This epidemiological study investigated the proposed relationship between three parameters of thyroid function - thyroxine (T4) triiodothyronine uptake (T3U) and thyroid stimulating hormone (TSH), and various diseases in a population of N.S.W. children of varying age, who underwent blood screening for thyroid function at the Royal Alexandra Hospital for Children between 1980 and 1990. Age, sex, puberty and year of diagnosis were identified as potential confounders in the study and various measures taken to control for these factors in the analysis. The study population was divided into two broad categories: patients aged less than 3 years of age and, patients aged 3-18 years of age. The main analysis concentrated on the 3-18 year age group. A Short Stature diagnostic group was selected as a control group in this category. As the diagnostic groups identified varied in normality, the Wilcoxon Rank Sum Test was used for significance testing of the data. Seventy-eight separate diagnostic groups were identified in patients aged 3-18 years. Twenty-one diagnostic groups showed a
statistically significant mean difference (p < 0.05) for T4 between the cases and the control group. Ofthese, the following diagnostic groups were selected for analysis and found to have a significantly low T4 compared to the control group: Selected Diabetes, Thalassaemia, Growth Hormone Deficiency, Anorexia Nervosa, Acute Lymphoblastic Leukaemia, various Psychological disorders and Cystic Fibrosis. The following diagnostic groups were found to
have a significantly high T4 compared to the control group: Obesity, Deafness, Failure to
Thrive, Slipped Epiphyses, Turner's Syndrome and Juvenile Chronic Arthritis. These groups
were stratified by sex and puberty (3-11 years and >11-18 years) and similarly analysed. A further analysis was performed in order to produce an odds ratio. These diagnostic groups seemed to affect thyroid function in either of three different ways. Conditions affecting the thyroid gland directly were reflected in the results for T4. Conditions affecting protein binding mechanisms were reflected in the results for T3U and conditions which affect the hypothalamic-pituitary axis were reflected in the results for TSH. The literature generally supported the findings of this study.