ICD-10-CM has 22 chapters. Chapters 1 through 21 run from A00 (infectious diseases) through Z99 (factors influencing health status), while Chapter 22 holds the U00 through U85 codes for special purposes. In addition, each chapter has its own section of the Official Guidelines, and knowing which chapter a condition lives in is one of the fastest ways to move through the CPC exam.
ICD-10-CM Chapters: What’s Included, Guidance, and Coding Tips
The medical coding ICD-10-CM chapters manual is organized into 22 chapters, each covering a specific range of codes tied to body systems, conditions, or circumstances. Therefore, understanding what belongs in each chapter, and the rules that apply, helps coders assign the most accurate codes, pass certification exams, and avoid denials.
Chapter 1: A00–B99 – Certain Infectious and Parasitic Diseases
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Includes: Bacterial, viral, parasitic, protozoal, helminthic infections; sepsis; HIV; TB; Zika; COVID-19.
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Guidance: Many codes here require additional coding for the organism (e.g., bacterial agent) or manifestations (e.g., pneumonia due to influenza).
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Tip: Always check if the condition requires a combination code (like HIV with related illness) vs. multiple codes.
Chapter 2: C00–D49 – Neoplasms
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Includes: Malignant, benign, in situ, and uncertain behavior tumors.
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Guidance: Use the Neoplasm Table in the Alphabetic Index; pay attention to primary vs. secondary (metastatic) sites.
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Tip: Usually code the primary site first, then the secondary. However, when treatment is directed only at the secondary site, sequence the secondary site first. Use “history of” codes (Z85–) when cancer is resolved but documented as history.
Chapter 3: D50–D89 – Diseases of the Blood and Blood-Forming Organs, and Certain Disorders of the Immune Mechanism
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Includes: Anemias, coagulation defects, hemophilia, and immune deficiencies. Leukemias are neoplasms, so you code them in Chapter 2.
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Guidance: Look for causative factors (iron deficiency, chronic disease, anemia).
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Tip: Link anemia to underlying conditions whenever possible.
Chapter 4: E00–E89 – Endocrine, Nutritional, and Metabolic Diseases
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Includes: Diabetes, thyroid disorders, malnutrition, metabolic disorders.
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Guidance: Diabetes codes (E08 through E13) require specificity: the type, the cause, any complications, and whether hyperglycemia or hypoglycemia is documented.
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Tip: Always confirm Type 1 vs. Type 2 diabetes and whether complications are present.
Chapter 5: F01–F99 – Mental, Behavioral, and Neurodevelopmental Disorders
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Includes: Depression, schizophrenia, dementia, anxiety, and substance-related disorders.
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Guidance: Mental health coding requires documentation of type, severity, and recurrence.
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Tip: For substance abuse, differentiate between use, abuse, and dependence.
Chapter 6: G00–G99 – Diseases of the Nervous System
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Includes: Epilepsy, migraines, multiple sclerosis, Parkinson’s disease.
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Guidance: Pay attention to laterality (left vs. right) for neurologic conditions.
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Tip: Many neurological conditions require secondary coding for associated symptoms (e.g., seizures).
Chapter 7: H00–H59 – Diseases of the Eye and Adnexa
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Includes: Glaucoma, cataracts, retinal disorders, and conjunctivitis.
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Guidance: Laterality (right, left, bilateral) is critical.
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Tip: For glaucoma, identify the type and stage.
Chapter 8: H60–H95 – Diseases of the Ear and Mastoid Process
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Includes: Otitis media, hearing loss, vertigo, mastoiditis.
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Guidance: Similarly, laterality applies here, too.
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Tip: Acute vs. chronic otitis media coding is an exam favorite.
Chapter 9: I00–I99 – Diseases of the Circulatory System
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Includes: Hypertension, heart disease, stroke, and peripheral vascular disease.
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Guidance: Code hypertension with heart/kidney disease using combination codes.
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Tip: Sequence acute MI before history codes when coding encounters.
Chapter 10: J00–J99 – Diseases of the Respiratory System
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Includes: Pneumonia, asthma, COPD, and influenza.
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Guidance: Identify the causal organism for pneumonia; in addition, combination codes are common.
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Tip: For asthma, note if intermittent, persistent, or exacerbated.
Chapter 11: K00–K95 – Diseases of the Digestive System
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Includes: GERD, ulcers, Crohn’s, hernias, liver disease.
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Guidance: Differentiate Crohn’s vs. ulcerative colitis; cirrhosis requires cause coding (alcoholic, viral).
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Tip: Look for links to alcohol use or viral hepatitis.
Chapter 12: L00–L99 – Diseases of the Skin and Subcutaneous Tissue
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Includes: Dermatitis, cellulitis, psoriasis, and pressure ulcers. However, you code burns and corrosions in Chapter 19 (T20 through T32).
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Guidance: Pressure ulcers require the site and the stage.
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Tip: For pressure ulcers, code site + stage (always both).
Chapter 13: M00–M99 – Diseases of the Musculoskeletal System and Connective Tissue
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Includes: Arthritis, pathological and stress fractures, osteoporosis, and back pain. However, you code traumatic fractures in Chapter 19.
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Guidance: Pathological and stress fracture codes need a 7th character for the encounter: A initial, D subsequent with routine healing, G delayed healing, K nonunion, P malunion, and S sequela.
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Tip: Document laterality and episode of care.
Chapter 14: N00–N99 – Diseases of the Genitourinary System
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Includes: Kidney disease, urinary infections, prostate disorders, and infertility.
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Guidance: In particular, CKD stages (N18.1–N18.6) are critical.
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Tip: Link CKD with hypertension when documented.
Chapter 15: O00–O9A – Pregnancy, Childbirth, and the Puerperium
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Includes: Pregnancy complications, delivery, and postpartum issues.
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Guidance: Chapter 15 codes are used only on the mother’s record, never the newborn’s. You may add a Z3A weeks of gestation code for detail, but not for abortive outcomes, elective termination, or postpartum conditions.
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Tip: Use the O code first, then secondary condition codes.
Medical Coding Pregnancy and Childbirth
Chapter 16: P00–P96 – Certain Conditions Originating in the Perinatal Period
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Includes: Disorders in newborns (low birth weight, jaundice, birth injuries).
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Guidance: Used on the newborn’s record, and may be used throughout the patient’s life if the perinatal condition is still present.
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Tip: Differentiate birth injury vs. congenital anomaly.
Chapter 17: Q00–QA1 – Congenital Malformations, Deformations, Chromosomal Abnormalities, and Genetic Disorders
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Includes: Down syndrome, cleft palate, and congenital heart defects.
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Guidance: Code congenital anomalies as long-term conditions.
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Tip: Therefore, these remain coded even in adulthood.
Chapter 18: R00–R99 – Symptoms, Signs, and Abnormal Clinical and Laboratory Findings
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Includes: Chest pain, fever, abnormal labs, coma.
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Guidance: Only code symptoms when no definitive diagnosis is made.
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Tip: In inpatient coding, symptoms are rarely principal unless no diagnosis is confirmed.
Medical Coding Signs & Symptoms in Diseases and Medical Coding Labs
Chapter 19: S00–T88 – Injury, Poisoning, and Certain Other Consequences of External Causes
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Includes: Injuries, fractures, burns, poisonings, complications.
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Guidance: Use the 7th character to identify encounter type (initial, subsequent, sequela).
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Tip: Report external cause codes (Chapter 20) when a state mandate or payer requires them. There is no national requirement, but they are encouraged.
Medical Coding From the ICD-10-CM Table of Drugs And Chemicals
Chapter 20: V00–Y99 – External Causes of Morbidity
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Includes: Accidents, assaults, and environmental events.
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Guidance: Never used alone; instead, they explain how an injury occurred.
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Tip: Therefore, assign as secondary codes to injury/poisoning.
Chapter 21: Z00–Z99 – Factors Influencing Health Status and Contact with Health Services
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Includes: Encounters for screenings, immunizations, history, and follow-ups.
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Guidance: Use when the patient does not have a current illness but needs services.
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Tip: Common on exams (e.g., “encounter for colonoscopy screening”).
Chapter 22: U00 through U85, Codes for Special Purposes
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Includes: Codes the World Health Organization and CDC assign on a provisional basis for new diseases or emergency use.
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Guidance: U07.1 (COVID-19) and U09.9 (post COVID-19 condition) live in this range but follow the Chapter 1 guidelines.
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Tip: Chapter 22 was added after the original 21 chapters, which is why older study guides still say 21.
Final Tips for Coders
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Always use the Alphabetic Index first, then verify in the Tabular List.
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Watch for Excludes1/Excludes2 notes in each chapter because they prevent coding errors.
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Pay attention to laterality, specificity, and 7th characters.
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Sequence codes correctly (e.g., principal diagnosis first).
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Remember: Documentation drives coding—never assume.
FY2027 ICD-10-CM Official Guidelines
ICD-10-CM Chapters FAQs
How many chapters are in ICD-10-CM?
There are 22 chapters. Chapter 22, Codes for Special Purposes (U00 through U85), was added to the original 21.
What is the first chapter of ICD-10-CM?
Chapter 1, Certain Infectious and Parasitic Diseases, covers A00 through B99, along with U07.1 for COVID-19 and U09.9 for post COVID-19 condition.
Which chapter has the Z codes?
Chapter 21, Factors Influencing Health Status and Contact with Health Services (Z00 through Z99). In addition, Z codes explain screenings, history, status, aftercare, and follow up encounters. See our Z codes guide.
Are burns and traumatic fractures in the skin and musculoskeletal chapters?
No. Instead, burns, corrosions, and traumatic fractures are in Chapter 19 (S00 through T88). However, Chapter 13 covers pathological and stress fractures.
What changed in Chapter 17?
Chapter 17 now runs from Q00 through QA1 and includes genetic disorders, such as inherited cancer predisposition syndromes in category QA1.
Which ICD-10-CM chapters are tested most on the CPC exam?
Expect questions from across the code set. In particular, neoplasms, diabetes, circulatory, injury, and Z code guidelines show up often. Our CPC training walks through each chapter’s guidelines with practice cases.