Blood Sugar Testing

Diagnosing Hypoglycemia

There are a variety of tests and approaches to diagnosing hypoglycemia. First and foremost, check with your healthcare professional to determine what approach will work best for you. Our goal is to inform you so you are better prepared to have an intelligent discussion with your team of health experts. These perspectives are from sources we trust, but again, they are not intended to replace any medical diagnosis and treatment plan.

Present & Future Testing Parameters

What is the Glucose Tolerance Test? 

(Excerpted from The Do’s and Don’ts of Hypoglycemia: An Everyday Guide to Low Blood Sugar)

So, you think you may have hypoglycemia. You have all the symptoms. After discussing it with your physician, he agrees to give you a glucose tolerance test (GTT) to confirm the diagnosis. A test for three or four hours is requested when diabetes is suspected, but a six-hour glucose tolerance test is, by far, the most reliable method to detect low blood sugar. The HSF has always recommended that you settle for nothing less than the six-hour GTT. However, for a different perspective please see the section titled “Ask The Experts” below for Dr. Baird’s response to the question of whether a patient should take a glucose tolerance test to confirm hypoglycemia.

The night before having the GTT, you will be asked to fast after your evening meal. You are to eat or drink nothing until the time of the test. When you arrive at the doctor’s office or laboratory, still fasting, a tube of blood will be drawn and you will be asked to give a urine specimen. Then you will be given a very sweet beverage called “Glucola” to drink. This drink contains a measured amount of glucose. Your blood will be drawn in 30 minutes and once again in one hour after drinking the Glucola. For each hour after that, you will give a blood sample until five or six hours have passed. A urine specimen is given each time your blood is drawn. Each tube of blood and each urine specimen are tested to determine the amount of glucose it contains. When the report is sent to your doctor, he or she will be looking for glucose levels above or below normal at any time during the test. During the test, you may start to sweat, get dizzy, weak or confused. If you experience these symptoms to the point of being extremely uncomfortable for you get a headache or your heart starts beating quickly, ask the doctor’s staff to draw your blood IMMEDIATELY. Any of those symptoms could be a sign that your blood sugar has dropped to a very low level, and you want your doctor to have the lowest readings possible. If you wait until the next hour, your blood sugar may go back up and your doctor will be deprived of information essential to making an accurate diagnosis.

The interpretation of the GTT is just as critical as its administration. Because individuals have different body chemistries, what is a normal drop or curve for one patient may not be for the next. Do not forget that laboratory tests are only aids to a diagnosis, not the final word. Remember, too, that the test is not for everyone. Children and the elderly, in particular, frequently require another method. Dr. Carlton Fredericks, author of Carlton Fredericks’ New Low Blood Sugar and You, frequently used “therapeutic diagnosis.” “This means putting the suspected hypoglycemic on the correct diet and watching the response. If, after a month or two, the symptoms are significantly reduced, the diagnosis has been established.” This procedure can be a less expensive, more convenient and less stressful method for diagnosing low blood sugar.

In conclusion, if you’ve read the basic facts about the glucose tolerance test, discussed it thoroughly with your physician and both of you have decided that this test is necessary, then read some of our suggested do’s and don’ts.


  • Do understand the purpose, procedure and instructions BEFORE you have the glucose tolerance test administered.
  • Do make sure the test is scheduled in the morning (no later than 9:00 a.m.).
  • Do ask the doctor or nurse to repeat instructions if you do not fully comprehend what you are or are not supposed to do.
  • Do tell your physician, if he/she is not aware, if you are on any kind of medication. Some medications may affect blood sugar levels.
  • Do use the “therapeutic diagnosis” for children and the elderly.
  • Do bring someone with you, especially if you are experiencing severe symptoms.
  • Do bring a book, newspaper or magazine of your choice to help overcome the boredom. Sitting five or six hours is not something we’re used to doing. Consequently, restlessness often sets in.
  • Do have a pen and paper available to write down all the symptoms you are experiencing and at what time.
  • Do bring a sweater with you. Very often, a patient will experience chills during the GTT. It is best to be prepared.
  • Do arrange beforehand to have someone pick you up if you go alone for the test. Sometimes, afterward, you may be weak and driving could be difficult.
  • Do bring a snack to eat immediately after the test, particularly if you must go home alone. Eating some protein (nuts, seeds, meat, cheese, etc.) will bring your blood sugar up, allowing you to feel good enough to get home safely.
  • Do set up an appointment before you leave to go over your test results.


  • Don’t demand a glucose tolerance test. It is not always necessary.
  • Don’t accept a three- or four-hour glucose tolerance test for diagnosing hypoglycemia.
  • Don’t demand to have the glucose tolerance test if you have a fever or infection. It could affect the test results.
  • Don’t be shortchanged. Go over the results of your GTT with your physician thoroughly.
  • Don’t be fooled by the terms “borderline” or “mild” in the case of hypoglycemia. Too often when patients hear these terms, they don’t take their diagnosis seriously. This could eventually cause grave consequences.
  • Don’t dismiss the fact that you may still be hypoglycemic even if the GTT doesn’t confirm the diagnosis. Laboratory tests are not always conclusive. The conditions under which the test is given may alter the results. The best rule to follow is: don’t treat the results of the test, treat the symptoms.

What the Experts Say

“I’ve read so much about the glucose tolerance test (GTT), but I’m more confused than ever. Should I take it to confirm that I have hypoglycemia?”

Doctors who have significant experience with blood sugar management disorders such as hypoglycemia are able to identify probable candidates for this diagnosis through symptoms, history and examination alone. Subjecting a patient to a glucose tolerance test can be very stressful, and many doctors opt not to do these tests for that reason. Additionally, the GTT may not provide enough information to establish the diagnosis, which could further confuse and complicate the situation.

A single finger prick seldom tells us enough to be of significant value. It is both the absolute level of blood sugar as well as the change in levels that assist us in making a diagnosis. Also, the standard glucose tolerance test, due to its lack of flexibility, is prone to error and can easily miss some of the low blood sugar readings and precipitous drops in glucose levels as the patient responds to a heavy glucose load.

If a patient’s symptoms warrant it, I use a different protocol for the GTT. This enhanced design remedies the shortcomings of the standard test and has, in practice, identified a higher percentage of patients with blood sugar management disorders. For the purposes of this test, the patient is instructed to eat a diet high in carbohydrates for three days prior to the test. On the day of the test, the patient is to fast from midnight on. Water is permissible. The first (venous blood, not finger stick) serves as a baseline for both blood glucose and serum C-peptide insulin. Insulin levels are monitored along with blood glucose measurements. The test proceeds according to the standard protocol until the patient begins to become symptomatic. With the onset of symptoms (falling or low blood sugar), blood samples are drawn every fifteen minutes and recorded until stabilizing around baseline level. At this time, the test can be terminated. At this point, the patient should eat something appropriate and should not be released from the examination center until they are perceived to be in control of their faculties. Any examination facility performing this testing should be equipped to manage hypoglycemia convulsions. If the fasting blood sugar level is in excess of 300mg/dl, the test should not be performed.

This test is considered positive for hypoglycemia if the rate of glucose drop is greater than 100 mg/dl/hr or an absolute blood sugar level is less than 60 mg/dl at any time during the test. Whether or not you should have a glucose tolerance test should be determined by you and your physician. -Dr. Douglas M. Baird

The study I conducted to support my doctoral dissertation (“Brain Neurophysiology in Persons with Reactive Hypoglycemia”) using the EEG evolved from the experience I had at Stanford University hospital at the time I was going through the six hour glucose tolerance test. At about the fourth hour I passed out and luckily was with Dr. Bill Hudspeth (now deceased) my primary professor and coauthor. My glucose tolerance test came back normal! No one had monitored my behavioral changes and concluded I was just fine. Dr. Hudspeth and I knew at the time that other patients were not being properly diagnosed, just like me.

Currently many physicians only run fasting blood sugar which tells us nothing about the course of this disorder. As you know from the dissertation, there is a pattern of EEG response in the person with hypoglycemia, some more serious than others, that does not always correlate with the glucose tolerance test. Our most disturbed patient, who had recently run her car off a mountain road, showed spikes on the EEG. This young woman had been hospitalized in a mental institution at 18 years of age. She was diagnosed in our program and with proper diet and support she functions perfectly now as a prominent attorney telling everyone about her missed diagnosis: hypoglycemia!

The point is that the glucose tolerance test is not adequate by itself and the person should be monitored for behavioral changes and if possible the EEG!

Linda Peterson, PhD, RN, MSN, MFT

Dr. Linda Peterson

Glucose Control Parameters + Insulin Levels

This gets technical – again, rely on your own healthcare provider for advice. However, this information may be useful to some healthcare professionals.

Every doctor gets a fasting glucose on all their adult patients, looking for type 2 diabetes. This can be the worst parameter to measure, because it is the last thing to change; by the time the glucose has changed, the horse it out of the barn. By the time the fasting glucose rises over 100 mg/dl (signifying glucose intolerance; 126 means diabetes), metabolic syndrome is in full force, and there’s no options for prevention anymore; now you’re in full-fledged treatment mode. The same is true for hemoglobin A1c (HbA1c), the blood test that assesses glucose control over the preceding 3 months.  By everyone’s estimation, under 5.5% is normal, while over 6.5% is frank type 2 diabetes. It’s what goes on in between that is up for grabs, and it’s in this gray zone where most adults live.

The body will do everything it can to maintain the serum glucose in the normal range, including increasing the insulin (that’s insulin resistance). So, the way to interpret a fasting glucose is by getting a simultaneous fasting insulin level, which tells you how hard the pancreas is working. A fasting insulin of greater than 20 microunits/ml usually means significant insulin resistance, and risk for metabolic disease.

From the glucose and insulin levels together, you can calculate an index called the Homeostatic Model of Insulin Resistance (HOMA-IR), which assesses your risk for diabetes. “Incorporating fasting insulin and especially insulin assay after an OGTT as enhanced screening methods may help to increase the ability to detect diabetes and pre-diabetes, allowing earlier intervention to prevent diabetic complications.” (reference: A HOMA-IR of less than 2.5 is excellent, and 4.3 is good. Anything higher can mean trouble.

However, many academic societies (including the American Diabetes Association) do not advocate getting a fasting insulin level. They have many reasons for arguing against it; such as cost, reproducibility, and the fact that fasting insulin does not correlate with BMI. But that’s exactly the point. There are two insulin disorders associated with obesity. A fasting insulin will only tell you about insulin resistance. It won’t tell you about insulin hypersecretion — in order to find that you have to stimulate the beta-cell (see below). And most doctors don’t know about insulin hypersecretion because they’ve never looked for it.

If you’re obese, there is a very high chance that you’re either insulin resistant, an insulin hypersecretor, or both at the same time. And since rational treatment is dependent on the pathology, some healthcare professionals are quick to perform the Oral Glucose Tolerance Test (OGTT). From these data it is possible to compute indices of insulin secretion and resistance, which will help determine what therapy or therapies might work best for each patient.

Ultimately, these tests and their analysis should be left to your physician. But you should know what they mean, as they are important for gauging your health.  Unfortunately, some doctors are reluctant to order such tests, especially as a preventative measure.


New Tech + Old School

Continuous Glucose Monitoring is an emerging technology that has great potential to transform diagnoses of hypoglycemia – matched with good old fashioned food journaling. These bio-monitoring devices are currently not currently approved by the FDA for indications beyond type 1 diabetes, so the companies that make them are not allowed to promote or suggest consumers use them for conditions such as hypoglycemia – however, doctors can and do use the devices for “off-market” applications. Unfortunately the cost of these devices is not currently covered under most insurance policies, and will be out of pocket for the patient, or built into the general cost of services provided by the healthcare provider, if they choose to use the devices.  We do believe this technology has the potential to be a huge game changer for folks suffering from reactive / functional hypoglycemia, and we are optimistic that the indications will expand (along with health care coverage) in the near future.

Heart Monitoring Devices are also emerging as one of the potential tools for monitoring and preventing hypoglycemia.

The HSF is working with some of the innovators exploring the use of bio-monitoring devices for diagnosing and treating hypoglycemia, and we will report on our efforts as these exciting options are employed on behalf of those who suffer needlessly from blood sugar dysregulation.

Empower Yourself!

  1. Educate yourself about blood sugar and insulin response.
  2. Collect and organize information on your condition, symptoms, dietary habits, and blood/medical tests.
  3. Apply and commit to a defined course of treatment, including lifestyle changes.
  4. Seek healthcare providers knowledgeable about hypoglycemia or be prepared to get second opinions.
Have our seen our Hypoglycemia Infographic?

Check it out – it provides a great overview to low blood sugar and what you can do about it!

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