To Establish the Reference Range of Free Thyroid Hormones

Thyroid disorder is common worldwide. In India, there is significant burden of thyroid disease. According to the projection from various studies, it has been estimated that 42 million people in India suffer from thyroid disease. Usually, total serum T3, T4 and TSH are used in biochemical analysis. Gradually, the trend is shifting from total serum T3, T4 to free T3 (FT3), free T4 (FT4) which are biologically more active. However, the reported reference range varies so that every laboratory has to establish its own reference range. Aim was to establish the reference range of serum FT3 and FT4 in our hospital laboratory and compare it with the values reported by other standard laboratories. The study was conducted in the Department of Biochemistry, Maharishi Markandeshwar Institute of Medical Sciences and Research (MMIMSR), Mullana, Ambala, Haryana. 32 apparently healthy euthyroid subjects were selected and divided into 2 groups. Group 1: 7 male subjects; Group 2: 25 female subjects. 5 ml of fasting venous blood was collected from antecubital vein under aseptic conditions from each subject into plain vials. Serum was separated and FT3, FT4, TSH were estimated by ELISA. In females, serum FT3 levels were 2.55 [+ or -] 1.16 pg/ml, FT4 levels were 1.23 [+ or -] 0.37 ng/ dl and TSH levels were 2.40 [+ or -] 1.56 pIU/ml, whereas the corresponding values in males were 2.93 [+ or -] 1.11 pg/ml, 1.26 [+ or -] 0.39 ng/dl and 1.92 [+ or -] 2.86pIU/ml respectively. Overall ranges were 2.64 [+ or -] 1.17 pg/ml, 1.23 [+ or -] 0.42ng/dl and 2.75 [+ or -] 2.87pIU/ml respectively which are comparable (P>0.05) to those reported by other laboratories, e.g. Lal Path Lab (FT3 = 1.4-4.2 pg/ml, FT4= 0.8-2.0 ng/dl, TSH=0.28-6.82 pIU/ml), Thyrocare (FT3=1.7-4.2 pg/ml, FT4=0.70-1.80 ng/dl, TSH= 0.30-5.5 pIU/ml) and SRL (FT3=2.503.90 pg/ml, FT4=0.66-1.20 ng/dl, TSH=0.34-5.60 pIU/ml). Our laboratory levels of free thyroid hormones were comparable with other reference range of different laboratories and thus suitable to be used as reference during analysis of patient samples.