Subclinical hypothyroidism (SCH) is a mild form of hypothyroidism where the TSH levels are slightly above the normal range and T3 & T4 values are within the normal limits. Oxidative stress caused by reactive oxygen species (ROS) causing an imbalance in the antioxidant/oxidant status of an individual is well recognized in hyperthyroidism & overt hypothyroidism but not in (SCH). Recently much attention is focussed on SCH, as it exhibits the same cardiovascular consequences as overt hypothyroidism. The current study evaluates the oxidative stress index (OSI) and the correlation of OSI with thyroid profile and Paraoxonase -1 (PON- 1), the antioxidant enzyme associated with HDL in subjects with subclinical hypothyroidism. OSI was calculated after measuring the total oxidant status (TOS) and total antioxidant status (TAS). This cross-sectional study included 64 subjects with sub-clinical hypothyroidism and 128 subjects with normal thyroid profile. Age of the subjects ranged between 25 and 75 years. Serum levels of TAS, TOS and PON-1 was measured in the subjects whose thyroid profile was determined. OSI was calculated and differences between the variables in the two groups were analysed by the non-parametric tests. Correlation analysis was done by the spearman's test. The diagnostic ability of OSI was assessed by ROC Curve. Significant increase in the OSI and TOS was observed in subjects with SCH. There was no change in the antioxidant status as well as PON-1 activity. OSI can be considered as an efficient marker in the evaluation of oxidative stress.
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