The relationship of insulin-like growth factor-I to total thyroxine in normal and low birth weight infants.
IGF-I concentrations were determined by RIA in eluates of dried blood collected on filter paper from infants who ranged in age from 3 to 21 d. The infants were separated into normal (greater than 2.5 kg) and low (less than 2.5 kg) birth wt groups and further subdivided on the basis of normal (greater than 83.7 nmol/liter) or low (less than 64.4 nmol/liter) levels of thyroxine. Both the normal and low birth wt groups whose blood thyroxine was in the normal range had similar mean IGF-I values during the 1st wk of life that were significantly higher (p less than 0.05) than those of either the normal or low birth wt groups whose thyroxine concentrations were below normal. Infants older than 1 wk of age with normal birth wt and normal thyroxine levels had significantly greater (p less than 0.05) mean IGF-I values than those of any of the other groups. Infants in the low birth wt-normal thyroxine group exhibited modest increases in IGF-I levels after the 1st wk of life that were significantly greater (p less than 0.05) than those found in the low birth wt-low thyroxine infants. These studies have demonstrated that IGF-I concentration is correlated positively with total thyroxine and with birth wt and that the latter is confounded by the former.
Mitchell
M L
ML
Massachusetts Department of Public Health, Newborn Screening Program, Jamaica Plain 02130.
Hermos
R J
RJ
Feingold
M
M
Moses
A C
AC
D006801:Humans; D007230:Infant, Low Birth Weight / Q000097:blood*; D007231:Infant, Newborn; D007334:Insulin-Like Growth Factor I / Q000097:blood*; D011863:Radioimmunoassay; D013002:Somatomedins / Q000097:blood*; D013974:Thyroxine / Q000097:blood*
D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013974:Thyroxine