A novel point-of-care device accurately measures thyrotropin in whole blood, capillary blood and serum

Determination of Capillary Blood TSH and Free Thyroxine Levels Using Digital Immunoassay

Background

The remote performance of thyroid function blood tests is complicated because it requires blood collection.

Objective

To compare TSH and free thyroxine (FT4) levels between capillary and venous blood and assess the adequacy of measuring each value in capillary blood.

Methods

This prospective intervention study was conducted at Ito Hospital and was based on the clinical research method. The participants were 5 healthy female volunteers and 50 patients (41 females and 9 males) between the ages of 23 and 81 years. To measure TSH and FT4 levels in capillary and venous blood, a digital immunoassay (d-IA) method capable of measuring trace samples was used. Chemiluminescence measurements were used as controls. Values obtained for each assay system were compared using Spearman's correlation analysis. Capillary blood was collected using an autologous device (TAP II; not approved in Japan).

Results

Capillary plasma volume obtained using TAP II was 125 µL or more in 26 cases, 25 µL to 124 µL in 24 cases, and less than 25 µL in 5 cases. Strong correlations were noted in the TSH and FT4 levels between capillary and venous blood, with correlation coefficients of rs = 0.99 and rs = 0.97, respectively.

Conclusion

Capillary TSH and FT4 levels strongly correlate with venous blood values. Trace samples can be used in high-precision d-IA methods. These results may promote telemedicine in assessing thyroid function.

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.