Age- and Gender-Specific Changes in Thyroid Size and Thyroid Function Test Values of Euthyroid Subjects

Abstract

Background: The thyroid status is evaluated by two clinical diagnostic tests which are thyroid ultrasonography and thyroid function tests. The objective of this research is to critically analyze the age and gender based variations of thyroid volume and thyroid hormone levels in the hospital based euthyroid subjects. Methodology: A total of 221 euthyroid subjects aged 1 - 86 years were selected to observe the normal thyroid size by ultrasonography at Department of Radiology and the thyroid function test values (FT3, FT4 and TSH) of 2413 euthyroid subjects aged (<1)-93 years were observed at Department of Biochemistry, Tribhuvan University Teaching Hospital, Kathmandu, Nepal during January 2017 to February 2018. The observed data were analyzed graphically and statistically to check the cross-correlations among the variables. Results: The best fitted equations with significant correlation coefficients and p < 0.05 provide the empirical relations between any two of the observed variables: age, thyroid lobe volumes, FT3, FT4 and TSH. The mean ± SD (p < 0.0001) of thyroid volume, FT3, FT4 and TSH are 4.74 ± 2.30 mL, 5.46 ± 0.82 pmol/L, 14.09 ± 2.71 pmol/L and 2.30 ± 0.98 mIU/L, respectively. Conclusion: The thyroid size first increases and then decreases whereas the thyroxin level first decreases and then increases with aging. Left lobe volume is almost same for both genders and right lobe volume is higher in males. The thyroid size in menarche and menopause periods of females is larger than that of males. Such age- and gender-specific changes recommend the new reference ranges for the normal thyroid functions.