Chapter 17 — Congenital Malformations, Deformations and Chromosomal Abnormalities
Congenital anomalies may be principal or secondary, may be diagnosed at any age, and are coded throughout life — with additional codes only for manifestations that are not inherent.
Congenital anomaly codes may be principal or secondary, may be assigned at any age, and are assigned whenever the condition is diagnosed — not only when it is diagnosed at birth. The one judgement call in the chapter is which manifestations are inherent to the anomaly and which are not.
Chapter 17 in full#
| Rule | Detail |
|---|---|
| When to assign | Assign an appropriate code from Q00–QA1 when a malformation, deformation, chromosomal abnormality or genetic disorder is documented |
| Sequencing | The anomaly may be the principal / first-listed diagnosis or a secondary diagnosis on a record |
| No unique code | Where the malformation, deformation, chromosomal abnormality or genetic disorder does not have a unique code assignment, assign additional code(s) for any manifestations that may be present |
| Unique code exists | NEVER Where the code specifically identifies the anomaly, manifestations that are an inherent component of the anomaly are not coded separately. ALWAYS Additional codes are assigned for manifestations that are not an inherent component |
| Throughout life | Chapter 17 codes may be used throughout the life of the patient |
| Corrected anomaly | Where a congenital malformation or deformity has been corrected, a personal history code is used to identify the history of the malformation or deformity |
| Diagnosed later in life | Although present at birth, a malformation, deformation, chromosomal abnormality or genetic disorder may not be identified until later in life. Whenever the condition is diagnosed by the provider, it is appropriate to assign a code from Q00–QA1 |
| Birth admission | The appropriate code from category Z38 is sequenced as the principal diagnosis, followed by any congenital anomaly codes in Q00–QA1 |
Practice questions#
Q1A congenital anomaly is first diagnosed in a 46-year-old patient. May a code from Q00-QA1 be assigned?
- ANo — congenital codes are limited to the perinatal period
- BYes — whenever the condition is diagnosed by the provider
- COnly with a personal history code
- DOnly if the patient was diagnosed before age 18
Show answer & rationale
Correct answer: B. Yes — whenever the condition is diagnosed by the provider
Rationale. Section I.C.17 states that codes from Chapter 17 may be used throughout the life of the patient, and that although present at birth a malformation, deformation, chromosomal abnormality or genetic disorder may not be identified until later in life — whenever the condition is diagnosed by the provider, it is appropriate to assign a code from categories Q00-QA1.
Q2A chromosomal abnormality has a unique code that specifically identifies it. One of the patient's documented findings is an inherent component of that abnormality. What is assigned?
- ABoth the abnormality code and a code for the inherent manifestation
- BThe abnormality code only
- CA code for the manifestation only
- DThe abnormality code plus a personal history code
Show answer & rationale
Correct answer: B. The abnormality code only
Rationale. Section I.C.17 states that when the code assignment specifically identifies the malformation, deformation, chromosomal abnormality or genetic disorder, manifestations that are an inherent component of the anomaly should not be coded separately, and that additional codes should be assigned for manifestations that are not an inherent component.
Q3A newborn is delivered in hospital and a congenital cardiac anomaly is diagnosed during the birth admission. What is the principal diagnosis?
- AThe congenital anomaly code
- BA code from category
Z38 - CA code from Chapter 16
- DA code from
Z05
Show answer & rationale
Correct answer: B. A code from category Z38
Rationale. Section I.C.17 states that for the birth admission the appropriate code from category Z38, liveborn infants according to place of birth and type of delivery, should be sequenced as the principal diagnosis, followed by any congenital anomaly codes in categories Q00-QA1. Section I.C.16.a.2 gives the same rule from the perinatal chapter's side.
Q4A congenital malformation was surgically corrected in childhood and no longer exists. The patient is now an adult. What is used?
- AThe congenital anomaly code
- BA personal history code
- CA status code from
Z98 - DNo code at all
Show answer & rationale
Correct answer: B. A personal history code
Rationale. Section I.C.17 states that if a congenital malformation or deformity has been corrected, a personal history code should be used to identify the history of the malformation or deformity. Section I.C.21.c.4 explains the general principle: personal history codes explain a past medical condition that no longer exists and is not receiving treatment, but that has the potential for recurrence and may require continued monitoring.
Q5A genetic disorder is documented but has no unique code assignment in the classification. What is assigned?
- AAn unspecified congenital anomaly code only
- BAdditional codes for any manifestations that are present
- CNo code
- DA symptom code only
Show answer & rationale
Correct answer: B. Additional codes for any manifestations that are present
Rationale. Section I.C.17 states that when a malformation, deformation, chromosomal abnormality or genetic disorder does not have a unique code assignment, additional codes should be assigned for any manifestations that may be present. Section I.B.15 gives the parallel rule for syndromes: follow the Alphabetic Index guidance, and in its absence assign codes for the documented manifestations.
Scenarios#
A child with a documented genetic syndrome has a cardiac defect that is a defining feature of the syndrome, and separately has a fracture of the left radius sustained in a fall at school.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | Q-code | the specific code for the genetic syndrome |
| 2 | S52.- | the fracture code with the appropriate 7th character |
| 3 | External cause | the applicable Chapter 20 codes for the fall, place, activity and status |
Rationale. Section I.C.17 excludes manifestations that are an inherent component of the anomaly from separate coding where the code specifically identifies the anomaly, and requires additional codes for manifestations that are not inherent. The fracture is not a manifestation of the syndrome at all; it is a current acute injury coded from Chapter 19 under Section I.C.13.b, with external cause codes under Section I.C.20. Section I.B.15 would govern if the Alphabetic Index offered specific guidance for the syndrome.
Guideline: Section I.C.17, I.B.15, I.C.13.b
An inpatient record for an adult carries a congenital anomaly code from category Q21. The coder must complete the POA indicator field.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | Q21.- | the congenital anomaly code — POA field left blank, because categories Q00-Q99 are on the exempt list |
Rationale. Appendix I directs assignment of Y for congenital conditions and anomalies, because congenital conditions are always considered present on admission — except for categories Q00-Q99, which are on the exempt list. Appendix I also states that leaving the POA field blank is the only circumstance in which the field may be left blank, and points to the CDC website for the detailed list of codes exempt from POA reporting.
Guideline: Appendix I
Primary sources#
- ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027CMS — the source document for every page on this site (effective 1 Oct 2026)
- NCHS ICD-10-CM files — Tabular List, Index, POA exempt listOfficial code files, addenda and the list of codes exempt from POA reporting
- ICD-10 Coordination and Maintenance CommitteeWhere code proposals are debated; agendas, summaries and meeting materials
- CMS ICD-10 homeCode sets, transition guidance and Medicare coding policy
- AHA Coding ClinicOfficial coding advice from the AHA Central Office — subscription required
- HHS OIG Work PlanActive audit topics — useful for prioritising internal coding audits
- MEDESUN Medical Coding AcademyTraining, credential preparation and audit services by the author