48 Hour Fast

Why am I having this test?

• The test is used to determine whether your blood sugar (glucose) becomes abnormally low when you are fasting (going without food).
• The test can diagnose or exclude an Insulinoma which is an abnormal insulin levels produced by a tumour.

How long will I be in hospital?

• You will be in hospital for 2 days e.g. Tuesday morning to Thursday afternoon.
• You may wish to bring a book, magazine or activity with you.

Who carries out this test?

A nurse who specialises in endocrinology is responsible for carrying out this test.

Where is the test carried out?

• You will be sent a letter with details of the test and which department you will need to attend
• You will be admitted to a ward when a bed becomes available, at this point the 48 hour fast will start.

What do I need to do on the day of the test?

• You need to have a light breakfast such as tea and toast between 7.00am and 8.00am on the day of admission.
• Please take all your medication as usual.
• Please bring all your medication into hospital with you.

What happens during the test?

• On arrival you will meet the nurse who is responsible for the test. The nurse will explain the test and you will be given the opportunity to ask questions prior to the start of the test.
• The test will not commence until a bed becomes available.
• Throughout the test you can only drink water. The water may be tap water or bottled water, either still or carbonated, as long as it is sugar free. Flavoured water is not allowed.
• A routine blood sample will be taken from a vein in your arm on each day during your stay in hospital.
• You will have a blood sugar test taken 4 times, this is where we will prick your finger with a needle, at various times during the day.
• If you feel dizzy, cold and clammy or feel generally unwell at any time, you should inform the nursing staff and they will check your blood sugar again.
• If the result is very low, a doctor or the nurse will take further blood samples.
• Once these results are confirmed the fast will be discontinued and you will be given food and fluids until your blood sugar level is back to normal. The doctor or nurse will make this decision to stop the test.
• During the test, if your blood tests do not show any low blood sugar levels the test will continue for the full 48 hours.
• You should remain active and walk around the ward during the test as much as you feel able.
• At the end of your 48 hour fast a final blood test will be taken. You will need to wait for these results before you are given any food.
• On completion of the test you will be safe to resume your normal daily activities.

Are there any side effects?

• You may feel hungry, off colour and generally tired and weak during the investigation.
• You may experience a headache during the test. Please inform the nursing staff, as simple painkillers may be used.

What happens after the test?

The results will be discussed at your next clinic visit or a letter will be sent to you and your GP. The nurse looking after you will arrange a further appointment as required.

If you require more details please contact the Specialist Nurses in Endocrinology:
Tel: 01274 382019 Monday – Friday between 8.00am and 4.00pm except Bank Holidays