Effect of Fasting and Postprandial Blood Samples in Results of Thyroid Function Tests Among Euthyroid People and Patients with Thyroid Problems: A Systematic Review and Meta-Analysis

Abstract

Abstract Introduction/Objective Thyroid disorders are considered to have a significant global health impact, affecting around 200 million people, and about 5% of all populations are diagnosed with hypothyroidism. Thyroid problems are mainly diagnosed by the laboratory’s thyroid function tests (TSH, FT4, and FT3), and currently, there is no special guideline for a preferred sample to test the thyroid functions. Aim To investigate whether using a fasting serum sample or postprandial serum sample could affect the results of the thyroid function tests in both euthyroid people and patients with thyroid problems. Methods/Case Report • A systematic search was done on PubMed, EMBASE, Google Scholar, Semantic Scholar, and manual searches with cross-referencing. • PECOS framework was used for developing the research question. • PRISMA guidelines used for the methodology. • Two meta-analyses for TSH and FT4 were done based on the participant’s thyroid status, and one meta-analysis done for the FT3 for all. • Statistical analyses were done using Revman5 software. Results (if a Case Study enter NA) • Ten full-text studies and three abstracts were included for the systematic review, and for meta-analysis, nine full-text studies and two abstracts. • Based on the Cochrane rule of thumbs of the effect size interpretations, the meta-analyses result showed a statistically significant moderate effect for TSH mean differences; Mean of fasting blood sample > mean of the postprandial sample. • TSH effect for euthyroid people based on results of 9 studies from 641 participants (MD, 0.58; Fixed, 95% CI: [0.44 to 0.73], p. <.00001). • TSH results for all based on results of 11 studies from 921 participants (SMD, 0.46; Random, 95% CI: [0.31 to 0.61], p. <.00001). • No statistically significant effect for FT4 and FT3 mean differences results. • Publication bias is suggested for TSH and FT3 results due to the asymmetrical appearance, but not for FT4. Conclusion • In conclusion, the use of fasting blood samples would have a significantly higher TSH result value compared to the postprandial blood samples. Hence, it may help introduce a new guideline to standardize the blood sampling status for the TSH test screening and diagnosis. Alternatively, different reference ranges depending on the sampling status might be suggested, which might help promote the patients’ quality of life and reduce healthcare costs.