Raisins would be very high in sugar but it may be in the form of fructose. Fructose does not raise blood sugar levels the same way glucose but instead goes directly to the liver to be processed. Many in the low carb community of doctors claim fructose is even worse than glucose and any excess that can not be burned by the body goes to liver fat leading to fatty liver. Raisins are just grapes times concentrated.

Table sugar (sucrose) is half glucose and half fructose.

John