Sounds like a great opportunity to value add. You might want to...

Sounds like a great opportunity to value add. You might want to also consider measuring C-peptide. It is produced in equimolar amounts to insulin, but is specific to the ability to secrete insulin from their pancreas and is less likely to be degraded by the liver.

This would be important if some of the patients were on insulin therapy. In this case you wouldn't know if the insulin you measure in the blood is what they have produced from their pancreas, or what they have injected.

Measuring C-peptide in addition to insulin better compliments preclinical work looking at insulin secretion.

More opportunities for low hanging fruit could be getting to the patients to monitor their drug intake. If they have to take less diabetes medication or less blood pressure medication for example, that also bodes well for the intervention.

If you really wanted to get some valuable data in relation to diabetes outcomes, you could get them to wear a continuous glucose monitor. It's no extra burden for the participant really, they are even waterproof, and you get free-living data.