Screening for hypothyroidism in down syndrome using the capillary thyroid stimulating hormone method

Objectives To analyze data from the Scottish capillary thyroid stimulating hormone (TSH) screening program for hypothyroidism in Down syndrome to identify a threshold for capillary TSH elevation below which low venous free thyroxine (fT4) (<9 pmol/L) and/or frank venous TSH elevation (>10 mU/L) range is unlikely. Study design Review of proformas prospectively submitted on all children with Down syndrome referred via the screening program between 2003 and 2013. Results Ninety-nine patients with Down syndrome (50 females, 49 males) were identified, 76 school-age (≥5 years) and 23 preschool (<5 years), mean (range) age at referral 9.4 (0.9-18.1) years. Pearson correlation between capillary TSH and venous TSH was 0.814; between capillary TSH and venous fT4 -0.522 (P = .01). Receiver operator curve analysis showed that capillary TSH values of 4 and 6 mU/L were 95.9% and 73.5% sensitive, 5.8% and 80.8% specific, respectively, in predicting venous TSH >10 mU/L. Fifty-three children had capillary TSH values of 4-5.9 mU/L of whom only one, a boy of 15.8 years, had subnormal venous fT4 (<9 pmol/L), and venous TSH >10 mU/L was found in 13 (4 preschool). Conclusions Venous fT4 is normal in almost all patients with Down syndrome with capillary TSH 4-6 mU/L. We propose an algorithm incorporating rescreening by finger prick after 6 months, rather than venepuncture, in schoolaged children with borderline capillary TSH elevation. Further data are needed before this approach can be recommended for preschool children.