Trisomy 18 and Trisomy 13 (Q91)

ICD-10 codes Q91 cover genetic chromosomal abnormalities known as Trisomy 18 and Trisomy 13, including their various forms such as nonmosaicism, mosaicism, and translocation types. These codes are used specifically to identify and classify different presentations of these serious congenital conditions.

The code Q91 and its subcategories relate to Trisomy 18; also called Edward’s syndrome; and Trisomy 13, known as Patau’s syndrome. These syndromes occur when an individual has an extra copy of chromosome 18 or 13, respectively. The set includes distinctions such as Q91.0 and Q91.4, identifying nonmosaicism cases due to meiotic nondisjunction (complete extra chromosome), and Q91.1 and Q91.5 for mosaicism from mitotic nondisjunction, where only some cells have the extra chromosome. Translocation forms, coded as Q91.2 and Q91.6, indicate partial trisomies caused by chromosome rearrangement. Unspecified cases fall under Q91.3 and Q91.7. Recognizing these synonyms and variants, such as "Complete trisomy 18 syndrome" or "Partial trisomy 13 in Patau's syndrome," helps medical coders accurately assign the correct ICD-10 code based on precise clinical and genetic findings. This section is essential for diagnosing, documenting, and billing genetic testing and related healthcare services for these complex chromosomal disorders.