Confirmation of neonatal screening: reference intervals and evaluation of methodological changes in TSH measurement

Area of Science:

• Pediatric Endocrinology
• Neonatal Screening
• Clinical Chemistry

Background:

• Limited neonatal reference values for serum thyrotropin (TSH) exist.
• Methodological changes in IMMULITE TSH measurement kits occurred in 2006.
• Accurate TSH levels are vital for neonatal thyroid screening.

Purpose of the Study:

• To validate methodological changes in TSH measurement kits.
• To establish new reference intervals for neonatal and infant serum TSH.
• To improve the interpretation of borderline TSH measurements in newborns.

Main Methods:

• Validation of methodological changes using 80 patient serum samples.
• Analysis of 334 neonates and infants divided into four age groups (48-72h, 7-10 days, 11-14 days, 28-40 days).
• Determination of TSH reference intervals (2.5th-97.5th percentile).

Main Results:

• Current kits overestimate TSH results by 26% to 37%.
• Established TSH reference intervals: G1 (1.1-12.7 mIU/L), G2A (1.8-9.8 mIU/L), G2B (1.1-7.1 mIU/L), G3 (1.2-6.9 mIU/L).
• Significant difference in TSH intervals between early (7-10 days) and late (11-14 days) second week of life (p < 0.03).

Conclusions:

• New IMMULITE kits require updated neonatal TSH reference intervals.
• Consider dividing reference values into early and late stages during the second week of life.
• Improved interpretation of borderline newborn screening results is needed.