Blood Sugar and Insulin

This information explains high and low blood sugar levels and how to manage them.

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’s made by your pancreas, which is an organ located at the back of your abdomen (belly).

If your pancreas doesn’t 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 (hyperglycemia). This can happen 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 (a temperature of 100.4 °F (38 °C) or higher), an infection, or had recent surgery.

Managing your blood sugar levels with insulin

If other diabetes medications don’t control your blood sugar levels, you will need to take insulin. You can take insulin only by injection (shot). How much you need will depend on:

  • Your blood sugar level
  • Your diet
  • Your level of physical activity
  • 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 when you have high or low blood sugar levels.
  • Lets you know if you’re 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.

Controlling your blood sugar level

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. Limit 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 physical 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

High blood sugar (hyperglycemia)

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

Low blood sugar (hypoglycemia)

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

  • Sweating
  • Shakiness
  • Headaches
  • Feeling faint
  • A fast, forceful heartbeat
  • Weakness
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How to Treat Low Blood Sugar

If your blood sugar is below 70 mg/dL and you’re awake and alert, follow the rule of 15/15:

  • Take 15 grams of sugar.
  • Wait 15 minutes, then retest your blood sugar.

Take 15 grams of sugar

Choose 1 of these options:

  • Drink 4 ounces of fruit juice or regular soda (not diet soda)
  • Drink 8 ounces of milk
  • Eat 4 large marshmallows
  • Chew 6 to 8 Life Savers® (not mints)
  • Chew 3 to 4 large glucose tabs

Do not eat chocolate or cookies when your blood sugar is below 70 mg/dL.

Wait 15 minutes then retest your blood sugar

Retest your blood sugar 15 minutes after eating 15 grams of sugar.

If your blood sugar is still less than 70 mg/dL when you retest, take another 15 grams of sugar. Retest 15 minutes later. Keep doing this until your blood sugar rises to 70 mg/dL or more.

When your blood sugar rises to 70 mg/dL or more, eat half of a sandwich and drink 4 ounces of milk or juice. You can also have your 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 high or low blood sugar that don’t go away.
  • Have frequent episodes of high or low blood sugar.
  • Have a blood sugar level of 200 mg/dL or more.
  • Have a blood sugar level of 300 mg/dL twice in 1 day.
  • Have a blood sugar level of 70 mg/dL or less.
    • Before calling your doctor, follow the 15/15 rule for treating low blood sugar explained in the “How to Treat Low Blood Sugar” section of this resource. When your blood sugar is back to 70 mg/dL or higher, call your 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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