Down Syndrome ICD-10-CM codes

Category Q90 has four codes: Q90.0 trisomy 21, nonmosaicism (meiotic nondisjunction), Q90.1 trisomy 21, mosaicism (mitotic nondisjunction), Q90.2 trisomy 21, translocation, and Q90.9 Down syndrome, unspecified. Assign Q90.0, Q90.1, or Q90.2 only when the karyotype or provider documentation states the mechanism; Q90.9 is correct when the record simply says Down syndrome.

Congenital anomaly codes are used at any age, so Q90 is reported on adult encounters whenever the condition affects care. Associated conditions are coded separately: a complete atrioventricular septal defect is Q21.23, a ventricular septal defect is Q21.0, and intellectual disability is F70 to F79 (F79 when the degree is unspecified) only when the provider documents it. Do not assume intellectual disability from the diagnosis of Down syndrome.

On the birth admission Z38 (for example Z38.00) is the principal diagnosis and Q90 is secondary. A prenatal encounter for a fetus with suspected or confirmed trisomy 21 is coded on the maternal record with an O35 code, not with Q90.