High-sensitive Detection and Quantitation of Thyroid-stimulating Hormone (TSH) from Capillary/fingerstick and Venepuncture Whole-blood Using Fluorescence-based Rapid Lateral Flow Immunoassay (LFIA)

Background: In the last decade, point of care testing (POCT) such as lateral flow immunoassays (LFIA) were developed for rapid TSH measurement. Most of these TSH-LFIAs are designed for qualitative measurements (i.e., if TSH values > 5, or >15 IU/L) and as screening tests for primary hypothyroidism in children and adults. Serum or plasma, but not venepuncture whole-blood or fingerstick/capillary, are usually used to quantify TSH accurately. Studies on performance evaluation of TSH-LFIAs POCT using venepuncture or fingerstick whole-blood are limited. Additionally, limited studies evaluated the performance and validity of TSH-LFIAs POCT compared to valid and reliable reference methods. To our knowledge, this is the first study to evaluate three different blood withdrawal techniques for evaluating POCT of TSH.

Aim: We aim to evaluate the performance of a new fluorescence-based LFIA and its Finecare™ fluorescent reader for quantitative measurement of TSH from a fingerstick, venepuncture whole-blood, and serum.

Methods: 102 fingerstick, venepuncture whole-blood, and serum samples (with normal and abnormal TSH values) were analyzed by Finecare™ Rapid Quantitative LFIA test and Roche CobasPro-c503 as a reference test.

Results: Using serum, when compared to CobasPro-c503 reference method, Finecare™ showed high sensitivity [90.5 % (69.6-98.8)] and specificity [96.3 % (89.6-99.2)] for diagnosis of thyroid abnormalities (<0.35 or >4.5 mIU/L). The actual test values (mIU/L) of Finecare™ showed excellent agreement (Cohen's Kappa = 0.85) and strong correlation (r = 0.93, p < 0.0001) with CobasPro-c503. Using venepuncture whole-blood samples, Finecare™ showed similar results to serum with high sensitivity [95.2 % (76.2-99.9)], specificity [97.5 % (91.4-99.7)], excellent agreement (Cohen's Kappa = 0.91), and very strong correlation (r = 0.95, p < 0.0001) with CobasPro-c503. These results suggest that Finecare™ can be used for quantitative measurement of TSH using serum or venepuncture whole-blood. These key performance indicators were slightly decreased when fingerstick whole-blood samples were used: sensitivity [85.7 %(63.7-97)], specificity [90.0 %,(81.5-96)], good agreement (Cohen's Kappa = 0.7) and very strong correlation (r = 0.9, p < 0.0001) with CobasPro-c503. A subgroup analysis of abnormal TSH samples revealed a strong and significant correlation between the reference, Finecare™ whole-blood (r = 0.692; p = 0.0015), and fingerstick test Finecare™ (r = 0.66; p = 0.0025). A very strong correlation was also observed between Cobaspro-c508 serum and Finecare™ serum (r = 0.88; p < 0.0001). Conclusion: In comparison to the reference assay, our study demonstrates that Finecare™ exhibits high sensitivity, specificity, agreement, and a strong correlation. These findings provide evidence that Finecare™ is a reliable, valid, and accurate point-of-care test for TSH screening and quantitative measurement, especially in non- or small laboratory settings.