ICD-10-CM > S00-T88 > T36-T50 > T38 > T38.1 > T38.1X > T38.1X6 T38.1X6 Underdosing of thyroid hormones and substitutes Non-Billable/Non-Specific Codes T38.1X6A..., initial encounterT38.1X6D..., subsequent encounterT38.1X6S..., sequela