Fig. 2

a Stability of thyroid peroxidase autoantibodies (TPO-Ab) concentrations in response to storage over time at different temperatures. Venous DBS (vDBS) samples from four individuals were stored at − 28 °C, at room temperature (RT, ~22 °C), and at 37 °C for 28 days. On days 2, 7, 14, and 28 of storage, samples were transferred to − 80 °C. TPO-Ab concentrations in these samples were compared to those in samples stored at − 80 °C after collection and thawed only once for this experiment. The average percentage recovery for all four samples at the various timepoints for the three different storage temperatures is shown. Error bars are standard errors of the mean. Dotted lines indicate 80 and 120% recovery. b Stability of TPO-Ab concentrations in response to the number of freeze-thaw cycles. vDBS samples from six individuals were stored at − 28 °C and then allowed to thaw at RT for 2 h two, four, eight, or twelve times (each on separate days) after which they were returned to the − 28 °C freezer. These samples were then thawed one final time to assay TPO-Ab concentrations, for a total number of freeze-thaw cycles of 3, 5, 8, 9, and 13, respectively. TPO-Ab concentrations in these samples were compared to those in samples stored at − 80 °C after collected and thawed only once for this experiment. Dotted lines indicate 80 and 120% recovery