The absolute measurements of the blood vessels in children will always increase over time, as their body grows. As you know,
the z-score is what is tracked. However, if it has gone from 2.6 cm to 2.86 cm in 1 year, assuming that his bodily growth is normal, that is not much of a significant change (2-3 mm), so the z-score will likely be similar. This is far from needing an intervention.