by EBSCO Medical Review Board

Health problems can happen when blood glucose levels are out of the normal range. Having all advised exams and tests can help find problems early and treat them.

Problems that may happen include:


Hypoglycemia is low blood sugar. It can be caused by:

  • Taking too much insulin for the amount of food that was eaten
  • Taking too much insulin to treat "fasting" blood sugar
  • Skipping a meal or eating a smaller meal without lowering the insulin dose
  • Exercising harder or longer than normal without lowering the insulin dose


Hyperglycemia is high blood sugar. It happens when a person does not have enough insulin to remove the glucose in the body. It can be caused by:

  • Taking too little insulin for the food that was eaten
  • Eating without taking any insulin
  • Eating a larger meal without changing the insulin dose
  • Exercising more or less than planned without changing the insulin dose
  • Stress from being sick or life events (insulin dose may need to be changed)

Diabetic Ketoacidosis

People with type 1 diabetes can get ketoacidosis. This happens when the body is not getting enough insulin. Sugar cannot get into cells to make energy. The body starts breaking down stored fat for energy. When the fat breaks down acids called ketone bodies are left over. They can build up in the blood and can cause ketoacidosis. It is caused by the same reasons as hyperglycemia. It may also be caused by taking too little insulin when sick with an infection.

Diabetic Diseases of the Eyes, Kidneys, and Nerves

These diabetic diseases may happen:

  • Diabetic retinopathy can happen when high blood sugar and blood pressure harm tiny blood vessels in the retina of the eye. Other eye problems are also more common, such as cataract and glaucoma. A cataract is a cloud in the eye's lens that makes it hard to see. Glaucoma is an increase in eye pressure that harms the nerve that links the brain to the eye.
  • Diabetic nephropathy is kidney damage that can happen with diabetes. Blood passes through small filters in the kidneys. Diabetes can cause changes in the blood vessels that harm these filters. The filters then cannot clean the blood. Protein from the blood can leak into the urine. It can get worse over time. The kidney damage can lead to kidney failure.
  • Diabetic neuropathy is harm to the nerves. Having high blood sugar for many years can harm the blood vessels that bring oxygen to nerves. It can also harm the nerve's covering. Damaged nerves may:
  • Stop sending messages to the brain
  • Send messages too slowly
  • Send messages at the wrong times
  • This can make it hard for a person to feel pain, heat, and cold. It can also make it harder for blood to flow. A person could injure their foot and not know it. In some people, nerve damage can lead to foot and leg amputations.

Heart Disease and Stroke

Diabetes can cause cholesterol levels to rise. This leads to clogged arteries that make it hard for the blood to carry oxygen to the body. This can lead to:


American Diabetes Association. Standards of medical care in diabetes-2019. Diabetes Care. 2019; 42 (Suppl 1): S1-193.

Diabetes mellitus type 1. EBSCO DynaMed website. Available at: Accessed May 2, 2022.

Type 1 diabetes. American Diabetes Association website. Available at: Accessed May 2, 2022.

Revision Information

  • Reviewer: EBSCO Medical Review Board James P. Cornell, MD
  • Review Date: 03/2022
  • Update Date: 05/02/2022