Comparison of some indicators of the thyroid gland functional activity in simultaneous testing of capillary and venous blood

Background. In clinical practice it is often impossible to draw blood from peripheral veins for laboratory testing. At the same time the problem of comparison of venous and capillary blood parameters is still insufficiently studied.

Aims. To compare 5 laboratory indicators of the thyroid gland function – FT3 (free T3), FT4 (free T4), TgAb (thyroglobulin antibodies), TPOAb (thyroid peroxidase antibodies), and TSH – in order to assess deviations of these parameters in venous against capillary blood.

Materials and methods. The study enrolled 22 clinically healthy patients of both sexes who had their venous and capillary blood samples simultaneously collected in compliance with pre-analytical rules. The tests were performed within three hours of sample collection on the analyzer Roche Cobas e601. Mean values were calculated for all parameters using a 95% confidence interval based on bootstrap. Differences between paired values of venous and capillary blood parameters were calculated and expressed in relative units (%). Wilcoxon test and correlation analysis were used to compare dependent samples.

Results. A statistically significant increase in capillary against venous samples was shown for FT3 (mean deviation 3.11; p < 0.001), FT4 (3.89%, p < 0.001), TgAb (2.73%; p = 0.041) and TPOAb (6.75%; p < 0.001), and a decrease – for TSH (-4.3%; p < 0.001). A 5%-deviation is in most cases clinically insignificant for diagnosis and choosing a treatment. All the capillary blood parameters under study strongly correlate (r > 0.75) with the same parameters of the venous blood: r = 0.971 for FT3; r = 0.993 for FT4; r = 0.958 for TgAb; r = 0.836 for TPOAb; r = 0.995 for TSH.

Conclusions. Thus, FT3, FT4 and TSH can be determined in the capillary blood without affecting accuracy and precision of clinical evaluation, while for TgAb and TPOAb these deviations may be significant only when the results are in upper borderline values.

thyroid function tests, clinical laboratory services, comparative study, venous blood

1. De Benoist B. Iodine Status Worldwide. Geneva: Dept. of Nutrition for Health and Development, World Health Organization; 2004.

2. Karmisholt J, Andersen S, Laurberg P. Variation in thyroid function in subclinical hypothyroidism: importance of clinical follow-up and therapy. Eur J Endocrinol. 2011;164(3):317-323. doi: 10.1530/eje-10-1021.

3. Dayre McNally J, Matheson L, Sankaran K, Rosenberg A. Capillary blood sampling as an alternative to venipuncture in the assessment of serum 25 hydroxyvitamin D levels. J Steroid Biochem Mol Biol. 2008;112(1-3):164-168. doi: 10.1016/j.jsbmb.2008.08.006.

4. Гематологические анализаторы. Интерпретация анализа крови. Методические рекомендации от 21 марта 2007 г. № 2050-РХ [доступ от 24.07.2017]. Доступ по ссылке: http://www.ramld.ru/articles/files/hemanalizator.pdf. [Gematologicheskie analizatory. Interpretatsiya analiza krovi. Guidelines № 2050-RH on 21.03.2007 [access on 24.07.2017]. Available on http://www.ramld.ru/articles/files/hemanalizator.pdf (in Russ.)]

5. Bain BJ, Bates I, Laffan MA. Dacie and Lewis practical haematology. 12th ed. Elsevier Health Sciences, 2016. doi: 10.1016/c2014-0-01046-5.

6. Arkin CF, Bessman JD, Calam RR. Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture; Approved Standard. 5th ed. Clinical and Laboratory Standards Institute, 2003.

7. Kayiran S, Ozbek N, Turan M, Gurakan B. Significant differences between capillary and venous complete blood counts in the neonatal period. Clinical and Laboratory Haematology. 2003;25(1):9-16. doi: 10.1046/j.1365-2257.2003.00484.x.

8. Patel A, Wesley R, Leitman S, Bryant B. Capillary versus venous haemoglobin determination in the assessment of healthy blood donors. Vox Sang. 2013;104(4):317-323. doi: 10.1111/vox.12006.

9. Priya M, Mohan Anjana R, Pradeepa R, et al. Comparison of capillary whole blood versus venous plasma glucose estimations in screening for diabetes mellitus in epidemiological studies in developing countries. Diabetes Technol Ther. 2011;13(5):586-591. doi: 10.1089/dia.2010.0218.

10. Ольховик А.Ю., Садовников П.С., Васильев А.В., Денисов Д.Г. Сравнительная оценка показателей общеклинического исследования венозной и капиллярной крови. // Медлайн.Ру. – 2017. – Т. 18. – С. 113-122. [Olkhovik AY, Sadovnikov PS, Vasilev AV, Denisov DG. Comparative characteristics of the complete blood count of capillary and venous blood. Medline.Ru. 2017;18:113-122. (In Russ.)] [доступ от 24.07.2017]. Доступ по ссылке: http://medline.ru/public/art/tom18/art6.html.

11. Lenicek Krleza J, Dorotic A, Grzunov A, Maradin M. Capillary blood sampling: national recommendations on behalf of the Croatian Society of Medical Biochemistry and Laboratory Medicine. Biochem Med (Zagreb). 2015:335-358. doi: 10.11613/bm.2015.034.

12. Hammer О, Harper DAT, Ryan PD. PAST: Paleontological Statistics Software Package for Education and Data Analysis. Palaeontol Electronica. 2001;4:1-9.

13. RStudio Team. RStudio: Integrated Development for R. RStudio, Inc., Boston, MA. [доступ от 24.07.2017]. Доступ по ссылке: http://www.rstudio.com.

14. Jones MR, Cheek JM, Tamaki J, et al. Plasma amino acid concentrations in premature infants: effect of sampling site. Am J Clin Nutr. 1989;50(6):1389-1394.

15. 15. Webb N, Roberts D, Preziosi R, Keevil B. Fingerprick blood samples can be used to accurately measure tacrolimus levels by tandem mass spectrometry. Pediatr Transplant. 2005;9(6):729-733. doi: 10.1111/j.1399-3046.2005.00367.x.

16. Falch D. Clinical chemical analyses of serum obtained from capillary versus venous blood, using Microtainers and Vacutainers. Scand J Clin Lab Invest. 1981;41(1):59-62. doi: 10.3109/00365518109092015.

17. Fraser CG. Biological variation data for setting quality specifications. [доступ от 11.09.2017] Доступ по ссылке: https://www.westgard.com/guest12.htm