 sections or chapters.  It also contains three index tables for conditions related to 1) Chemicals and Drugs, 2) External Causes of Injury, and 3) Neoplasms which can expedite finding codes for those issues.  Unlike ICD-9-CM, no chapter in ICD-10-CM is considered as supplementary. The table below lists the 21 sections for Diseases and Injuries:


 Alpha Numeric

1. Certain Infectious and Parasitic Diseases


2. Neoplasms  


3. Blood and Blood-forming Organs


4. Endocrine, Nutritional and Metabolic Diseases  


5. Mental, Behavioral, and Neurodevelopmental Disorders  


6. Nervous System  


7. Eye and Adnexa  


8. Ear and Mastoid Process  


9. Circulatory System  


10. Respiratory System  


11. Digestive System  


12. Skin and Subcutaneous Tissue  


13. Musculoskeletal System and Connective Tissue  


14. Genitourinary System  


15. Pregnancy, Childbirth and the Puerperium  


16. Certain Conditions Originating in the Perinatal Period  


17. Congenital Malformations, Deformations and Chromosomal Abnormalities  


18. Symptoms, Signs and Abnormal Clinical and Laboratory Findings  


19. Injury, Poisoning and Certain Other Consequences of External Causes  


20. External Causes of Morbidity  


21. Factors Influencing Health Status and Contact with Health Services  


22. Codes for Special Purposes


Injury codes S00-S99 are listed by anatomical location and type of injury.  The following table illustrates truncated codes by anatomical position and injury type:






Dislocation/ Sprain


Blood Vessel



























Thorax (front/back)











Lower Torso (front/back)











Shoulder & Upper Arm











Elbow & Forearm











Wrist & Hand











Hip & Thigh











Knee & Lower Leg











Ankle & Foot











Most codes related to orthopedic conditions, injuries, poisonings and certain other external causes require a seventh character to indicate the phase of care (see FAQ 4).

Does ICD-10-CM require any testing before making a diagnosis?

No. The provider may make a diagnosis based on the highest level of clinical certainty. The ICD-10-CM Official Guidelines for Coding and Reporting says that choice of diagnostic code(s) is based on the provider’s diagnostic statement that the condition exists. This documentation is sufficient to show a particular condition is present at the encounter.

In ICD-10-CM, how would I report COVID-19 presentations?

General Guidance for coding COVID-19 (effective January 1, 2021):

When the COVID-19 virus is confirmed, code first ICD-10-CM U07.1 COVID-19, followed by the disease, condition or manifestation associated with the COVID-19 virus. “Confirmation” does not require a positive test but may be physician documentation confirming the patient has COVID-19.This includes asymptomatic patients as well. When COVID-19 is the reason for care in a pregnant patient, the pregnancy code O98.5- (Other viral diseases complicating pregnancy, and childbirth), should be sequenced first with confirmed COVID-19 (U07.1) and any manifestation listed as additional diagnoses. For patients with suspected COVID-19 assign codes for the presenting signs and symptoms along with Z20.822 (Contact with and (suspected) exposure to COVID-19).

While there is a code Z11.52, Encounter for screening for COVID-19, it is not to be used during the current PHE. Effective January 1, 2021,the ICD-10-CM Official Guidelines for Coding and Reporting states that code Z20.822 should be used for screening for asymptomatic patients who are suspected to have been exposed to a disease by close personal contact with an infected individual or are in an area where a disease is epidemic, symptomatic patients with a negative test (and not otherwise confirmed by documentation), and pre-operative testing.

Code M35.81 is used for Multisystem Inflammatory Syndrome (MIS). List U07.1 if the patient has confirmed COVID-19 at the time of the encounter. In patients where a previous COVID-19 infection is documented as the cause of the MIS, then list MIS as the first diagnosis and B94.8 (Sequelae of other specified infectious) in addition. If the patient has a known or suspect contact with COVID-19 but no current or previous COVID-19 infection list MIS first and Z20.822 in addition. Be sure to list any manifestations associated with the MIS.

At this writing, there are no specific codes to identify adverse effects, allergic reactions or anaphylaxis specifically for COVID-19 vaccines. For adverse effect(s) of COVID-19 vaccine, code first the manifestation(s) (e.g. fatigue R53.83), and T50.B95A (Adverse effect of other viral vaccines, initial encounter) as additional diagnosis. For anaphylaxis resulting from COVID-19 vaccine, code T80.52XA, followed by other conditions as appropriate. For allergic reaction to COVID-19 vaccine, code first T78.49XA, other allergy, followed by manifestation(s).

Clinical Impression

Code First

Also Code

Confirmed COVID-19 pneumonia



Acute bronchitis due to other specified organisms



Bronchitis , not specified as acute or chronic



Unspecified  acute lower respiratory infection



Respiratory Infection NOS, Other specified resp. disorders



Acute Respiratory Distress Syndrome (ARDS)



Multisystem Inflammatory Syndrome

See above


Pregnancy with confirmed COVID-19



Suspected possible COVID-19 exposure ruled out


Other Conditions

Exposure to someone confirmed to have COVID-19


Other Conditions

Personal History of COVID-19

Other Conditions


Anaphylaxis due to COVID-19 vaccine


Other Conditions

Allergic Reaction to COVID-19 vaccine



Adverse effect COVID-19 vaccine



ICD-10-CM Official Guidelines for Coding and Reporting FY 2022

ICD-10-CM Codes for COVID-19, Dec. 3, 2020, Effective Jan. 1, 2021

AHIMA and AHA FAQ: ICD-10-CM/PCS Coding for COVID-19 [Updated 8-27-2021]

In ICD 10-CM, how would a common diagnosis such as “ACS” be coded?

An important principle of coding is to use the diagnosis which best describes your clinical impression and to be as specific as possible. For example, using a non-specific diagnosis of “chest pain” (which codes to R07.9 “chest pain, unspecified”) is much less specific then using “precordial pain” (R07.2) when using a symptom code. On the other hand, ICD-10 includes several specific diagnoses such as unstable angina, STEMI, and NSTEMI (I20-21 for initial cardiac insult) which should be used when applicable.  Acute coronary syndrome (ACS) codes at I24.9 (Acute ischemic heart disease, unspecified). Additional codes are available to indicate presence or absence of additional risk factors, e.g. patient smokes, is an ex-smoker, or never smoked.

In ICD 10-CM, how would a traumatic fracture from a trampoline fall be coded?

Orthopedic codes represent about 25% of codes found in ICD-10. It is important to clearly specify where the fracture is located (e.g. ramus of right mandible), and laterality (e.g. right ilium). In the example of an ankle fracture, it is important to describe whether it was displaced or nondisplaced, and whether it was a fracture of the medial malleolus, lateral malleolus, bi-malleolar or tri-malleolar fracture of the right or left lower leg.  For example, a non-displaced right lateral malleolar fracture would be coded to S82.64XA. Additional codes that could be extracted from your documentation would specify if the fracture resulted from a fall (e.g. W17.89XA Other fall from one level to another, initial encounter), and even the location of the fall or activity (e.g. Y93.44 Activity, trampolining) when you provide these details in your ED note.

ICD-10 Guidelines provide that fractures not specified as displaced or non-displaced should be coded to displaced.  Fractures not specified as open or closed are coded to closed.  The ICD-10 codes for fractures use a 7th character to indicate, among other things, initial versus subsequent encounters for fractures.  Initial encounter is used while the patient is receiving active treatment for the fracture.   Initial encounter may also be assigned when a patient is transferred to another facility (e.g. trauma center) for higher level of care during the period of active treatment. A subsequent visit code would be used if an x-ray was being obtained to check healing status of fracture or if there was only a cast change or removal.  Documentation for subsequent encounters should describe routine healing, delayed healing, malunion or nonunion of fractures.  The suffix “S” for sequela is appropriate for other late effect manifestations or complications of an injury, exclusive of delayed healing, malunion or nonunion of fractures.

How are poisoning, adverse effect and under dosing codes sequenced?

Codes T36-T50 describe poisoning by, adverse effect of, and under dosing of drugs, medications, and biological substances.   These are combination codes which include both the substance that was taken as well as the intent (e.g. accidental, intentional self-harm, undetermined).  No additional external cause code is required for this code set.  A poisoning code (accidental, intentional self-harm, assault and undetermined intent) may be a primary code, with manifestations sequenced following the poisoning code.  For example, intentional overdose of benzodiazepine with intent to self-harm, resulting in respiratory failure with hypoxia would be sequenced as follows:

  1. T42.4X2A (Poisoning by benzodiazepines, intentional self-harm, initial encounter)   
  2. J96.01 (Acute respiratory failure with hypoxia)   

For adverse effect of a drug that has been correctly prescribed and properly administered, assign code(s) which describe the nature of the adverse effect (manifestation), followed by the appropriate code from the T36-T50 code set.  For example, new onset urticaria due to Lisinopril would be sequenced as follows:

  1. L50.8 (Other urticaria)   
  2. T46.4X5A (Adverse effect of angiotensin-converting-enzyme inhibitors, initial encounter)   

 ICD-10-CM introduced a code set for under dosing of medications, which is defined as taking less of a medication than is prescribed by a provider or a manufacturer’s instruction.  Under dosing codes should never be assigned as principal or first-listed codes.  For example, intractable generalized epileptic seizure, prescribed Dilantin with lab phenytoin level 4 ug/ml would be coded:

  1. G40.319 (Generalized idiopathic epilepsy and epileptic syndromes, intractable, without status epilepticus)   
  2. T42.0X6A (Underdosing of hydantoin derivatives)   

Additional ICD-10-CM codes are available to describe under dosing intent as documented:


Patient’s intentional under dosing of medication regimen due to financial hardship


Patient’s intentional under dosing of medication regimen for other reason


Patient’s unintentional under dosing of medication regimen due to age-related disability


Patient’s unintentional under dosing of medication regimen for other reason


How to I code if there isn’t a “diagnosis” or any clinical findings?

Signs and symptoms may be coded when there isn’t a specific diagnosis. For example, a patient who has a fever, nausea and vomiting, without other clinical findings, code fever (R50.9) and nausea with vomiting (R11.2).

Codes for suspected diseases and conditions ruled out (Z03-Z05) may be used when a patient is being evaluated for a suspected abnormal condition, that presents without any signs or symptoms. For example, a parent brings their child concerned that the child may have gotten into a prescription medicine. The child is symptom free and diagnostic testing is negative. In this case you would code Z03.6 (Encounter for observation for suspected toxic effect from ingested substance ruled out).

How do I code if a patient is brought in for an alcohol or drug test?

If this is the only reason for the visit use code Z02.83 (Encounter for blood-alcohol and blood-drug test). Code also for any positive test results, for example, R78.1 (Finding of opiate drug in blood).

Will there be updates and revisions to ICD-10-CM?

The ICD-10 Coordination and Maintenance Committee (C&M) is a Federal interdepartmental committee comprised of representatives from the Centers for Medicare and Medicaid Services (CMS) (who are responsible for PCS codes) and the Centers for Disease Control and Prevention's (CDC) National Center for Health Statistics (NCHS) (who are responsible for CM codes).  Each agency is responsible for approving coding changes, developing errata, addenda and other modifications within their area of responsibility.  Requests for coding changes are submitted to the committee for discussion at either the Spring or Fall C&M meeting. Almost all ICD-10-CM code additions and changes come from medical specialty societies or health care related groups. A public comment period follows which helps guide the agencies whether to accept, deny or modify the code proposals. 



Requests for code changes to ICD-10-CM can be made by individuals or directed to the Coding and Nomenclature Advisory Committee. Comments on proposals from a Coordination and Maintenance Committee meeting or requests for new/modified codes should be directed to: National Center for Health Statistics, ICD-10-CM Coordination and Maintenance Committee,,

Are "unspecified" diagnosis codes permitted with ICD-10-CM?

Yes, these types of codes are permitted when a more specific diagnosis is not available at the time of the encounter. For example, if the patient is diagnosed with a pneumonia but the physician is not able to determine additional detail then "Pneumonia, organism unspecified" (J18.9) is a permissible diagnosis. However, if the pneumonia was associated with aspiration of vomit (J69.0) or Avian influenza (J09.X1), then those specific codes would be used.

Specificity is of particular importance, for example, as to the location of an injury, abdominal, back or limb pain. A specific diagnosis should indicate if an injury was of the left/ right forearm or upper arm or 3rd digit finger as opposed to non-specific term "arm" or "finger." Diagnoses that do not list laterality when applicable, e.g. left vs. right, are more likely to be denied. For example, listing the diagnosis as “ankle sprain” (S93.409 Sprain of unspecified ligament of unspecified ankle) is more likely to elicit prepayment review than “right ankle sprain” (S93.401 Sprain of unspecified ligament of right ankle). The EP may not be able to tell which specific ligament is involved (e.g. calcaneofibular vs. tibiofibular) but should be able to note which side is affected.

The ICD-10-CM Official Guidelines for Coding and Reporting says:

Signs/symptoms and "unspecified" codes have acceptable, even necessary, uses. While specific diagnosis codes should be reported when they are supported by the available medical record documentation and clinical knowledge of the patient's health condition, there are instances when signs/symptoms or unspecified codes are the best choices for accurately reflecting the healthcare encounter. Each healthcare encounter should be coded to the level of certainty known for that encounter.

If a definitive diagnosis has not been established by the end of the encounter, it is appropriate to report codes for sign(s) and/or symptom(s) in lieu of a definitive diagnosis. When sufficient clinical information isn't known or available about a particular health condition to assign a more specific code, it is acceptable to report the appropriate "unspecified" code (e.g., a diagnosis of pneumonia has been determined, but not the specific type). Unspecified codes should be reported when they are the codes that most accurately reflect what is known about the patient's condition at the time of that particular encounter. It would be inappropriate to select a specific code that is not supported by the medical record documentation or conduct medically unnecessary diagnostic testing in order to determine a more specific code. (Section I.B.18, underline added)

This information was also published in AHA Coding Clinic® for ICD-10-CM/PCS, Second Quarter 2013, pages 29-30.

Payers may need to be reminded, "Adherence to these guidelines when assigning ICD-10-CM diagnosis and procedure codes is required under the Health Insurance Portability and Accountability Act (HIPAA)."  (ICD-10-CM Official Guidelines for Coding and Reporting) Additional coding guidance is published quarterly in AHA Coding Clinic® for ICD-10-CM/PCS.

Are External Cause Codes required for ICD-10-CM?

There is no national requirement for mandatory ICD-10-CM external cause code reporting. Unless you are subject to a State-based external cause code reporting mandate or these codes are required by a particular payer, you are not required to report ICD-10-CM codes found in Chapter 20 of the ICD-10-CM, External Causes of Morbidity. Check with your local payers to determine whether they require external cause codes. However, it is not unreasonable that this information would be part of the ED documentation and could be extracted by the hospital or other party as required.

What is ICD-10-PCS?

ICD-10-PCS (Procedure Coding System) is designed to replace Volume 3 of ICD-9-CM. As with ICD-9, ICD-10-PCS is ONLY used by hospitals to show inpatient resource utilization. It does not affect services provided in the outpatient setting, including the ED. It is not intended to show physician work, and CMS has stated ICD-10-PCS is not intended to replace CPT for physicians procedure coding.

CPT remains the procedure coding standard for physicians, regardless of whether the physician services were provided in the inpatient or outpatient setting. Any third party payer asking for ICD-10-PCS procedure codes to be submitted along with CPT codes for outpatient services is in violation of HIPAA regulations and subject to fines by CMS.

Where can I learn more about ICD-10-CM and ICD-10-PCS?

For requests to update the ICD-10-CM codes, please note The National Center for Healthcare Statistics of the CDC is responsible for the development and maintenance of ICD-10-CM. Please send your ICD-10-CM comments to:  National Center for Health Statistics, ICD-10-CM Coordination and Maintenance Committee,

ICD-10-CM Official Guidelines:

ICD-10-CM Search Tool:

ICD-10 Fee-For-Service educational resources, including MLN Matters® articles, MLN products, MLN Connects® videos, and CMS resources: on the CMS website

For questions about Claims Processing and Payment or Local Coverage Determinations:

Contact your Medicare Administrative Contractor (MAC) for guidance. You can find the list of MACs at this link: 

Additional resources are located on the ACEP website: 

ICD-10-CM and the Emergency Physician

ICD-10-CM For the Busy Emergency Physician

ICD-10-CM ED Clinical Examples

Updated March 2022


The American College of Emergency Physicians (ACEP) has developed the Reimbursement & Coding FAQs and Pearls for informational purposes only.   The FAQs and Pearls have been developed by sources knowledgeable in their fields, reviewed by a committee, and are intended to describe current coding practice. However, ACEP cannot guarantee that the information contained in the FAQs and Pearls is in every respect accurate, complete, or up to date.

The FAQs and Pearls are provided "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. Payment policies can vary from payer to payer. ACEP, its committee members, authors, or editors assume no responsibility for, and expressly disclaim liability for, damages of any kind arising out of or relating to any use, non-use, interpretation of, or reliance on information contained or not contained in the FAQs and Pearls. In no event shall ACEP be liable for direct, indirect, special, incidental, or consequential damages arising from the use of such information or material. Specific coding or payment-related issues should be directed to the payer.

For information about this FAQ/Pearl, or to provide feedback, please contact David A. McKenzie, ACEP Reimbursement Director, at (469) 499-0133 or

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