Fig. 1

Thyroid peroxidase autoantibodies (TPO-Ab) are detectable by enzyme-linked immunoassay in 3-mm punches taken from dried blood spot samples. Washed red blood cells were spiked with Liquichek Speciality Immunoassy Control (levels 1, 2, or 3) and then dropped on Whatman 903 Protein Saver filter paper cards. Cards were dried for 4 h and then frozen at − 80 °C. Levels of TPO-Ab in one 3-mm punch taken from these cards were quantified using the Accubind anti-thyroid peroxidase test system (Cat.#1125-300, Monobind Inc.). RBCs, red blood cells; L1, L2, L3; levels 1, 2, and 3 of the Liquichek Speciality Immunoassy Control, respectively