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ICD-10-CM 2027

ICD-10 code for chromosome s additional

Q99.8

Other specified chromosome abnormalities

Header — needs a more specific code

From the official ICD-10-CM alphabetic index entry “Additional › chromosome (s)”. Page updated September 29, 2026.

About coding chromosome s additional

The ICD-10-CM code for chromosome s additional is Q99.8 (Other specified chromosome abnormalities).

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).

More specific chromosome s additional codes (official index)

  • marker
  • sex
  • 21

Common questions about chromosome s additional ICD-10 codes

What is the ICD-10 code for chromosome s additional?

Q99.8 — Other specified chromosome abnormalities (a header code; report a more specific subcode).

Is Q99.8 billable?

No. Q99.8 is a header code. Report one of its more specific subcodes instead.