Question: What would cause my blood sugar to go from 135 to 150 without eating anything?

Dr. Hibberd's Answer:
Diabetes is the loss of the body's self-regulation of glucose either through a disorder of insulin production (type 1) or the inability to use insulin produced by the body commonly described as insulin resistance (type 2).
Our cells require glucose to be regulated. Levels between 60 and 100 are ideal in order to function properly. Most cells, except for brain tissue, require insulin to absorb glucose. Prolonged elevations interfere with healing and have all kinds of adverse effects. There is also often little tolerance to levels below 50.
Disorders of glucose are not always caused by diabetes. Many body processes, aside from food consumption, will elevate blood glucose, especially stress. Since the answer to your question has several factors, it needs to be reviewed in the context of your existing diagnosed or undiagnosed medical conditions.
I recommend you have your doctor review your readings taken before meals and bedtime in addition to a selection of readings taken two hours after eating, and decide if a metabolic workup is needed.
Sometimes a Hemoglobin A1C is revealing, and occasionally we need to resort to stimulation studies such as a three-, five-, or six-hour glucose tolerance test to answer your question properly.
Further review of glucose regulation problems will often involve screening thyroid (TSH) studies and occasionally adrenal hormone investigation and suppression testing. Bear in mind that a degree of variation in blood sugar readings is expected, but wide fluctuations, or persistent symptomatic fluxing is not expected, and often should be investigated further.
Very wide fluxes of blood sugar with attendant low symptomatic blood sugars are seen with some tumors, especially insulinomas.