The conversion of pmol/L to pg/mL, the unit of measurement most often used in the US for free T3, uses the conversion factor of 1.536. The pmol/L number is divided by 1.536 to get pg/mL. The conversion of pmol/L to ng/dL, the unit of measurement most often used in the US for free T4, uses the conversion factor of 12.9. The pmol/L number is divided by 12.9 to get ng/dL.
The results from Kapelari's study are converted to US units of measurement and summarized in Table 1.
Table 1. Results from "Pediatric reference intervals for thyroid hormone levels from birth to adulthood: a retrospective study" converted to US units of measurement.
A reference range for reverse T3 in infants and children has not yet been established nor has it adequately been studied. However, some studies do exist. Researchers at UCLA studied levels of T4, T3 and reverse T3 in neonates from 1-30 days old. They found that " high serum rT3 concentration in the newborn becomes comparable to that in the normal adult by 9-11 days of neonatal life." ( Chopra, 1975 ) The same dramatic decrease in reverse T3 in newborns was reported by Dr. Brown and Feingold in 2010 as seen in Image 7. ( Brown, 2010 ) A striking increase in T3 levels after birth was noted by both studies as well. Reference range for reverse T3 in adults has been established to be 10-24 ng/dL. ( Endocrine Society Laboratory Reference Ranges ) Unfortunately, until further studies are conducted the only information available today regarding reverse T3 in infants is to use that of adults.
Image 7. Source: Shiri B. Feingold, Rosalind S. Brown, Neonatal Thyroid Function, NeoReviews Nov 2010, 11 (11).
In short, hypothyroidism should not be missed in any infant or child given the important role thyroid hormone plays in the health and development of children. Signs and symptoms should never be ignored and a complete and thorough check of all thyroid hormone levels should be conducted.
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