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Neonatal TSH levels as an index of iodine sufficiency: differences related to time of screening sampling and
Laura Gruñeiro-Papendieck1, Ana Chiesa, Virginia Mendez
1Fundación de Endocrinología Infantil, División de Endocrinología, Hospital de Niños R. Gutiérrez, Buenos Aires, Argentina. lauragru@cedie.org.ar
Insights
Neonatal TSH screening in Buenos Aires indicates iodine sufficiency, aligning with WHO guidelines for newborns over 48 hours old. However, TSH testing on cord blood or younger infants may yield inaccurate results due to methodology variations.
Area of Science:
- Endocrinology
- Public Health
- Neonatal Screening
Background:
- Current WHO guidelines recommend <3% of newborns have neonatal TSH levels >5 mU/l for adequate iodine intake.
- Assessing neonatal thyroid-stimulating hormone (TSH) levels is crucial for monitoring iodine status in populations.
Purpose of the Study:
- To evaluate if the WHO criterion for neonatal TSH levels (>5 mU/l) aligns with traditional iodine status indicators in Buenos Aires.
- To determine if TSH measurement methodology and specimen timing affect the assessment of iodine sufficiency in newborns.
Main Methods:
- Thyroid-stimulating hormone (TSH) was measured using immunofluorometric assay (IFMA) and immunoradiometric assay (IRMA) on blood samples from newborns at different ages.
- Urinary iodine levels and goiter prevalence were assessed in school-aged children (SAC) for comparison.
- WHO ICCIDD absolute criteria were applied to all tested newborn populations.
Main Results:
- TSH levels >5 mU/l were observed in 11.3% of cord blood samples and 3.6% of samples from infants <48 hours old.
- For newborns >48 hours old, TSH levels >5 mU/l were 2.7% (IFMA, iodine sufficient) vs. 30% (IRMA, moderate iodine insufficiency).
- Median urinary iodine (143 µg/l) and goiter prevalence (4.5%) in SAC indicated iodine sufficiency.
Conclusions:
- Neonatal TSH levels in Buenos Aires align with WHO criteria for iodine sufficiency when applied to newborns >48 hours old using IFMA.
- Using cord blood or samples from infants <48 hours old, or employing different TSH measurement assays, can lead to misinterpretations of iodine status.
- Standardized methodologies and appropriate sampling times are essential for accurate neonatal screening and iodine status assessment.
Introduction:
Current WHO guidelines consider that under adequate iodine intake <3% of newborns should have neonatal TSH levels of >5 mU/l blood when screening is performed in cord blood or at 3 days to 3 weeks of age.
Objective:
To estimate whether this absolute criterion when applied to newborns older than 48 h of age and native to Buenos Aires coincides with the traditional ones (goiter and urinary iodine in school-age children (SAC)), and if the evaluation varies with either the methodology used for TSH measurements and/or the time of specimen sampling.
Population And Methods:
TSH was measured by an immunofluorometric assay (IFMA) on filter paper blood spots of 186 cord blood samples, 112 babies <48 h of age and 1,500 newborns >48 h of age, and by immunoradiometric assay (IRMA) in 238 newborns. The WHO ICCIDD absolute criteria were applied to each population. Thyroid volume was assessed by direct palpation in 500 SAC, and in 100 of them urinary iodine levels were measured.
Results:
TSH levels were >5 mU/l blood in 11.3% of the cord blood samples and in 3.6% of the samples from babies <48 h of age, suggesting mild iodine deficiency. TSH was >5 mU/l in 2.7% of newborns >48 h of age tested by IFMA (iodine sufficient) and in 30% measured by IRMA (moderate iodine insufficiency). Median urinary iodine and goiter prevalence in SAC were 143 mug/l and 4.5%, respectively, as expected in an iodine-sufficient area. conclusion: The TSH levels in Buenos Aires conform with the WHO criterion that defines iodine sufficiency. Application of this criterion, however, to cord blood samples or samples from babies <48 h old and the use of different methodologies may lead to erroneous conclusions.
