Q99.8Other specified chromosome abnormalities

Q99.8 is the ICD-10-CM diagnosis code for other specified chromosome abnormalities. It belongs to category Q99 (other chromosome abnormalities, not elsewhere classified), block Q90-Q99 (chromosomal abnormalities, not elsewhere classified) and chapter 17 (congenital malformations, deformations, chromosomal abnormalities, and genetic disorders). It is a header code, so it can't be reported by itself; one of its 2 subcodes must be used instead.

Within Q99, choose Q99.8 (Other specified chromosome abnormalities) only when documentation doesn't support a more specific option: Chimera 46, XX/46, XY (Q99.0), 46, XX true hermaphrodite (Q99.1), fragile X chromosome (Q99.2) and chromosomal abnormality, unspecified (Q99.9).

To report this condition, pick the subcode that matches the documentation: Q99.81 (syndrome) and Q99.89 (abnormalities).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015, and changed in FY2026 (expanded into subcodes).

Before ICD-10, this condition was coded in ICD-9-CM as 758.81 (other conditions due to sex chromosome anomalies) and 758.89 (other conditions due to chromosome anomalies).