Thyroid hormones and glycosylated hemoglobin (HbA1) in Juvenile Diabetes Mellitus (JDM)

Abstract

In 60 newly diagnosed children with JDM we measured serum T4, T3, reverse T3 (rT3) and free T4 (FT4) before and serially at 1, 3 and 5 days and up to 6 months during therapy. The mean ± SEM serum T3 before therapy (71 ± 6 ng/dl) was lower (p<.01) compared to day 5 (96 ± 5) and the T3 on day 5 was lower than controls (126 ± 9) but was normal by 1 month. Mean serum rT3 before therapy (60 ± 3 ng/dl) was higher (p<.001) compared to day 5 (38 ± 2), but day 5 did not differ from controls (32 ± 3). FT4 levels were higher (p < .01) than controls and remained unchanged. Serum TSH was normal throughout. Serum T4 was normal and remained unchanged in patients with −HCO3 > 15 mEq/L, but low before therapy when −HCO3 < 15 and increased to normal by day 3. Serum T3 was lower in patients with low −HCO3 before therapy. The elevated rT3 and FT4 were unaffected by low −HCO3. HbAl fell significantly by paired t test (p < .001) during the first 5 days of therapy, and further decreased during the ensuing 3 months (p < .001). HbA1 correlated with rT3 and inversely with T3 during the study period (p < .001). We speculate that the metabolic disturbance in untreated JDM resembles the "Low T3 Syndrome" of starvation. The association of low −HCO3 and low total T4 and T3 but normal TSH and high FT4 suggests an impairment of binding to the serum thyroid binding proteins. Correlation of T3 and rT3 with HbAl may reflect their dependency on the severity of the disease.