Blood Sugar and Insulin

This information explains high and low blood sugar and how to take insulin.

About Blood Sugar and Insulin

Your body uses a sugar called “glucose” for energy. Glucose comes from the food that you eat. Your blood carries glucose to your cells so that your cells can use it for energy.

Insulin is a hormone that helps transport sugar from your blood into your other cells. It is made by your pancreas, which is an organ located at the back of your abdomen (belly).

If your pancreas does not make enough insulin, your blood sugar levels will rise above normal. This happens because the sugar stays in your blood instead of going into your cells. This is called high blood sugar or hyperglycemia. It can occur if you:

  • Have type 1 or type 2 diabetes mellitus.
  • Have had part or all of your pancreas removed.
  • Take steroids like prednisone or dexamethasone (Decadron®).
  • Have a fever, an infection, or have had recent surgery.

Managing your blood sugar levels with insulin

If other diabetes medications do not control your blood sugar levels, you will need to take insulin. You can take insulin only by injection. How much you need will depend on:

  • Your blood sugar level
  • Your diet
  • Your activity level
  • Your overall health
  • Other medications you take such as steroids

Measuring your blood sugar level

You can check your blood sugar level at home using a blood sugar meter. Your blood sugar target numbers are set by your doctor or diabetes educator. You will have targets for fasting and for other times during the day. Monitoring your blood sugar:

  • Alerts you to high or low blood sugar levels.
  • Lets you know if you are within your target range.
  • Helps you and your doctor decide how much insulin you need to bring your blood sugar within the target range.

You should write down all of your blood sugar results and doses of insulin in a log book, paper record, or a smartphone application.

You will be in charge of controlling your blood sugar levels. You should:

  • Eat a healthy diet, making sure to stay on your meal plan. Restrict the amount of sweet foods you eat.
  • Drink 6 to 8 (8-ounce) glasses of water or diet, decaffeinated liquids each day. You should do this unless your doctor or nurse gives you other instructions.
  • Increase your activity to the level recommended by your doctor or nurse.
  • Check your blood sugar levels as recommended by your doctor or nurse
  • Take your diabetes medication or insulin as prescribed by your doctor or nurse, Double check the dose before you inject the insulin.
  • See your doctor or nurse as directed.

We recommend that you get a MedicAlert® ID. It should say that you have diabetes and the type of insulin you take. For more information, call 888-633-4298 or visit


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Symptoms of Low and High Blood Sugar Levels

Hyperglycemia (high blood sugar)

This happens when you have a blood sugar level above your target range. High blood sugar can cause many symptoms, such as:

  • Being very thirsty or having a dry mouth
  • A need to urinate often, especially at night
  • Being very hungry
  • Having blurry vision
  • Drowsiness, fatigue, or tiredness

Hypoglycemia (low blood sugar)

This happens when you have a blood sugar level below 70 mg/dL. Low blood sugar can cause many symptoms, such as:

  • Sweating
  • Shakiness
  • Headaches
  • Feeling faint
  • A fast, forceful heartbeat
  • Weakness

If your blood sugar level is less than 70 mg/dL, follow the rule of 15/15. The rule of 15/15 is as follows:

  • Take 15 grams of sugar. This is equal to 4 ounces of juice, 8 ounces of milk, or 4 large glucose tablets. Do not eat chocolate or cookies.
  • Wait 15 minutes and retest your blood sugar.
  • If your blood sugar is still less than 70 mg/dL, take another 15 grams of sugar. Wait 15 minutes and retest. Do this until your blood sugar rises above 70 mg/dL.
  • When your blood sugar rises to 70 mg/dL or above, eat half of a sandwich and drink 4 ounces of milk or juice. You can also have your scheduled meal instead.
  • Your insulin or diabetes medication may need to be changed. Call your doctor or nurse to discuss this.
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Call Your Doctor Or Nurse If You:

  • Have a temperature of 100.4 °F (38 °C) or higher
  • Have chills
  • Have burning or pain when you urinate
  • Take steroid medications that are being increased, reduced, or stopped
  • Have signs of hypoglycemia or hyperglycemia that do not go away
  • Have frequent episodes of hypoglycemia or hyperglycemia
  • Have blood glucose readings of 400 mg/dL or more
  • Have blood glucose readings of 70 mg/dL or less. However, before doing so, follow 15/15 rule for treating low blood sugar described above. When your blood sugar is back to 70 mg/dL or above, then you should call the doctor or nurse.
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Insulin Action Guide

These are commonly used insulins at Memorial Sloan Kettering (MSK).






Rapid acting

Aspart (NovoLog®)

5 to 15 min

30 to 60 min

3 to 4 hours

Lispro (Humalog®)

5 to 15 min

60 to 90 min

3 to 4 hours

Fast acting

Novolin® R Regular

30 to 60 min

2 to 5 hours

6 to 8 hrs

Humulin® R Regular

30 to 60 min

2 to 4 hours

6 to 8 hours

Intermediate acting

Novolin® N (NPH)

1 to 2 hours

6 to 12 hours

12 to 14 hours

Humulin® N (NPH)

1 to 2 hours

6 to 12 hours

12 to 16 hours

Long acting

Glargine (Lantus®)

1 to 2 hours

No peak

Up to 24 hours

Detemir (Levemir®)
1 to 2 injections daily

1 to 2 hours

No peak

Up to 24 hours

Combination fast and
intermediate acting

NovoLog® Mix 70/30 (N/Aspart)

30 min

1 to 12 hours

5 to 18 hours

Novolin® 70/30 (N+R)

30 to 60 min

4 to 12 hours

14 to 16 hours

Humalog® Mix 75/25TM (N/Lispro)

5 to 15 min

1 to 12 hours

14 to 18 hours

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