We select the number of tubes for each finger-prick test based on 3 things: how many markers are being measured, how "thirsty" some of those markers are (meaning you need a lot of blood to measure them), and what is the failure rate (e.g. insufficient sample) of the test if we try to measure too many markers from just 1 tube of blood. The Thyroid Check UltraVit is a really borderline test in that it can be completed on a single vial of blood but only if you fill the tube right to the top line (i.e. a perfect fill). If you don't achieve a full sample then there is a high probability that we won't be able to test all the markers due to insufficient sample. We believe that it is a much better customer experience to collect a bit more blood at the outset and receive a full set of results than to only fill 1 tube and receive only partial results.
If you are confident that you can fill the vial sufficiently, then you are welcome to do a Thyroid Check UltraVit on 1 tube, but for the best and most reliable experience we recommend 2.