Down Syndrome: ICD-10-CM Coding

Down Syndrome: ICD-10-CM Coding

Down syndrome is a genetic condition in which a person is born with an extra copy of chromosome 21 (normally, individuals have 23 pairs of chromosomes in each cell); thus, the name “trisomy 21.” This condition, nondisjunction, is an error in cell division that occurs at conception. Down syndrome is the most common chromosomal abnormality.
Individuals with Down syndrome may have delayed mental and social development, congenital heart defects, dementia, vision problems, gastrointestinal problems, hearing problems, sleep disturbance, and hypothyroidism. The number and severity of the conditions will vary from patient to patient.
There are three, specific varieties of Down syndrome:
1. Nonmosaic Trisomy 21, also called meiotic nondisjunction, results in an extra chromosome in every cell of the body. This is the most common form of Down syndrome, occurring in most patients with the condition (more than 90 percent of the time).
2. Mosaic Trisomy 21, also defined as mitotic nondisjunction, results in an extra chromosome in some cells, while others cells are normal.
3. Translocation Trisomy 21 means that part of chromosome 21 is attached (translocated) onto another chromosome, either before or after conception. This results in the usual two pairs of chromosome 21, but there is also additional material from chromosome 21 attached to the translocated chromosome. This is the only type of Down syndrome that can be inherited.

Documentation and Code Selection

Good clinical documentation should indicate the type of Down syndrome (nonmosaic, mosaic, or translocation), any associated physical conditions, and the degree of intellectual diabailities:

Q90.0 Trisomy 21, nonmosaicism (meiotic nondisjunction)
Q90.1 Trisomy 21, mosaicism (mitotic nondisjunction)
Q90.2 Trisomy 21, translocation
Q90.9 Down syndrome, unspecified

An instructional note under category Q90 instructs you to use an additional code(s) to identify any associated physical conditions, and degree of intellectual disabilities (F70-F79).
Example: A 6-week-old male infant has been transferred to Children’s Hospital because of his nonmosaic down syndrome and congenital heart disease. He has not been able to feed well and has to be feed by a NG tube. His swallowing mechanism does not appear to be very functional. To aid in her home care, it is felt she would be better served with a gastrostomy.
Code selection: Q90.0
Example: Noah is a newborn who presents with his parents today for evaluation. He has upward slanting eyes, a flat face, and a large space between the big toe and second toe. After examination the physician diagnoses the baby with Down syndrome. The provider orders a karyotype test.
Code selection: Report Q90.9 because documentation does not indicate the type of trisomy.

John Verhovshek
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John Verhovshek, MA, CPC, is a contributing editor at AAPC. He has been covering medical coding and billing, healthcare policy, and the business of medicine since 1999. He is an alumnus of York College of Pennsylvania and Clemson University.

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