Final answer:
Diagnosis codes are reported at their highest number of characters available, which is usually three to seven characters.
Step-by-step explanation:
The statement 'Diagnosis codes are reported at their highest number of characters available' is True. The highest number of characters available for diagnosis codes is usually three to seven characters, depending on the coding system used, such as ICD-10-CM or CPT. The codes are reported at their highest level of specificity to accurately describe the patient's condition or procedure.