ICD-10 Codes Lookup: Complete ICD-10-CM Guide 2027

The data may have been provided in the right manner by the physician, but the ICD-10-CM code submitted could have been overly broad or lacking coding guidelines and, therefore, the wrong one, leading to rejection or denial of the claim.

This explains why selecting ICD-10 codes is not just about looking up for the condition and choosing the first one that pops up.

The medical coder and healthcare provider must know the condition, check the data, and identify the right ICD-10-CM code according to the instruction.

The U.S. ICD-10-CM code system is always being upgraded as well.

The 2027 Diagnosis Code Set (FY 27) will go into effect on October 1, 2026 and will be valid for applicable encounters until September 30, 2027.

How to use an ICD-10 codes lookup, ICD-10 coding instructions, selection of the ICD-10 diagnosis codes, difference between ICD-10-CM and procedure coding systems and many more, and how to avoid common claim errors is covered in this guide.

Whereas, in Medical Coding, what is ICD-10 Code?

ICD-10 codes are regular words that are utilized to identify disease and injury, symptoms and different health related conditions. The clinical modification is used in the United States to report diagnoses and the reason for a health care encounter and the ICD-10-PCS is used to classify procedures performed in hospital inpatient facilities.

ICD: International Classification of Diseases, which is a system of classification used globally by the World Health Organization.

Difference Between ICD-10, ICD-10-CM, And ICD-10-PCS

They do not overlap, but they are connected to each other.

They are connected to each other, but they have different uses.

Coding System	Full Name	Primary Application
ICD-10	International Classification of Diseases, Tenth Revision	International disease classification
ICD-10-CM	International Classification of Diseases, Tenth Revision, Clinical Modification	U.S. diagnosis reporting
ICD-10-PCS	International Classification of Diseases, Tenth Revision, Procedure Coding System	U.S. hospital inpatient procedure reporting
CPT	Current Procedural Terminology	Professional medical services and procedures
HCPCS Level II	Healthcare Common Procedure Coding System, Level II	Additional services, supplies, equipment, and certain products

Even though the information supplied by the doctor can be correct and relevant, when the submitted ICD-10-CM code is not clear enough or if it doesn’t comply with the coding guidelines or if it’s not an acceptable ICD-10 code as for the date of service, the insurance company may either reject or deny the claim.

Thus, the selection of the ICD-10 codes is not merely about finding the right diagnosis and using the first code found.

It’s necessary for the medical coder and the healthcare provider to know the diagnosis, analyze the documentation, and find out the right ICD-10-CM category and its guidelines whether the code can be reported.

The system of ICD-10-CM in the USA undergoes regular changes. On October 1, 2026, there will be the 2027 Diagnosis Code Set (FY 27) and on September 30, 2027, it will take effect.

This guide will be useful for performing ICD-10 codes lookup, ICD-10 coding guidelines understanding, ICD-10 diagnosis codes selection and distinguishing between the ICD-10-CM and procedure coding system.

Medical Coding: What is ICD-10 Code?

ICD-10 codes are ordinary words that describe disease, injury, symptom, and other health-related conditions. ICD-10-CM is the clinical modification used in the USA

The decimal point appears after the third character when a code contains additional characters.

Consider S93.401A, which identifies a sprain of an unspecified ligament of the right ankle, initial encounter.

Its structure illustrates several coding elements:

• S93: Injury category involving joints and ligaments at ankle and foot level.
• .4: Additional category detail for an ankle sprain.
• 01: Further specification involving the right ankle.
• A: Seventh character identifying the initial encounter under the applicable injury coding rules.

The seventh character doesn’t necessarily describe the first time a patient visits a particular physician.

For many injury codes, the initial encounter character applies while the patient is receiving active treatment.

The appropriate character depends on the chapter instructions and circumstances of care.

Understanding Code Specificity

ICD-10-CM often distinguishes between right, left, and unspecified anatomical locations.

Take knee pain as an example.

ICD-10-CM Code	Diagnosis Description
M25.561	Pain in right knee
M25.562	Pain in left knee
M25.569	Pain in unspecified knee
M17.11	Unilateral primary osteoarthritis, right knee
M25.461	Effusion, right knee

These codes don’t describe the same clinical condition.

For encounters without a diagnosis, M25.561 may be coded if the provider documents pain in the right knee without making a diagnosis, according to the guidelines.

If the provider documents and concludes that the right knee has primary osteoarthritis, then the diagnosis M17.11 will be given a different, more specific diagnosis.

It is not right for the coder to make the assumption that a patient that is diagnosed with knee pain will have a note from their clinician that mentions that their knee pain condition is due to osteoarthritis.

In order to properly perform ICD-10 codes lookup, follow these steps:

A reliable ICD 10 codes lookup uses the official coding system rather than relying only on the keyword search results.

Centers for Disease Control and Prevention (CDC) offers an ICD-10-CM Browser to help look up your terms, browse through the list of code categories and instructions.

An official tool is available here: https://icd10cmtool.cdc.gov/ 

The first step in diagnosis is to identify the main diagnosis the next step in the coding process is to identify the principal diagnosis.

Read through the medical record and find out which diagnosis requires coding.

For example, if you have an established diagnosis of Type 2 Diabetes Mellitus and chronic kidney disease, it will be documented as a diagnosis.

Do not use any code related to kidney diseases. Instead, try finding a code of the complications of diabetes and its associated condition.

Go to Step 2 – Alphabetic Index.

Identify the main term in ICD-10-CM Alphabetic Index.

The Alphabetic Index is intended to guide the user to a possible code, but is not sufficient to complete the coding.

Step 2: Run the code to test the desired behavior.

Step 4: Test the desired behavior by running the code in the Tabular List.

Once you have found the candidate code, check this code in the Tabular List.

Check official description, inclusion terms, exclusions, sequencing instructions and any other coding requirements.

This is crucial because a search result might need to be matched with a category, but also further coded for selection.

The fourth step in the process is to look at the documentation and specificity.

Determine whether the documentation supports the selected code.

Information required to make a diagnosis:

Acute or chronic status

Do not include any clinical information that is not documented in the medical record.

Step 5: verify the Applicable Code-Set Year

ICD-10-CM coding is dependent on the date of the service.

The ICD-10-CM release for FY 2027 will take effect on October 1st, 2026.

A code from a previous software may have been updated, added, or removed.

Prior to claiming, be sure the code is valid for that encounter date.

Steps 1-5 are not required. Steps 1-5 are optional.

Use of the right diagnosis codes does not ensure that the codes are in the proper order.

Certain conditions have instructions for sequencing.

For example, some combination codes are followed by other codes for a related manifestation or condition.

Other rules of coding dictate the priority of the diagnosis, depending on the encounter’s purpose.

In step 7, you will review the requirements of payers and claims.

Once coding reviews complete, verify claim’s diagnosis reporting requirements.

For professional claims, diagnosis pointers link procedure lines to applicable diagnosis codes.

Diagnosis reported will require documentation and reimbursement may be subject to medical necessity and/or coverage requirements.

An automated coding edit is not an indicator of whether a service will be covered by the payer.

Official ICD-10-CM Coding Conventions Every Coder Should Know, 2014 Edition. Official ICD-10-CM Coding Conventions Every Coder Should Know 2014 Edition.

That’s where it’s particularly vital to be technically accurate in coding.

Two diagnosis codes may seem like the right choice, one by one, but may need further consideration if they are combined together.

Excludes1 and Excludes2 notes

Exclusion instructions are found in the ICD-10-CM Tabular List.

Excludes excludes diseases which are not related to the condition above the note, and are not included in the code. The official guidelines state that there is an exception if the two conditions are unrelated.

Excludes2: Excluded conditions that do not appear above the note in the code list, but may appear above if the patient has both conditions.

Such notes should be read within the context of the diagnosis and appropriate guidelines.

Write the code and then use the additional code.

There are conditions that have multiple diagnosis codes.

Sequencing requirement is set by a code first instruction if appropriate.

A use of additional code instruction means that there is additional code that needs to be used to give information.

Take a moment to think about diabetic chronic kidney disease.

Code	Description	Role
E11.22	Type 2 diabetes mellitus with diabetic chronic kidney disease	Identifies diabetes with its kidney complication
N18.31	Chronic kidney disease, stage 3a	Identifies the documented CKD stage

When the documentation establishes both conditions, E11.22 and the appropriate N18.- stage code are reported according to the applicable instructions.

The stage code shouldn’t be guessed from an isolated laboratory value without appropriate supporting documentation.

Combination Codes

A combination code is a code that contains two or more related clinical concepts in one code.

For example:

E11.40 – Type 2 Diabetes Mellitus with Diabetic Neuropathy, Unspecified.

Diabetes and diabetic neuropathy are combined in this code.

In case a more precise description of diabetic neuropathy is provided, there exists an alternative code that will describe the disease better.

The documentation should be consulted before selecting an unspecified combination code by the coders.

Placeholders and Seventh Characters.

Some ICD-10-CM categories have 7th characters.

To fill empty character positions, so the required 7th character can be in the proper position, the blank character position is replaced by the placeholder X.

Assignments of an encounter character will follow the code category and official guidelines.

If there is a missing seventh character, then the code may not be valid to report.

NEC and NOS

There are two abbreviations that are used often within ICD-10-CM coding.

NEC — Not Elsewhere Classified: When the documented condition is more specific than the classification choices provided.

NOS — Not Otherwise Specified: Generally indicates that the documentation doesn’t provide enough detail to select a more specific code.

The following terms are intended to clarify why a description of a code which the reader may be unfamiliar with may be appropriate.

The ICD-10 Diagnosis Codes List includes commonly used examples of ICD-10 diagnosis codes.

A useful ICD-10 diagnosis codes list should show coding differences, but not just a long list of hundreds of codes.

Below are examples of common conditions in the U.S. healthcare environment.

ICD-10-CM Code	Diagnosis
I10	Essential (primary) hypertension
E11.9	Type 2 diabetes mellitus without complications
E78.5	Hyperlipidemia, unspecified
J45.909	Unspecified asthma, uncomplicated
M54.50	Low back pain, unspecified
R07.9	Chest pain, unspecified
R51.9	Headache, unspecified
N39.0	Urinary tract infection, site not specified
D72.829	Elevated white blood cell count, unspecified
F32.A	Depression, unspecified
R10.9	Unspecified abdominal pain
Z00.00	Encounter for general adult medical examination without abnormal findings

Examples aside, it is not supposed to serve as an alternative to a full ICD-10-CM book.

It can result in the application of codes that will be different from those of the diagnosis if the provider applies codes depending on the particular complications, locations, severity or underlying conditions.

For example, the code of a diabetic complication that is supposed to be reported should not be reported using E11.9 when there is need to apply other codes to report the complication.

There are codes in the ICD-10-CM Z Codes that are for use when a diagnosis is not the primary reason for the encounter.

Not all health care visits are linked with a particular disease.

Patients also seek services related to personal or family health history, for preventive examinations or screenings, and for follow-up care at the provider.

Many of these circumstances are captured by codes in ICD-10-CM Chapter 21 – codes Z00 – Z99.

Common Z Codes in Medical Billing

ICD-10-CM Code	Description	Coding Context
Z00.00	General adult medical examination without abnormal findings	Routine adult examination
Z00.01	General adult medical examination with abnormal findings	Examination with qualifying abnormal findings
Z12.11	Encounter for screening for malignant neoplasm of colon	Colorectal cancer screening
Z23	Encounter for immunization	Vaccination encounter
Z09	Follow-up examination after treatment for conditions other than malignant neoplasm	Appropriate completed-treatment follow-up
Z85.46	Personal history of malignant neoplasm of prostate	Relevant history of prostate cancer
Z59.82	Transportation insecurity	Documented social determinant of health
Z71.3	Dietary counseling and surveillance	Nutrition-related counseling context

The circumstances of the visit determine whether a Z code can be used as the first-listed diagnosis or must be reported in another position.

For example, Z12.11 describes a screening encounter. It isn’t interchangeable with a diagnosis describing a confirmed colorectal malignancy.

Likewise, personal history codes should not automatically replace active disease codes when a malignancy remains under treatment or is otherwise considered current.

Social Determinants of Health Codes

ICD-10-CM categories Z55–Z65 address many socioeconomic and psychosocial circumstances that may affect health.

For example, Z59.82 identifies transportation insecurity.

These codes may provide useful clinical context when patients face barriers to attending appointments, obtaining medications, or accessing healthcare services.

The official guidelines allow certain social determinants of health codes to be assigned based on documentation by clinicians other than the patient’s provider, or on qualifying patient self-reported information, under the applicable documentation rules.

Accurate SDOH coding depends on what is documented and whether the information meets the relevant requirements.

ICD-10-CM Codes vs. CPT Procedure Codes in Medical Billing

One of the most important billing distinctions is the difference between reporting a condition and reporting the service delivered.

ICD-10-CM answers: Why did the patient receive care?

CPT or HCPCS answers: What service, procedure, or item was provided?

Consider the following illustrative professional billing scenarios.

Clinical Scenario	ICD-10-CM Diagnosis	Potential CPT Service
Established patient evaluated for hypertension	I10	99213, when E/M criteria are met
Patient evaluated for right knee pain	M25.561	99213 or 99214, depending on documented E/M level
Patient receives a medically appropriate ECG during evaluation of chest pain	R07.9	93000, when the complete ECG service is performed and requirements are met
Patient evaluated for uncomplicated type 2 diabetes	E11.9	Appropriate office/outpatient E/M code

These examples illustrate possible diagnosis-to-service relationships, not automatically payable code combinations.

The CPT code must represent the service actually furnished, while the ICD-10-CM code must describe the documented diagnosis or reason for care.

Medical necessity, coverage limitations, payer edits, and documentation requirements still apply.

How Diagnosis Pointers Work

On professional claims, the CMS-1500 form and electronic 837P transaction support diagnosis information and relationships between diagnoses and billed services.

For example, a claim may contain several diagnoses, but not every procedure line is necessarily associated with each diagnosis.

Diagnosis pointers identify which reported diagnoses relate to a particular service line.

Incorrect diagnosis pointers can create medical necessity or claim-processing problems even when the individual codes are valid.

ICD-10-CM Coding for Medical Necessity

A valid diagnosis code doesn’t automatically establish medical necessity.

Insurers may evaluate whether a procedure is covered for a particular condition and whether the medical record supports the reported service.

For Medicare, certain services may be governed by National Coverage Determinations (NCDs) or applicable Local Coverage Determinations (LCDs).

A diagnosis code appearing in a payer’s covered diagnosis list may be relevant, but it doesn’t replace the other requirements of the policy.

Consider a diagnostic imaging claim.

The physician documents the patient’s clinical findings and orders an imaging study.

The diagnosis code should reflect the documented reason for the examination. The coder shouldn’t substitute another diagnosis merely because it appears on a payer’s coverage list.

Accurate coding requires agreement between the medical record, the procedure performed, and the submitted claim.

Common ICD-10 Coding Errors That Lead to Claim Problems

Coding errors can occur during documentation review, code selection, sequencing, or electronic submission.

Coding Problem	Potential Claim Impact	Recommended Correction
Invalid ICD-10-CM code	Claim rejection or denial	Verify the correct code-set release
Missing required seventh character	Invalid diagnosis reporting	Review category-specific character instructions
Unsupported laterality	Coding inconsistency	Confirm the documented anatomical location
Incorrect sequencing	Claim edits or coding compliance issue	Review official sequencing instructions
Missing additional diagnosis code	Incomplete classification	Follow Tabular List instructions
Incorrect diagnosis pointer	Potential coverage or medical necessity problem	Link the procedure to supported diagnoses
Unspecified code despite documented specificity	Coding quality or payer issue	Select the supported, more specific code
Diagnosis not supported by the medical record	Audit or reimbursement concern	Review documentation and query the provider when appropriate

Rejection vs. Denial: What Coders Need to Know

An electronically submitted claim may be rejected because the diagnosis code is invalid or a required claim field is missing.

A claim can also pass the initial acceptance checks and later be denied during adjudication.

For example, a valid ICD-10-CM code may still be associated with a service excluded under the patient’s insurance plan.

The appropriate response depends on whether the claim failed technical validation, contains inaccurate coding, or requires a coverage review.

ICD-10 Coding and Denial Management

After a coding-related denial, review the payer’s explanation rather than automatically changing the diagnosis.

Claim Adjustment Reason Codes (CARCs) and Remittance Advice Remark Codes (RARCs) help communicate payment and adjustment information.

Two examples include:

CARC 16: The claim or service lacks information or contains submission or billing errors needed for adjudication.

CARC 50: The services are noncovered because the payer does not consider them medically necessary.

CARC 16 may require investigation of missing or incorrect claim information, with associated remark codes providing greater detail.

CARC 50 may require examination of the coverage policy, documentation, and available appeal options.

Neither adjustment code proves by itself that the diagnosis was selected incorrectly.

The practice should determine the actual cause before changing and resubmitting a claim.

ICD-10-CM Coding for Inpatient and Outpatient Encounters

Diagnosis selection differs depending on the healthcare setting.

Outpatient Coding

In outpatient settings, uncertain diagnoses generally aren’t coded as though they were confirmed.

Terms such as probable, suspected, or rule out may require reporting the documented signs, symptoms, or other reasons for the encounter instead.

For example, a patient evaluated for chest pain without an established definitive diagnosis may be reported using an appropriate symptom code such as R07.9, depending on the documentation.

Inpatient Coding

Hospital inpatient coding follows different rules for uncertain diagnoses documented at discharge.

Under applicable inpatient guidelines, certain qualifying uncertain diagnoses may be coded as though established.

The inpatient principal diagnosis is selected according to the condition established after study to be chiefly responsible for the admission, with applicable exceptions and instructions.

Present on Admission Reporting

For applicable inpatient claims, Present on Admission (POA) indicators identify whether reportable diagnoses were present at the time of the inpatient admission order.

POA reporting requirements include exceptions and exempt codes.

The indicator should not be confused with the date a diagnosis was first documented in the chart.

Correct inpatient diagnosis coding also affects the information used in Medicare Severity Diagnosis Related Group (MS-DRG) processing.

ICD-10-CM Updates for FY 2027

The FY 2027 ICD-10-CM code set became effective October 1, 2026.

It applies to relevant healthcare encounters and discharges occurring from October 1, 2026, through September 30, 2027.

Healthcare providers should use the official FY 2027 resources when coding services within that period.

Key resources include the Alphabetic Index, Tabular List, official coding guidelines, code descriptions, addenda, and relevant POA exemption materials.

What Should Practices Check After an ICD-10 Update?

First, identify codes that have been added, deleted, revised, or expanded.

Next, review whether the changes affect diagnoses commonly reported by the practice.

Pay particular attention to documentation requirements when an existing category becomes more specific.

Finally, update coding software, EHR diagnosis lists, claim edits, and any internal coding references that depend on the previous release.

Practices should not assume that every code used during FY 2026 is still valid or unchanged in FY 2027.

Best ICD-10 Lookup Resources for Healthcare Providers

A coding reference should provide more than a list of search results.

It should allow users to check the official code description, relevant year, inclusion and exclusion instructions, and associated sequencing requirements.

CDC ICD-10-CM Browser Tool

The CDC browser provides access to official U.S. diagnosis classification information.

It supports code searches, index navigation, tabular review, and selection of relevant fiscal-year versions.

This is a strong starting point for confirming diagnosis codes.

CMS ICD-10 Resources

CMS publishes ICD-10-CM and ICD-10-PCS resources, official guideline links, and implementation materials.

These documents are particularly important when reviewing Medicare coding requirements or changes to the applicable classification.

Professional Coding Software

Commercial coding tools may provide enhanced terminology searches, coding edits, reference content, and workflow integration.

Some products marketed around smart ICD 10 search use predictive suggestions or natural-language processing to locate candidate codes.

These functions can help narrow a search, but suggestions must still be checked against official coding instructions and the medical record.

A convenient search result isn’t the same thing as a validated coding decision.

ICD-10-CM Coding Checklist Before Claim Submission

A consistent review process can prevent many coding-related errors.

1. Confirm that the diagnosis is supported by the provider’s documentation.
2. Locate the condition in the Alphabetic Index.
3. Verify the proposed code in the Tabular List.
4. Check applicable inclusion, exclusion, and sequencing notes.
5. Confirm required specificity, laterality, and encounter characters.
6. Apply additional-code instructions when appropriate.
7. Verify that the code is valid for the date of service.
8. Confirm diagnosis-to-procedure relationships and claim pointers.
9. Review any relevant payer coverage or medical necessity requirements.
10. Submit the claim and monitor acknowledgments and adjudication results.

The checklist won’t replace clinical documentation or professional coding judgment, but it provides a repeatable way to identify avoidable claim issues.

Frequently Asked Questions About ICD-10 Codes

What are ICD-10 codes used for?

ICD-10 codes classify diseases and health-related conditions. In U.S. medical billing, ICD-10-CM diagnosis codes are used to report diagnoses, symptoms, and reasons for encounters on healthcare claims.

How do I perform an ICD 10 codes lookup?

Use an authoritative coding resource such as the CDC ICD-10-CM browser. Search the condition in the Alphabetic Index, confirm the candidate code in the Tabular List, and review instructional notes before reporting it.

What is the difference between ICD-10 and ICD-10-CM?

ICD-10 is the international disease classification. ICD-10-CM is the U.S. clinical modification used for diagnosis reporting and includes the structure and specificity required for American healthcare coding.

Where can I find an official ICD-10 diagnosis codes list?

The CDC provides official ICD-10-CM coding resources and a searchable browser. CMS also publishes current diagnosis code files and coding guidelines.

Are ICD-10 and CPT codes the same?

No. ICD-10-CM codes report diagnoses and reasons for healthcare encounters. CPT codes describe medical procedures and professional services. Both may appear on the same healthcare claim.

Can an incorrect ICD-10 code cause a claim denial?

Yes. Invalid codes, unsupported diagnoses, incorrect sequencing, and inappropriate diagnosis-to-procedure relationships can contribute to rejection or denial. The specific outcome depends on the error and payer requirements.

Does ICD mean a defibrillator?

ICD has more than one meaning in healthcare. In medical coding, ICD means International Classification of Diseases. In cardiology, ICD may refer to an implantable cardioverter-defibrillator. The two uses should not be confused when performing diagnosis-code searches.

How often are ICD-10-CM codes updated?

ICD-10-CM is updated through official U.S. releases, generally aligned with the federal fiscal year beginning October 1. Additional updates may occur, so practices should confirm the release applicable to the date of service.

Conclusion

Accurate ICD-10-CM coding starts with understanding the medical record, not searching for a code that appears to match a few words.

The Alphabetic Index helps identify possible codes, while the Tabular List establishes the instructions needed to validate them. Coding conventions, diagnosis sequencing, documentation specificity, and code-set effective dates all influence the final selection.

For healthcare providers, these details matter because incorrect diagnosis coding can interrupt claims processing, create compliance concerns, and contribute to reimbursement delays.

Practices that consistently review official coding instructions, maintain updated references, and connect clinical documentation with claim requirements are better positioned to reduce preventable billing errors.

Need help with ICD-10-CM coding accuracy and medical claims?

Professional medical coding and billing support can help your practice review diagnosis coding, identify recurring claim errors, and maintain processes aligned with applicable payer requirements.

Request a Free Medical Billing Assessment to identify opportunities for improving coding accuracy and claim submission quality.

Coding note: All ICD-10-CM examples should be evaluated against the official code set, documentation, coding guidelines, and applicable payer requirements for the specific date of service.