Without taking insulin, Carlos is at risk of developing diabetic ketoacidosis which can be life threatening.

This is because:

(1) The high levels of glucose in his blood are causing him to urinate a lot, which is leading to dehydration.

(2) His cells are not getting the glucose that they need to work properly.

As you can see from the picture of Carlos, he is slim.

This is because without insulin, the body is not very good at laying down fat or muscle.