Evalution of Thyroid Functions in Hemodialysis Children in Sohag University Hospital

Thyroid gland and its hormones play an important role in organ development and the homeostatic control of many physiological mechanisms such as body growth and energy expenditure. The two main thyroid hormones are triiodothyronine (T3) and thyroxine (T4) affect renal development and metabolism so any impairment in thyroid functions lead to or aggravate kidney diseases.

On the other hand, kidneys play an important role in the thyroid metabolism as it normally contributes to the clearance of iodide, primarily by glomerular filtration. Among patients with renal failure, there is diminished iodide excretion and an increase in plasma inorganic iodide, which results in increased uptake of the iodide by the thyroid gland. Increases in total body inorganic iodide can potentially block thyroid hormone production (the Wolff-Chaik off effect). Such a change may explain the slightly higher frequency of goiter and hypothyroidism in patients with chronic kidney diseases.

The kidneys affect the hypothalamic pituitary-thyroid axis, so any impairment in kidney functions leads to disturbed thyroid physiology. All levels of the hypothalamic-pituitary-thyroid axis may be involved, including alterations in hormone production, distribution, and excretion.

End stage renal disease (ESRD) and hemodialysis (HD) affect the levels of all thyroid hormones. The earliest and the most common thyroid function abnormality in patients with ESRD on HD is low T3 level (especially total T3 than free T3). This is called 'low T3 syndrome. The prevalence of subclinical hypothyroidism has been reported to be much higher in patients with ESRD on HD than in the general population.

Due to similarity of signs and symptoms, sometimes it is difficult to identify subjects with ESRD also has hypothyroidism; therefore, different studies have been carried out to establish the incidence of these conditions.