Exploring the Link between Fasting And Postprandial Thyroid Function Tests In Clinical Euthyroidism

Background: Thyroid disorders are common but testing is not standardized for time and prandial state. Subclinical hypothyroidism may be underdiagnosed in postprandial samples. Objective: This study aimed to determine effects of fasting and postprandial state on thyroid function tests (TFTs) in clinically euthyroid patients and to develop a prediction model for fasting TSH if only postprandial levels are available. Methods: This predictive correlational study conducted in King Edward Medical University in 2021 included 95 clinically euthyroid individuals between 18 and 60 years. After obtaining fasting TFTs, mixed-nutrient 400-500 calorie supervised meal was given. After 2 hours, postprandial TFTs were obtained. Data was analyzed using SPSS- 20.0 keeping significant level at p-value <0.05. Chi-square test, paired sample t-test & one-way ANOVA was used for initial analysis, Pearson product moment correlation and simple linear regression for prediction models. Results: The mean age of participants was 27.94±5.90 years with 54(56.84%) being male. Mean Fasting and Postprandial FT3 and FT4 were 4.89±0.99 pmol/L, 4.82±1.05 pmol/L (p= 0.328) & 19.34±4.15, 19.03±3.97 pmol/L (p=0.225) respectively. Fasting (FTSH) and Postprandial TSH (PPTSH) was 1.69±2.34 and 1.48±1.15 mIU/L (p=0.162). Compared to fasting, PPTSH declined in 54(56.8%), rose in 36(37.9%) and remained unchanged in 5(5.3%) cases. There was negative correlation between FTSH and postprandial change (r -0.92, p<0.001) and positive correlation between FTSH & PPTSH (r=0.87, p<0.001). PPTSH predicted FTSH as Fasting TSH = 1.765 PPTSH – 0.923 (p <0.001). Conclusions: PPTSH may predict FTSH but FTSH should be preferred especially in patients with strong suspicion of subclinical hypothyroidism