Why and How to Learn the ICD-10-CM Coding Guidelines

** This article was reviewed and updated on December 7, 2023. **

Have you ever asked yourself, “Why do I need to know the ICD-10-CM coding guidelines to code medical records? Or “How do I learn them all?” These are questions often asked by new medical coding students.

In this article, I will explain the Official Coding Guidelines and why and how to learn them. In addition, I will provide some of the coding guidelines along with coding examples to show you the importance of knowing these guidelines and how you can apply them in your everyday coding.  

What Are the ICD-10-CM Official Guidelines for Coding and Reporting?

The ICD-10-CM Official Guidelines for Coding and Reporting are a set of rules to supplement the official conventions and instructions provided within the ICD-10-CM. Conventions and instructions of the classification take precedence over the guidelines. 

The United States published the ICD-10-CM, a morbidity classification, for classifying diagnoses and the reason for visits in all healthcare settings. It is based on the World Health Organization’s (WHO’s) ICD-10, the statistical classification of disease.

The ICD-10-CM guidelines are based on the coding and sequencing instructions in the Tabular List and Alphabetic Index of ICD-10-CM but provide additional instruction. The Health Insurance Portability and Accountability Act (HIPAA) requires that these guidelines be followed for all healthcare settings. 

Purpose of the ICD-10-CM Coding Guidelines and Why We Need to Learn Them

The guidelines were put in place to help the healthcare provider and medical coder identify those diagnoses that need to be reported and in what order. Everyone must follow the same rules to ensure consistent and complete documentation. Anything less than that results in inaccurate coding. 

Accurate diagnosis coding ensures proper reimbursement, quality data monitoring for outcomes, and more specific data for research purposes.  

Inaccurate coding can also affect a patient’s treatment and potentially lead to charges of fraud or abuse.

Who Developed and Approved the ICD-10-CM Official Guidelines for Coding and Reporting?

The Centers for Medicare & Medicaid Services (CMS) and the National Center for Health Statistics (NCHS) developed the coding guidelines. 

The four organizations that make up the cooperating parties that approved the ICD-10-CM Official Guidelines for Coding and Reporting are:

• Centers for Medicare and Medicaid Services (CMS)
• National Center for Health Statistics (NCHS)  
• American Hospital Association (AHA)
• American Health Information Management Association (AHIMA)

Where Are the Coding Guidelines Located, and How Are They Organized?

The guidelines are located in the front of the ICD-10-CM code book and are organized into four sections. They are: 

• Section I. Conventions, General Coding Guidelines, and Chapter-Specific Guidelines
  • Structure and conventions of ICD-10-CM, general guidelines, and chapter-specific guidelines  
• Section II. Selection of Principal Diagnosis
  • Selection of principal diagnosis for non-outpatient settings (acute care, short-term care, long-term care, psychiatric hospitals, home health agencies, rehab facilities, nursing homes, etc.)
• Section III. Reporting Additional Diagnoses
  • Additional diagnoses that affect patient care in non-outpatient settings.
• Section IV. Diagnostic Coding and Reporting Guidelines for Outpatient Services
  • Outpatient coding and reporting. Guidelines for Outpatient diagnoses have been approved for use by hospitals and providers in coding and reporting hospital-based outpatient services and provider-based office visits.  

You can also get a copy of the current coding guidelines from the Centers for Medicare & Medicaid Services. 

How to Learn the ICD-10-CM Coding Guidelines

The only way to learn the coding guidelines is to read them and apply them repeatedly. There are no shortcuts. Without knowing the coding guidelines, it’s impossible to code accurately. You will learn them as you use them in your everyday coding. Either read the guidelines in your code book or download a copy from the CMS website and print them out. You may wish to read a section at a time or several pages, but try to set aside time each day for this task. 

Flashcards can also be helpful in learning specific guidelines. 

---

A supplement to your coding textbooks is also available for students and for those already working in the field who need a quick reference to the coding guidelines.

---

Do You Need to Memorize the Coding Guidelines?

No, it is impossible to memorize all the guidelines, just like it’s impossible to memorize all the ICD-10-cm codes. You will find that you will remember many of the coding guidelines as you consistently assign them.  

What Are Some of the Specific Guidelines in ICD-10-CM? 

There are far too many coding guidelines to discuss them all here. However, I will provide a few guidelines from each section and explain how the guideline is applied in a given example. You may wish to follow along in your coding manual. 

While reading the guidelines and examples, think about how you would code the examples without knowing the coding guidelines. It would be difficult to code consistently and accurately without them.

Section I. Conventions, general coding guidelines, and chapter-specific guidelines.

Section I is the most extensive section with the most coding guidelines. It is divided into three subsections:

• A. Conventions
• B. General Coding Guidelines
• C. Chapter-Specific Coding Guidelines  

The following is a coding guideline from each subsection and a coding example.

A. Conventions for the ICD-10-CM

Section I.A.2. Format and Structure

Coding guidelines state,

“The ICD-10-CM Tabular List contains categories, subcategories, and codes. Characters for categories, subcategories, and codes may be letters or numbers. All categories are 3 characters. A three-character category that has no further subdivision is equivalent to a code. Subcategories are either 4 or 5 characters. Codes may be 3, 4, 5, 6, or 7 characters. That is, each level of subdivision after a category is a subcategory. The final level of subdivision is a code. Codes that have applicable 7th characters are still referred to as codes, not subcategories. A code that has an applicable 7th character is considered invalid without the 7th character. “

“The ICD-10-CM uses an indented format for ease in reference.”

EXAMPLES

1. B20 (Human immunodeficiency virus [HIV] disease) is a three-character category with no further subdivisions and is equivalent to a code.
2. J02 (Acute pharyngitis) is a three-character category.
   J02.0 (Streptococcal pharyngitis) is a subcategory of category J02. There is no further subdivision of J02.0, which makes J02.0 a code.
3. F43 (Reaction to severe stress and adjustment disorders) is a three-character category code.
   F43.2 (Adjustment disorders) is a subcategory of category F43.
   F43.21 (Adjustment disorder with depressed mood) is a subcategory of F43.2. There is no further subdivision, making F43.21 a code. 
4. T38 (Poisoning by, adverse effect of, and underdosing of hormones and their substitutes and antagonists, not elsewhere classified) is a three-character category.
5. T38.0 (Poisoning by, adverse effect of, and underdosing of glucocorticoids and synthetic analogues) is a subcategory of category T38.
6. T38.0X1 (Poisoning by glucocorticoids and synthetic analogues, accidental (unintentional) is an invalid code and requires a 7th character based on the episode of care.
7. T38.0X1D (Poisoning by glucocorticoids and synthetic analogues, accidental (unintentional), subsequent encounter) is a valid code with the 7th character “D” to show the patient is receiving routine care for the injury during the healing or recovery phase.

B. General Coding Guidelines

Section I.B.5. Conditions that are an integral part of a disease process 

Coding guidelines state,

“Signs and symptoms that are associated routinely with a disease process should not be assigned as additional codes unless otherwise instructed by the classification.”

EXAMPLE

The physician documents convulsions and seizures due to epilepsy. 

Answer: G40.909

Convulsions and seizures are integral to epilepsy, so the coder should only assign a code for epilepsy. Codes for convulsions and seizures should not be assigned as additional codes. 

Locate and Verify

When we look up Epilepsy in the Alphabetic Index, we see Epilepsy, epileptic, epilepsia (attack) (cerebral) (convulsion) (fit) (seizure) G40.909. 

In the Tabular, we can verify the correct code as:

G40.909, Epilepsy, unspecified, not intractable, without status epilepticus

Inclusion terms:
Epilepsy NOS
Epileptic convulsions NOS
Epileptic fits NOS
Epileptic seizures NOS
Recurrent seizures NOS
Seizure disorder NOS

The classification does not tell us to code for convulsions and seizures. 

Section I.B.6. Conditions that are not an integral part of a disease process 

Coding guidelines state,

“Additional signs and symptoms that may not be associated routinely with a disease process should be coded when present.”

EXAMPLE

The physician documents polyuria, dysuria, hematuria, and skin rash. A urinalysis is positive for UTI. The physician performs a skin biopsy and orders a blood test to determine the cause of the rash.

Answer: N39.0, R21

Polyuria (excessive production of urine), dysuria (painful urination), and hematuria (blood in the urine) are integral to UTI (urinary tract infection). The physician confirmed the UTI with a urinalysis. A skin rash is not associated routinely with a UTI; therefore, it needs to be coded in addition to the UTI.   

Locate and Verify 

Look in the Alphabetic Index under Infection, infected, infective (opportunistic)/urinary (tract) N39.0. In the Tabular, we can verify our correct code as:

N39.0, Urinary tract infection, site not specified

Look in the Index under Rash (toxic) R21. In the Tabular, we can verify our correct code as:

R21, Rash and other nonspecific skin eruption

Inclusion term: Rash NOS

C. Chapter-Specific Coding Guidelines 

I.C.2. Chapter 2: Neoplasms (C00-D49) 

The following guidelines for FY 2024 include narrative changes in bold text. Italics are used to indicate revisions to heading changes. There is also an example below for each part of the guideline.

Section I.C.2.a. Admission/encounter for treatment of primary site

“If the malignancy is chiefly responsible for occasioning the patient admission/encounter and treatment is directed at the primary site, designate the primary malignancy as the principal/first-listed diagnosis.” (See Example #1 below)

“The only exception to this guideline is if the administration of chemotherapy, immunotherapy, or external beam radiation therapy is chiefly responsible for occasioning the admission/encounter. In that case, assign the appropriate Z51.– code as the first-listed or principal diagnosis, and the underlying diagnosis or problem for which the service is being performed as a secondary diagnosis.” (See Example #2 below)

EXAMPLE #1

A female patient previously diagnosed with carcinoma of the lower-inner quadrant left breast is now diagnosed with axillary lymph node metastasis. Treatment is focused on the primary malignancy.   

Answer: C50.312, C77.3

The patient encounter was for treating the primary site, carcinoma of the lower-inner quadrant of the left breast, on a female. The primary malignancy should be sequenced first, followed by the secondary malignancy of the axillary lymph node.  

Locate and Verify

To find these codes, go to the Table of Neoplasms under breast (connective tissue) (glandular tissue) (soft parts); lower-inner quadrant – Malignant primary C50.3-.

In the Tabular List, we can verify our correct code as: 

C50.312, Malignant neoplasm of lower-inner quadrant of left female breast

In the Neoplasm Table, look up lymph, lymphatic, channel NEC, gland (secondary); axilla, axillary – Malignant Secondary C77.3.

In the Tabular, our correct code is:

C77.3, Secondary and unspecified malignant neoplasm of axilla and upper limb lymph nodes

Inclusion term: Secondary and unspecified malignant neoplasm of pectoral lymph nodes

EXAMPLE #2

A patient with a neoplasm of the right ovary is seen today for chemotherapy. 

Answer: Z51.11, C56.1

The reason for the encounter is chemotherapy. The code for chemotherapy (Z51.-) should be assigned as the first-listed or principal diagnosis. The underlying diagnosis for which the service is being performed is a neoplasm of the right ovary. This should be reported as a secondary diagnosis.

Locate and Verify

Look up Chemotherapy (session) (for)/neoplasm Z51.11 in the Alphabetic Index. 

In the Tabular, we can verify our correct code as:

Z51.11, Encounter for antineoplastic chemotherapy

Category Z51 includes a note to “Code also” the condition requiring care. The condition requiring care is the neoplasm of the ovary. Look in the Neoplasm Table under ovary Malignant Primary C56-. 

In the Tabular, we can verify our correct code as:

C56.1, Malignant neoplasm of right ovary

Section II. SELECTION OF PRINCIPAL DIAGNOSIS 

II.J. Admission from Outpatient Surgery 

The coding guidelines state,

“When a patient receives surgery in the hospital’s outpatient surgery department and is subsequently admitted for continuing inpatient care at the same hospital, the following guidelines should be followed in selecting the principal diagnosis for the inpatient admission:

• If the reason for the inpatient admission is a complication, assign the complication as the principal diagnosis.
• If no complication, or other condition, is documented as the reason for the inpatient admission, assign the reason for the outpatient surgery as the principal diagnosis.
• If the reason for the inpatient admission is another condition unrelated to the surgery, assign the unrelated condition as the principal diagnosis.”

EXAMPLE

A female patient presents to the hospital outpatient surgery department for laparoscopic cholecystectomy for cholelithiasis, cholecystitis, and large gallbladder polyps. While in the recovery room, the patient began developing palpitations, chest pain, and shortness of breath. The patient has a history of chronic atrial fibrillation and was admitted as an inpatient. Assign for the principal diagnosis.

Answer: I48.20

A laparoscopic cholecystectomy was performed to remove the patient’s diseased gallbladder. According to the Mayo Clinic, the procedure is most commonly performed when a patient has:

• Cholelithiasis (gallstones in the gallbladder)
• Choledocholithiasis (gallstones in the bile duct)
• Large gallbladder polyps
• Pancreatitis (pancreas inflammation) due to gallstones

The inpatient admission is due to chronic atrial fibrillation, another condition unrelated to laparoscopic surgery. That means chronic atrial fibrillation is our principal diagnosis for inpatient admission. There is no need to code for palpitations, chest pain, and shortness of breath because a related definitive diagnosis of atrial fibrillation has been established.

Symptoms of atrial fibrillation, when they occur, may include the following, according to the Centers for Disease Control and Prevention (CDC):

• Irregular heartbeat
• Heart palpitations (rapid, fluttering, or pounding)
• Lightheadedness
• Extreme fatigue
• Shortness of breath
• Chest pain

Atrial fibrillation is often called AFib or AF. AFib is the most common type of heart arrhythmia (irregular heartbeat).

Locate and Verify

In the Alphabetic Index, look up Fibrillation/atrial or auricular (established)/chronic I48.20. 

In the Tabular, we can verify our correct code as:

I48.20, Chronic atrial fibrillation, unspecified

Section III. Reporting Additional Diagnoses

III.C. Uncertain Diagnosis

Coding guidelines state,

“If the diagnosis documented at the time of discharge is qualified as “probable,” “suspected,” “likely,” “questionable,” “possible,” or “still to be ruled out,” “compatible with,” “consistent with,” or other similar terms indicating uncertainty, code the condition as if it existed or was established. The bases for these guidelines are the diagnostic workup, arrangements for further workup or observation, and initial therapeutic approach that correspond most closely with the established diagnosis.”

“Note: This guideline applies only to inpatient admissions to short-term, acute, long-term care, and psychiatric hospitals.”

EXAMPLE

The documentation upon hospital discharge states the patient’s diagnosis is consistent with polyneuropathy from excessive alcohol use.

Answer: G62.1

The Merck Manual specifies that one of the known causes of polyneuropathy is excessive use of alcohol. Polyneuropathy is a simultaneous malfunction of many peripheral nerves throughout the body.

The coding guidelines state that if “consistent with” is used in the documentation, the coder should code the condition as if it existed at the time of discharge. This guideline is only for inpatient admissions to short-term, acute, long-term care, and psychiatric hospitals. It does not apply to outpatient coding.

Locate and Verify

In the Alphabetic Index, look up Polyneuropathy (peripheral)/alcoholic G62.1.

In the Tabular, we can verify our correct code as:

G62.1, Alcoholic polyneuropathy

Section IV. Diagnostic Coding and Reporting Guidelines for
Outpatient Services

IV. I. Chronic diseases

Coding guidelines state,

“Chronic diseases treated on an ongoing basis may be coded and reported as many times as the patient receives treatment and care for the condition(s).”

EXAMPLE

An established patient is seen for continued management of type 2 diabetes and hypertension.

Answer: E11.9, I10

Locate and Verify – Diabetes

In the Alphabetic Index, look up Diabetes, diabetic (mellitus) (sugar)/type 2 E11.9.

In the Tabular, we can verify our correct code as:

E11.9, Type 2 diabetes mellitus without complications

Locate and Verify – Hypertension

In the Alphabetic Index, look up Hypertension, hypertensive (accelerated) (benign) (essential) (idiopathic) (malignant) (systemic) I10.

In the Tabular, we can verify our correct code as:

I10, Essential (primary) hypertension

Conclusion

Providers and medical coders rely on the ICD-10-CM coding guidelines to ensure that the documentation is complete and consistent and that diagnosis codes are assigned and sequenced correctly. This can only be done by reading and understanding the guidelines and using them daily in coding. Hopefully, the guidelines and examples in this article have enhanced your knowledge and clarified why and how learning these guidelines is essential to accurate coding.

---

Related

• Medical Coding Business of Medicine
• Clear the Decks for 395 New ICD-10-CM Codes (FY 2024)
• Tropin’s “ICD-10-CM Coding Guidelines Made Easy” Book Review
• 3 Reasons to Know Medical Terminology and Optimal Learning Strategies
• What are ICD-10-CM, ICD-10-PCS, CPT, and HCPCS?