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Diminished thyroxine-binding globulin in pubertal diabetic children
M H Connors1, D B Dunger, H Chapel
1Department of Pediatrics, University of California, Davis, USA. mhconnors@ucdavis.edu
Objective:
To determine the effect of diabetes on thyroid hormone and thyroxine-binding globulin (TBG) concentrations during puberty.
Research Design And Methods:
Total thyroxine (TT4), free thyroxine (FT4), and TBG levels of 171 thyroid microsomal antibody-negative subjects with normal thyroid-stimulating hormone (TSH) levels were measured and compared with those of nondiabetic adolescents. A random subset of 68 diabetic patients (40 boys and 28 girls) and 51 control subjects (24 boys and 27 girls) were analyzed for puberty-related changes.
Results:
Most TT4 levels of diabetic subjects (80% of girls and 63% of boys) were below the 50th percentile for the normal range. TT4 increased with age in girls (r = 0.25, P < 0.04) but not in boys. FT4 was within normal limits in both sexes. TBG measurements were below the 50th percentile and 20% were below the 95% CI for both sexes; TT4 correlated with TBG in boys (r = 0.54, P < 0.001) and in girls (r = 0.58, P < 0.001). Duration of diabetes had no effect, whereas TT4 and FT4 levels were higher in girls with the lowest HbA1 levels (r = -0.29, P < 0.01 and r = -0.45, P < 0.01). Levels of TBG were reduced for all male pubertal stages (P < 0.01) and for early and late female pubertal stages (P < 0.01). There was no direct relationship between glucose control or the duration of diabetes and levels of TBG.
Conclusions:
Because TT4 levels are low and correlate with the low levels of TBG, it is important to measure free thyroid hormone and TSH levels in diabetic adolescents to establish euthyroidism.