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Neonatal screening for congenital hypothyroidism: Time to lower the TSH threshold in France
L Levaillant1, F Huet2, P Bretones3
1Department of Pediatric Endocrinology and Diabetology, University Hospital of Angers, 4 rue Larrey, Angers 49000, France; Reference Center for Rare Diseases of Thyroid and Hormone Receptivity, University Hospital of Angers, 4 rue Larrey, Angers 49000, France.
Insights
Lowering the TSH screening threshold in France could identify more congenital hypothyroidism (CH) cases, potentially preventing cognitive deficits. This evaluation is crucial for timely levothyroxine treatment in newborns.
Area of Science:
- Neonatal screening
- Endocrinology
- Public health
Background:
- Congenital hypothyroidism (CH) screening in newborns uses thyroid-stimulating hormone (TSH) on dried blood spots.
- Prompt levothyroxine treatment before day 15 prevents irreversible mental retardation.
Purpose of the Study:
- Evaluate lowering the French TSH screening threshold (currently 17 mIU/L).
- Assess the impact on CH diagnosis rates and case classification (transitory vs. permanent).
- Analyze the cost-effectiveness of a lower TSH threshold strategy.
Main Methods:
- Analysis of TSH levels in dried blood spots from newborns in France.
- Comparison of the current high TSH threshold with international standards (6-12 mIU/L).
- Review of studies linking sub-threshold TSH levels to cognitive development.
Main Results:
- The French TSH threshold of >17 mIU/L may miss up to 30% of CH cases, including permanent forms.
- Mild CH, missed by the current threshold, is associated with cognitive impairments.
- An inverse relationship exists between screening TSH levels and later cognitive development.
Conclusions:
- Lowering the TSH screening threshold in France is warranted to improve CH detection.
- Early identification and treatment of mild CH may prevent cognitive deficits.
- Further studies are needed to confirm the number of new cases and cost-effectiveness.
Abstract:
Neonatal screening for congenital hypothyroidism (CH) is based on the measurement of thyroid-stimulating hormone (TSH) in whole dried blood samples on filter paper in all newborns. The objective of screening for CH is to prevent mental retardation, which is irreversible in the event of a late diagnosis, by setting up prompt treatment (before day 15) with levothyroxine. The threshold value of TSH on filter paper on day 3 is 17 mIU/L in France in the GSP method (GSP, Genetic Screening Processor, Perkin Elmer): It is one of the highest thresholds used in the world. In many countries, the TSH threshold is between 6 and 12 mIU/L. Studies have found that a threshold of > 17 mIU/L may miss as much as 30% of cases of CH, with 30-80% of these being permanent CH. Recent studies suggest that mild CH (currently missed by the French TSH threshold) is associated with cognitive consequences if left untreated. An inverse relationship between TSH at screening (below the current threshold) and cognitive development at preschool or school age has been shown. These studies advocate for the evaluation of a lowering of the threshold of TSH on filter paper in France: (a) to determine the number of CH diagnoses with the new threshold and whether these "new cases" would be transitory or permanent; and (b) to analyze the cost-effectiveness of the strategy.
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