Reference intervals for neonatal thyroid function tests in the first 7 days of life

Area of Science:

• Neonatal endocrinology
• Clinical biochemistry
• Pediatric diagnostics

Background:

• Neonatal hypothyroidism requires prompt intervention to prevent neurological damage.
• Current thyroid function reference intervals (RIs) are not age-specific for newborns, hindering accurate interpretation.
• Thyroid function parameters like TSH, FT4, and FT3 change rapidly in early neonatal life.

Purpose of the Study:

• To develop hour-specific reference intervals (RIs) for thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free tri-iodothyronine (FT3) in neonates.
• To improve the diagnostic accuracy of neonatal hypothyroidism using data mining techniques.
• To provide clinicians with precise RIs for interpreting neonatal thyroid function tests.

Main Methods:

• Extracted TSH, FT4, and FT3 results from neonates under 7 days old (2005-2015).
• Excluded neonates with multiple tests or known primary hypothyroidism.
• Utilized Monash Pathology database and medical records for data collection and analysis.

Main Results:

• Established hour-based RIs for TSH, FT4, and FT3 for neonates up to 168 hours of life.
• Observed significantly high TSH and FT4 levels within the first 24 hours, followed by a decline.
• Provided specific RI ranges for different age intervals (e.g., 0-24h, 25-48h, etc.).

Conclusions:

• Hour-based RIs for TSH and FT4 are crucial for accurate interpretation in the first 24 hours post-birth.
• The developed RIs facilitate more precise identification of neonates at risk of hypothyroidism.
• Implementing these RIs can lead to earlier and more effective interventions for neonatal thyroid dysfunction.