192 - Free thyroxine and thyroid-stimulating hormone reference ranges in very preterm (VPT) and very low birth weight infants (VLBW) at one month of life
Saturday, April 29, 2023
3:30 PM – 6:00 PM ET
Poster Number: 192 Publication Number: 192.213
Bret Nolan, CHOC Children's Hospital of Orange County, ALHAMBRA, CA, United States; Fayez Bany-Mohammed, University of California, Irvine, School of Medicine, Orange, CA, United States; Cherry Uy, University of California, Irvine, School of Medicine, Orange, CA, United States; Lisa Stablein, UC Irvine Medical center, Orange, CA, United States
Neonatologist CHOC Children's Hospital of Orange County ALHAMBRA, California, United States
Background: Congenital Hypothyroidism (CH) is a known cause of severe neurodevelopmental impairment. Very preterm (VPT)(gestational age ≤32 weeks) and very low birth weight (VLBW) (< 1,500 grams) are at a higher risk for thyroid abnormalities, and many authorities recommend repeat thyroid screening in this vulnerable population. TSH and Free T4 (FT4) levels change significantly in the first few weeks of life, and their reference ranges in preterm infants are not widely known. Objective: The goals of this study are to identify reference ranges and cutoff values for thyroid re-screening in VPT/VLBW infants at one month of age. Design/Methods: This is a retrospective chart review of VPT and VLBW infants admitted to UCI Medical Center and born between 1/1/2012 and 12/31/2020. Repeat thyroid screens, consisting of TSH and FT4, were performed at one month of life (+ 14 days) using Beckman Dxl800 two-step enzyme immunoassay. Thyroid repeat screening data was collected via chart review. Demographic data and short-term outcomes were prospectively collected as part of enrollment in the California Perinatal Quality Care Collaborative (CPQCC). Exclusion criteria included congenital malformation, death, discharge before 30 days of age, or out-born infants admitted to UCI outside the screening window. Results: 430 patients were included. Average gestational age and birthweight of the cohort were 1048 g and 27.8 weeks, respectively. Other maternal and demographic data are shown in table 1.Fifth, 10th, 90th and 95th percentiles for TSH and FT4 are shown in table 2. Tenth and 90th percentiles for TSH differed significantly based on birthweight (BW) but not gestational age (GA). Ninetieth percentile TSH for infants with BW below 1000 g was 7.18versus 5.2 µIU/mL for those with BW >1000 g. Sixty-four patients (14.8%) had TSH >5 µIU/mL and twenty patients (4.6%) had FT4 < 0.8 ng/dL. Using 90th percentile cutoff for TSH would have decreased the incidence of delayed TSH rise from 14.8% to 9.5% and spared 23 patients (36%) the need for follow up on “abnormally elevated TSH”. Atypical CH requiring thyroxine treatment through NICU discharge was diagnosed in six patients (incidence of 1.4%), all of them would have been identified using 90th percentile cutoff for TSH (100% sensitivity); none were identified by State NBS.
Conclusion(s): Repeat thyroid screening with TSH using birthweight based cutoff values of 90th percentile (7.18 µIU/mL for BW below 1000 g and 5.2 µIU/mL for BW above 1000) at one month of age in VPT/VLBW infants seems an appropriate strategy to identify atypical CH requiring thyroxine therapy.
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