What is the function of square brackets in ICD-10-CM codes?

In ICD-10-CM coding, square brackets are used to denote non-essential modifiers. This means that the terms contained within the square brackets provide additional information that can help clarify the condition being coded, but they are not necessary for the understanding or application of the code itself.

For instance, if a code includes a term in square brackets, it is indicating that this term may be used to further specify the condition if applicable, but it does not change the meaning or requirements of the base code. This allows for greater specificity and detail in the coding process without imposing restrictions on the primary code.

The use of square brackets helps coders to identify supplementary terms that enhance understanding of the diagnosis while maintaining the flexibility to use the codes accurately without these modifiers.