Change in Adult Reference Range for Free Thyroxine (Free T4) Assay

Beginning February 23, 2016, the University of Iowa Hospitals and Clinics (UIHC) core clinical laboratory will change the adult (18+ years old) reference range for free thyroxine (T4):

Test Epic # Previous range New Range
THYROXINE – FREE (FREE T4) LAB127 0.90 – 1.70 ng/dL 0.80 – 1.80 ng/dL

Reference ranges for free T4 for pediatric patients (less than 18 years old) are not changing.

Questions should be directed to Matthew Krasowski, MD, PhD, medical director of the Clinical Chemistry (384-9380,