Capillary blood screening for hypothyroidism in Down syndrome?

Abstract

Children and adolescents with Down syndrome carry a lifelong increased risk of acquired hypothyroidism, particularly from autoimmune disease. Their hypothyroidism can be difficult to detect clinically, as symptoms such as short stature, constipation, dry skin, and lethargy occur commonly in these children. Thus, multiple societies have endorsed various thyroid hormone screening guidelines, based upon venipuncture. Screening programs are almost always debated and need to take into account disease prevalence, test sensitivity and specificity, cost of screening, and test acceptability, among other factors. In this issue of The Journal, McGowan et al consider whether the Scottish capillary thyroid stimulating hormone (TSH) screening program might contain data to establish a threshold value below which low venous free T4 and elevated venous TSH are unlikely, so that capillary blood screening could serve as a first-stage screening for children in lieu of venipuncture. Using a limited cohort of 99 children with Down syndrome identified over 10 years by capillary TSH ≥ 4 mU/L, they determine that a cutoff TSH value of 6 mU/L was 73.5% sensitive and 80.8% specific in predicting venous TSH >10 mU/L. Correlation between capillary TSH and venous free T4 was low. The authors propose an algorithm for management based upon capillary TSH. For any child with capillary TSH > 6 mU/L, they recommend clinical assessment and immediate venipuncture. For those children <5 years of age with capillary TSH in the 4-5.9 mU/L range they also suggest immediate venipuncture. In those children aged 5 years and older with a result in the 4-5.9 mU/L range, they suggest repeat capillary screening six months later because decompensated hypothyroidism was so rare in these patients, only 1 of 38. Whether their less invasive and likely less expensive approach should be adopted more globally will require additional study. Article page 1013▶ Screening for Hypothyroidism in Down Syndrome Using the Capillary Thyroid Stimulating Hormone MethodThe Journal of PediatricsVol. 166Issue 4PreviewTo 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. Full-Text PDF