Help me understand this glucose tolerance test result

November 9, 2008 5:40 PM

Can you help me interpret this glucose tolerance test result?

I am trying to make sense of what this (hypothetical) glucose tolerance test result means.

(1) Does this result (view test result here) support a claim that the subject is suffering from hypoglycemia?

(2) What does the first row (in which "fasting" appears) mean? What is the significance of the 91 mg/dL on that row and the reference range on that row?

(3) Any idea why "(low)" appears on the last three rows?

(4) If you have the expertise to interpret this result, what does it mean to you in layperson's terms?

Please assume I know absolutely nothing about medicine. To anyone inclined to say "go see your doctor" --- this is a hypothetical result and nobody's health or medical treatment depends upon the answer to this question. Thanks!

posted by jayder to health & fitness (15 comments total)

Fasting means that the person taking the test hasn't eaten for at least 8 hours before the test was taken. The reference range is just that, the blood sugar should be within that range after a fast.

Low means that the blood glucose level is lower than a normal level for one, two, and three hours after eating.
posted by sugarfish at 5:46 PM on November 9, 2008

Yes, what sugarfish said.

The first result, 91 mg/dL is a pretty normal fasting blood glucose, in my experience.

The next three numbers occur after the person has been given a fixed dose of glucose (you probably knew that, but you said not to assume, so...) and normally the blood glucose levels would rise during the 1 hour interval, then go back down -- as the reference ranges would suggest.

To interpret this result, it does look kind of like postprandial hypoglycemia (low blood sugar following eating.) Having a blood sugar at those last two levels would be low enough to cause symptoms of hypoglycemia for most people.
posted by peggynature at 5:53 PM on November 9, 2008

(That is, assuming I've converted the numbers correctly, because I normally work with mmol/L, not mg/dL!)
posted by peggynature at 5:54 PM on November 9, 2008

peggynature is right. And having a glucose in the 40s would almost certainly cause symptoms like shaking, weakness, and confusion, unless the person had hypoglycemia unawareness.
posted by chinston at 6:04 PM on November 9, 2008

The next three numbers occur after the person has been given a fixed dose of glucose (you probably knew that, but you said not to assume, so...)

No, I didn't know that (I was serious when I said I know nothing!). Do you mean that when these tests are administered, the subject is given an hourly dose of glucose?

it does look kind of like postprandial hypoglycemia (low blood sugar following eating.)

Why do you say "following eating"?

Thanks for all the answers so far.
posted by jayder at 6:04 PM on November 9, 2008

And having a glucose in the 40s would almost certainly cause symptoms like shaking, weakness, and confusion, unless the person had hypoglycemia unawareness.

So, is it the case that an "ordinary" person fasting according to this schedule would not have glucose as low as this test result indicates?
posted by jayder at 6:06 PM on November 9, 2008

Do you mean that when these tests are administered, the subject is given an hourly dose of glucose?

The test works by giving a single dose of glucose to the subject, then measuring the subject's blood glucose levels at fixed time intervals after (1, 2, 3 hours). Generally 1 hour after the dose, the body might still be processing the glucose so it would show up in the blood (which is why the normal range is higher then), but by 2 or 3 hours the body will have returned to fasting levels. Generally.
posted by chinston at 6:08 PM on November 9, 2008

What suggests is that the fasting (ie empty stomach) blood glucose level is within the "normal" range. The values at 1, 2, and 3 hours are the blood glucose level at each time point following a challenge with glucose. In other words the person has been given a set amount of sugar orally and the blood levels are checked at the time intervals. It says "low" because the blood glucose levels the glucose challenge are lower than the reference ranges on the right.

In layman's terms, on an empty stomach this person appeared to have relatively normal blood sugar levels, but developed a significant drop in blood sugar after the equivalent of a meal.
posted by drpynchon at 6:08 PM on November 9, 2008

So, is it the case that an "ordinary" person fasting according to this schedule would not have glucose as low as this test result indicates?

Correct. That would be very odd and cause for alarm.
posted by chinston at 6:09 PM on November 9, 2008

So, is it the case that an "ordinary" person fasting according to this schedule would not have glucose as low as this test result indicates?

For an insulin-dependent diabetic, you'd see these results if you took too much insulin at mealtime, thus depressing your blood-glucose levels an hour or two after eating. Then you'd have to get some sugar to bring your levels back up.
posted by chinston at 6:10 PM on November 9, 2008

Why do you say "following eating"?

Just because the one dose of glucose given for the test sort of mimics the person eating a meal containing carbohydrate. This test is a way to find out how someone's body handles carbohydrate, essentially.

I would only expect to see this in someone with diabetes who took too much insulin just before the meal (or glucose dose), like chinston says. Or maybe in someone with diabetes who takes an insulin secretagogue like Glyburide, which can cause hypoglycemia. Anyhow. Some people do swear there is such a thing as reactive hypoglycemia in people who don't have diabetes, where they get low blood sugar after eating. But who knows.

Either way, these test results are not normal.
posted by peggynature at 6:26 PM on November 9, 2008

The GTT result that you posted would indicate to me an excessive production of insulin by the pancreas post 100 or 75 mg glucose challenge. I do not diagnosis since I am not a doctor, only a tech, but this is an abnormal GTT that might indicate hypoglycemia. If the patient is pregant it could be gestational.
posted by bjgeiger at 6:49 PM on November 9, 2008

This is a really good question, and I'm glad you asked about it.
Hypothetically, if a person wondered about this, would it be useful to ask the doctor about getting a glucometer and track this for little while. Would that be helpful diagnostically? (Either with or without the glocose tolerance test?)
posted by unrepentanthippie at 7:43 PM on November 9, 2008

unrepentanthippie: it might be useful if you got a BG monitor, tested yourself first thing in the morning before eating, and then an hour or two after each meal, maybe also keeping accurate track of your food intake through the day. This can be really complicated, burdensome, and tricky to do.

The most important thing would be to then bring those records and logs to your doctor to have them corrently interpreted -- I'm not sure if a GP would be all enthusiastic about that, as it's labour-intensive. Maybe they'd send you to an endocrinologist who'd be willing, if the results seemed really abnormal. They'd still probably want to do the OGTT, and maybe test your HbA1c before foisting you off on a specialist, because people's home meters and logs can be inaccurate.

However -- if you did bring in really detailed logs showing a consistent pattern of hypoglycemia after eating to an endocrinologist, I'm sure they'd sit up and take notice -- though s/he may still want to do further testing.

(This is all just in my observation from working in a diabetes clinic. YMMV of course.)
posted by peggynature at 6:17 AM on November 10, 2008 [1 favorite]

peggynature

Perfect answer; that's exactly what I was looking for. In this case, I'm wondering about reactive hypoglycemia or that "insulin resistant" thing, which I gather may or may not exist, depending on the opinion. (The i'net is so full of misinformation I can't tell.)

This is supposed to be a common issue with people who have autoimmune issues and I've got several of them, all related. I have been assured repeatedly I do not have diabetes. The problem I'm wondering about is that every time I eat, I fall asleep an hour later. Oddly enough, Mom has the same issue, with sugar only. She's mid 80s. All I had in mind was tracking it for a little while to see if I could find a correlation or not.

I had glucose tolerance about 20 years ago and got really shocky so they discontinued the test after about 3 hours if I remember that right. My last HbA1c is about 2 months old and fine, and I usually get it done annually. I have an appointment with the endocrinologist in a week, albeit for other issues (malabsorption). I know it's a long shot and not likely. I can keep reasonably decent records, and I am aware that most home meters are not going to be deadly accurate, probably lucky if it's close. My PCP is a concierge physician so he won't mind looking at it.

Thanks again so much for the information. That's very helpful and deeply appreciated.
posted by unrepentanthippie at 9:54 AM on November 11, 2008