More insulin will be needed to allow the body to burn extra sugar for energy when the blood sugar is high. Usually only the Humalog or Regular insulin is increased. If the blood sugar is low, the short-acting insulin is not increased and may instead be reduced or omitted. Occasionally the blood sugar will be low but ketones will be present. The ketones form because the body needs extra energy and fat is broken down.
Ketones are a by-product of fat breakdown for energy.
In this case, you should eat and see if the ketones go away. Sometimes sugar popsicles will help. The best way to know how much insulin is needed is to have kept records from a previous similar illness and to know what insulin dose worked then. It is important and helpful to keep good records. If you do not know about previous illnesses, look at the present blood sugar levels.