When coders are looking at scenarios in ICD-10-CM/PCS, where the X is located within the code matters.
When X is in the fifth and/or sixth character, X is a placeholder. ICD-10-CM codes can be up to seven characters long. However, not every code that requires a seventh character is actually seven characters long. So some codes do not have an applicable fifth digit. Some lack a fifth and a sixth character. In those cases, such as poisonings or injuries, coders will need to add a placeholder so the seventh character ends up in the correct position. Otherwise, the code will be invalid.
For example, a patient presents with an accidental poisoning by other anti-common-cold drugs. For the initial encounter, coders would report T48.5x1A. In this case the x is merely a placeholder so the sixth and seventh characters are in the correct position. If a coder inadvertently omits the placeholder, code T48.51A is not a valid code.
When X is at the beginning of the code, it indicates the chapter (i.e., codes X00–X99). For code category X78.0, the X is the category of codes and identifies intention of an injury, exposure, etc. The X series of codes is part of Chapter 20: External causes of morbidity.
The character X can be even more confusing to coders who work with both inpatient and outpatient records. In ICD-10-PCS, X can be used in multiple places, each with a different meaning. For example, in ICD-10-PCS code 0HB0XZX, the first X identifies that the approach was external and the second X identifies the procedure was diagnostic.