Comparison of Enzyme-Linked Immunosorbent Assay and Lateral Flow Assay to Measure Thyroid-Stimulating Hormone and Free T4 in Human Serum

Background: Thyroid disorders affect millions of people around the world, mainly women. Measurement of hormones is critical in their identification, treatment, and monitoring; Therefore, the methods must be as reliable and valid as possible. Methods: We designed a cross-sectional study to compare thyroid-stimulating hormone (TSH) and free tetraiodothyronine (fT4) concentrations using ELISA (Enzyme-Linked Immunosorbent Assay) and LFA (Lateral Flow Assay) in human serum samples. We obtained 96 serum samples that were evaluated with a commercial kit for ELISA (Accubind Monobite, Lake Forest, California, US) and LFA (Micropofit Fluorecare, Guangdong, Shenzhen, China). We used the Wilcoxon nonparametric test, Bland–Altman, and Passing-Bablok regression to compare TSH and fT4 concentrations obtained by ELISA and LFA. Results: The median TSH concentrations obtained by ELISA and LFA were 1.92 and 2.11 μIU/mL, and for fT4 were 1.14 and 1.10 ng/dL. On the other hand, the Spearman's rho between ELISA and LFA for TSH was 0.845. The TSH concentrations between ELISA and LFA had significant differences (p < 0.05). About fT4, the Spearman's rho between methods was 0.348. The bias for TSH was −0.315, and for fT4 was −0.013. The Deming regression for TSH (p = 0.309) and fT4 (=0.938) shows that the levels obtained by both methods do not present significant differences, and the Passing-Bablok regression identifies significant bias between both methods, especially for fT4, in the range of concentrations studied. Conclusion: TSH measurement by LFA may be a viable alternative to evaluate thyroid diseases, but fT4 by LFA is not precise and presents a high bias.