Is X99 a billable ICD-10-CM code?

No. X99 is a non-billable header code. Code to a higher level of specificity using one of its child codes.

Where does X99 sit in the tabular list?

External causes of morbidity (V00-Y99), in the block Assault (X92-Y09).

What cannot be coded together with X99?

X99 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.

X99

X99 — Assault by sharp object

Non-billable headerICD-10-CM

X99 is a non-billable header ICD-10-CM code for assault by sharp object. It cannot be billed on its own: choose one of the more specific child codes below. This code also requires a 7th character before it is complete.

This code requires a 7th character

The appropriate 7th character is to be added to each code from category X99

A: initial encounter
D: subsequent encounter
S: sequela

Excludes1 — never code together

These conditions cannot occur together. Billing both on the same encounter is a denial.

assault by strike by sports equipment (Y08.0-)

Other codes that can never be billed with X99

These codes carry an Excludes1 note pointing at X99. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading X99 alone.

Y04Assault by bodily force

Risk adjustment

X99 does not map to an HCC and does not risk-adjust under CMS-HCC V28. That is normal — most ICD-10 codes do not. It still needs to be coded correctly; it just will not move a RAF score.

Code to one of these instead X99

5 child codes. Green means billable.

Questions about X99

Is X99 a billable ICD-10-CM code?: No. X99 is a non-billable header code. Code to a higher level of specificity using one of its child codes.
Where does X99 sit in the tabular list?: External causes of morbidity (V00-Y99), in the block Assault (X92-Y09).
What cannot be coded together with X99?: X99 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.