The Body System None is identified by letter "Z" and occupies the 4th position in the ICD10-PCS procedure code structure.
Below a selection of ICD 10 PCS codes related to 4A0Z
Measurement of Metabolism, External Approach
Measurement of Metabolism, Via Natural or Artificial Opening
Measurement of Sleep, External Approach
Measurement of Temperature, Via Opening
Measurement of Temperature, External Approach