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Revised TSH thresholds increase congenital hypothyroidism by 15% in New Zealand
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A national screening program produced a 15% increase in the detection of congenital hypothyroidism, researchers in New Zealand found.
“Given the success of screening for congenital hypothyroidism and the inevitable drive to diagnose and treat increasingly milder disease, [thyroid-stimulating hormone] cut-offs have decreased markedly from inception,” Natasha L. Heather, MD, of the New Zealand Newborn Metabolic Screening Program and Starship Children’s Hospital in Auckland, and colleagues wrote. “The current screening dilemma is to define optimal TSH thresholds that appropriately balance the benefits of disease detection with harms from false-positive results in healthy infants.”
In 2013, the TSH threshold used to trigger clinical referral in the New Zealand Newborn Metabolic Screening Program was reduced from 50 mIU/L to 30 mIU/L. In the current study, Heather and colleagues aimed to determine whether the revised screening algorithm increased the number of infants diagnosed with congenital hypothyroidism over a 24-month period.
Researchers reviewed data from the screening program, which referred infants with TSH levels ≥ 50 mIU/L to pediatric endocrinologists from 1997 to 2012. From 2013 onward, that threshold was reduced to ≥ 30 mIU/L, and all newborns aged 14 days or older with a second TSH level ≥ 8 mIU/L were automatically referred to an endocrinologist for further evaluation. The researchers obtained data from 2013 and 2014, and evaluated the impact of the new protocols (n = 117,528).
Screening led to diagnosis of 52 cases: 47 in the general screening population and five in infants with low birth weight, who underwent repeat screening. One case went undetected. Thirty-two newborns with TSH levels ≥30 mIU/L were referred after a median 9 days (range, 5-14 days), and another 15 with TSH levels from 15 mIU/L to 29 mIU/L received referrals after a median of 20 days (range, 9-52 days; P < .001). Heather and colleagues wrote that all directly referred babies had confirmed cases of congenital hypothyroidism, and the reduced cut-off for second samples detected an additional six cases (15%) compared with previous standards.
“Overall, we have shown improved performance of the New Zealand national newborn screening program for congenital hypothyroidism, through a small reduction in the TSH cut-off applied to second samples,” Heather and colleagues wrote. “Over 2 years, this led to the detection of a number of cases that would previously have been missed, with a minimal increase in either clinical workload or anxiety for families of healthy infants. As a result of this study, the New Zealand program has further reduced the TSH threshold for direct notification. It is also clear that further long-term data on infants with mild, transient and subclinical hypothyroidism are urgently needed to inform screening policy.” – by Andy Polhamus
Disclosure: Heather and Webster report employment with the New Zealand Newborn Metabolic Screening Program. No other authors report any relevant financial disclosures.
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