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Testing For Hypoglycemia And How Your Doctor Can Help

By Dr George Samra, MB, BS (Sydney), FACNEM

The correct test for Reactive Hypoglycemia is a G.T.T. The test should be ordered by the doctor as follows: G.T.T. – 4 hours. All 1/2 hourly readings. No special diet prior.

The Glucose Tolerance Test is the classical test used in diagnosing Diabetes. The Diabetic test is a 2 hour G.T.T. with just 3 readings, the fasting, the 1 hour and the 2 hour. This test is not correct for testing Functional or Reactive Hypoglycemia. With Hypoglycemia one is interested in the full reactions to a sugar load. In both cases a 75gram load of glucose is given to the patient after having collected blood for the fasting level. With Reactive Hypoglycemia the emphasis in on the word “Reactive”- one is looking for the sugar reactive phenomenon in which the blood sugar either drops suddenly or falls very low. Part of diagnostic criteria for Hypoglycemia is the rate of fall of blood sugars, hence the relationship between consecutive readings is very important. Sudden drops in blood glucose will usually trigger an adrenaline response and subsequently adrenaline symptoms such as nervousness, shakiness, dry mouth, irritability, agitation, neck stiffness and sometimes palpitations or a racy heart.

With Reactive Hypoglycemia one is also seeking to ascertain how low the blood sugar may go as this in fact is one of the measures of severity. The brain is dependent on blood glucose as it’s only fuel supply under normal circumstances. When the blood glucose falls below a certain level, usually 3.6mm/L, there is a lack of available fuel to the brain and symptoms of brain starvation will occur – these include tiredness, moodiness, depression, forgetfulness, poor concentration and cloudy headedness.

The purpose of the G.T.T is to clarify how well one tolerates glucose and by doing it properly one is able to see if the blood sugars drop too rapidly or fall too low. It is important that the glucose tolerance test is done accurately and properly. The following rules apply:

1.    Fasting for at least 10 hour prior. Usually this means fasting from 10.00p.m. the previous night.

2.    Once the fasting sugar level has been collected. A 75gm glucose load is given to the patient. In children this may be adjusted according to their size, however usually a 50gm glucose load is suitable for the vast majority of children.

3.    The pathology lab should be made aware that we are not trying to diagnose Diabetes but rather Reactive Functional Hypoglycemia. For this reason the doctor is requesting a longer test, i.e. 4 hours instead of 2 hours as well as all 1/2 hourly readings.

Does Insulin Need to be Measured?
Usually Insulin levels do not need to be measured. However, when the doctor suspects an Insulinoma (Cancer of the head of the Pancreas) and also in the case of an obese patient insulin levels may prove very useful in clarifying the diagnosis.

Determination of the Glucose Tolerance Test Results
The different types of Hypoglycemia have been classified based on the Glucose Tolerance Test. If the blood glucose levels falls below 3.6mm/L (65mg per 100ml) then Absolute Hypoglycemia is present. If the blood glucose level drops rapidly i.e., greater than 1.6mm/L (30mg per 100ml) in 1/2 an hour or greater than 2.6mm/L (50mg per 100ml) in 1 hour, then Relative Hypoglycemia exists. If the curve has a sharp gradient and numbers below 3.6mm/L together, then is regarded as the classical Reactive Hypoglycemia. The lower the blood sugar readings and the larger the gradient the blood glucose falls the more severe is the diagnosis. A fasting Hypoglycemia alerts the doctor the possible diagnosis of Insulinoma. The flat curve response and its implications have also been described elsewhere on this web site.

See results of a GTT and here.


What to Say to Your Doctor & How to Approach Your Doctor
Most doctors have a problem understanding Reactive Hypoglycemia and this frustrates them. For this reason I’m including a letter to the doctor that you should download and which should help you get a satisfactory response from your doctor.


Web Site http://www.hypoglycemia.asn.au

Dear Doctor,

Your patient has identified with the many symptoms suffered by patients with Reactive or Functional Hypoglycemia. As you well know, Hypoglycemia is low blood sugar, however Reactive Hypoglycemia is a sugar reactive phenomenon (and is not Diabetes.) After a sugar load such as a soft drink or cake, patients with this condition often suffer symptoms due to a sudden drop in their blood sugars, which typically occurs between 1 1/2 hours and 2 1/2 hours after the sugar consumption. Typical symptoms of Hypoglycemia include tiredness, poor concentration, moodiness, depression, forgetfulness, nervousness and irritability.

The brain relies on glucose as its only fuel under normal circumstances. The symptoms of Hypoglycemia relate to the fact that the brain is not being fueled properly at some point in time. In order to investigate this condition and help your patient please order a Glucose Tolerance Test as follows:
GTT 4 Hours. All 1/2 Hourly Readings. No Special Diet Prior.

This is the correct way to order a test for Reactive Hypoglycemia. The patient is usually given a 75gm load of glucose soon after the fasting level has been collected. With the prolonged GTT and with the 1/2 hourly readings one is able to ascertain both the rate of fall of blood sugars as well as whether they in fact fall below the Hypoglycemia line that is usually 3.6 mm/L (65mg per 100ml). Guidelines for interpretation of the Glucose Tolerance Test are available on the web site or directly from the Hypoglycemic Health Association.

Thank you sincerely for your co-operation. This test may help to clarify many troublesome symptoms that your patient has been experiencing.


Yours sincerely,
The Hypoglycemic Health Association.


55 Responses

  1. Sherron says:

    I have taken the questionnaire and came out with a score of 16.

    The thing that has prompted me to this website is good old Dr Google after I had a minor “episode” tonight.

    Episode = During exercise or over exertion (a Netball game) I sometimes start getting the following symptoms in about this order: Fatigue, loss of breath, nausea, dizziness, loss of hearing and colour, cloudy head then black out.

    These episodes don’t occur frequently and have only ever got to the black out stage once or twice (for a second or 2). At first I thought it was from being unfit or that maybe I wasn’t eating enough but after improving my fitness and eating more regularly I was still getting episodes and was asked by my trainer to see a Doctor.
    Had a spirometery test, ECG, blood test and chest xray all which came back fine. Was sent off with an asthma pump (even though the spirometery test was fine) and a possible diagnosis of sports induced asthma (played sports my whole life and frequently so not the issue in my opinion).

    Like I said, the episodes happen too infrequently and although at one stage I had a cluster of them I could not put it down to diet as I was eating low GI and more protein at the time.

    Basically frustrated and wondering if I should do this test or re-examine diet??

  2. Nadia says:

    Dear Dr Samra,

    Do I need to perform this GTT test also if I have been experiencing Fasting Hypoglycemia?

    Many thanks,

  3. jur says:

    You have a choice of a questionnaire test of or a GTT, as explained at Testing for Hypoglycemia,

  4. Jarrod says:

    I scored 120 on the written NBI so obviously I may be suffering from hypoglycemia. I live in Canada, and can’t seem to find much info on getting the GTT done here. Do you think it is still necessary to take considering my high score on the NBI? Or is this a prudent test to take regardless in determining how to treat and deal with each individual’s case?

    Thanks so much! I am in much need of help.


  5. Dan says:

    Just come across this site after years of a living hell . I’m told I’m 2 people , most of the time I’m loving & caring then for no reason I have these horrid nasty outbursts which leave me drained . I often start to feel if as I am drunk . If I’m driving I could just pull over and sleep , losing all track of time . If at home , il sleep anywhere , oblivious to the world. Sometimes I just erupt over the stupidest thing with no reason to anything I’m saying , it’s like I’m possessed.
    I’ve been to the doctors many times. A few years back I’d start work at 8 , tea break was at 10-30 , if I didn’t drink a large bottle of fizzy drink then , I would be asleep , out like a light . That was the same at lunch . The doctors found nothing .
    Recently I went back to the Doctors because my outbursts are more frequent but they tested me for diabetes but that came back clear. Maybe they are looking for the wrong thing ?

  6. Theresa says:

    I am wondering if Doctors in Australia can order a 1/2 hour GTT. I asked a doctor a while back and she said they would only do it every hour.
    I am wondering if you know of a doctor in Adelaide who is open to this condition?

  7. Jackie Relaford says:

    I took your test for hypoglycemia and scored 25, the quiz was short so how conclusive is it?. I have a tremendous number of food intolerance’s including sugar, yeast, gluten, beef, oranges, dairy, eggs, basil, tuna, white potatoes, black pepper sardines, mackerel, cashews, walnuts and almonds so I eat whole food that I prepare myself.The results of an adrenal sufficiency test shows that I have high cortisol all day so sleeping is a challenge.I have been off the night shift and semi retired for 2 years but still can’t sleep.Is this enough information to make you think I should persue help from my doctor or should I go in another direction?

  8. Emma says:

    Does pregnancy effect the test?

    I got a flat response to a fgtt.. the standard 2hr one 3.7/3.9/3.5

    Should i be concerned and look at getting my thyroid tested?

    • jur says:

      A flat curve hypoglycemic response is usually a sign of hypothyroidism. Your question should be addressed to the doctor testing you for hypothyroidism,.

  9. Richard says:

    I recently had a glucose tolerance test : After fasting for 9 hours my results are as follows:
    Fasting (9 hours) 5.5
    1 hour after 75g sugar drink 13.3
    2 hours 5.4
    3 hours 3.4
    3 1/2 hours 4.5

    I wasn’t able to last until the 4th hour as I felt sick.
    Is this a diagnosis of hypoglycemia ?

  10. Amanda says:


    I am so glad I came across this site. I scored a 57 on that quiz. I have been to the doctors but they only seem to test for diabetes and my fasting level is in the normal range.

    After searching Dr Google I have come across reactive hypoglycemia and am wondering if this might be what is happening. As my episodes seem to be after I eat. I get most of the symptoms hungry shaky, irritable, brain fog and it all fixes as soon as I eat something. It seems like I can’t go more than 2 hours between meals. I have to eat something to avoid getting these episodes.

    I had a scary episode the other night when I couldn’t think clearly and then I almost had a panic attack and started to hyperventilate. Thankfully my husband was there to calm me down. I have also noticed that after I have a bad episode I feel exhausted for a few hours.

    That last episode made me go to the doctor again and he did blood tests. I go back to see them on Tuesday but they have said the results are not urgent.

    The thing that concerns me the most is I will be my completely normal self and then all of a sudden I am in a downward spiral.

    I was just wondering if you could give me any advice as how to discuss these things with the doctor.

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