Abnormal OGTT Results - The many causes

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As often happens, when looking for something a bit more specific, I came across this image at right, which led me to this webpage:  Laboratory Testing for Diabetes Mellitus.

Curve 1 is a normal OGTT, Curve 6 is a diabetic.  The other causes are listed:

  • Hypercorticism - curve 5.
  • Acromegaly - between curves 4 and 5
  • Hyperthyroidism - curve 4.
  • Pheochromacytoma (or "emotional hyperglycemia") - between curves 4 and 5

Pathologic conditions causing flat or depressed glucose tolerance results:
  • Insulinoma - Curve 2 or even more depressed
  • Intestinal malabsorption - curve 2 or even less of an increase
  • Low renal Tm for glucose reabsorption - may be normal curve 1 or may be depressed as in curve 3
  • Hypothyroidism - curve 2.
The cite contains a descriptive of each condition.  I'm mostly presenting this as an FYI.  One thing I was surprised by was the hypothyroid which delays the glucose absorption for a later peak with albeit suppressed glucose levels.  Couple hypothyroid with impaired pancreatic function and what do you get?  I don't know the answer to this, but can envision that there are a number of people in the community who might have "glucose intolerance" due to a mismatch between absorption, signaling and secretion. 


ProudDaddy said…
Any knowledge re reactive hypoglycemia (my assumed IFG problem when serum glucose dropped to below 50 at the 3 hour point of a 75 g OGTT)?
CarbSane said…
Were you at one point hyperinsulinemic by any chance?
Mario Iwakura said…
Hi Evelyn!

I don't know the other conditions (except hyperthyroidism), but definitely the hypothyroid curve is not correct. See, for example (in this study none of the subjects was receiving any treatment
or had a family history of type 2 diabetes):

ProudDaddy said…
Don't know. Only test ever was fasting insulin which was high normal, expected in relation to high normal, dawn effect, fasting glucose.
Craig said…
Any idea what the prevalence of these conditions is relative to 'classic' T2 diabetes?

Is there any reason to believe that a rise in the prevalence of these non classic cases is related to the diabetes epidemic?
CarbSane said…
The reason I asked is that in some GBP's who have glucose regulation restored end up with RH when they lose the weight. It's like their pancreas still overproduces.

I think it would be best that all OGTT's include insulin levels as well.
CarbSane said…
Hey Mario! Yeah, your paper does counter that curve, which brings all of this into question :( The bio http://pro2services.com/ leads me to believe this is from an online text of sorts written by a clinical chemist -- presumably from his experience? Perhaps selective interpretation of results or "conventional wisdom" -- according to this (1971) paper http://gut.bmj.com/content/12/2/172.full.pdf (bottom of pg. 3 of the pdf) they talk about the general thought but not science to back it up.

That is a very interesting paper on thyroid and IR, as this is true peripheral IR as we think of it -- e.g. impaired glucose clearance due to reduced transporters/rate.

It's not practical, but a radiolabel OGTT w/insulin levels would be far better to tease out the underlying pathologies.
lucy said…
Thanks Evelyn. This is very interesting. I am so confused with this blood sugar thing. I have been diagnosed borderline diabetic several years ago and have struggled with a LC diet over the years because of the BS thing. My story is similar to yours weight-wise and we are around the same age. My fasting levels range from 115 to 135. The 115 would be if I have been following a strick LC diet. I have always had high morning fasting readings. Two hour post meal readings range from 95 to 138ish. If I am a severe LCer or IFer I can get a reading of high 80s occasionally. I don't see myself on the chart above. Am I normal? Any thoughts?
ProudDaddy said…
My abnormal OGTT was a decade ago when I was overweight. Don't know if they include insulin in today's OGTTs. I brought this up because my curve obviously wasn't like any in the article, and I don't believe I'm the only person who has had episodes of hypoglycemia.

My OGTT confirmed that a high carb diet is not the best thing for me. By moderating my carb input, I've completely eliminated bouts of "weak and dizzy". Where is Nigel when you need him? (We are all different.)

Here's my point. Studies usually report averages. Statistical "significance" only predicts that the next similar study's average wouldn't likely differ by much. I tire of the "X diet is the only one for everybody" advice found in both the blogosphere and doctor's offices.
Karen said…
lucy a fasting level of 135-2x at a drs office would diagnose you as diabetic. when I was diagnosed I was 128 the first time after a couple of days of not eating much and 136 the next time after we got that cleared up and I had eaten normally. If you get a 200 - 2x when testing randomly you would be diagnosed diabetic too. But with your pp readings they look good. Something is going on at night. bloodsugar101.com (sorry Ev!) can give you some answers. Its a great site tho the 140 may be wrong it gives a person an idea what to do. Good luck!
CarbSane said…
No need to apologize for suggesting Jenny's site. She gets a TON of inquiries from diabetics and is probably more familiar with what might be causing this pattern.
CarbSane said…
Hey lucy, this appears to be dealing only with postprandial blood sugar levels.

You appear to have isolated impaired fasting glucose (IFG). Sigh, I hate when drama sidetracks me because I have an interesting paper to get around to blogging on regarding the incidence if IFG and IGT. As Karen states, you'd be diagnosed diabetic with your IFG, but it sounds like your postprandial insulin response is normal. The elevated FBG is usually indicative of hepatic insulin resistance -- failure to suppress gluconeogenesis adequately -- metformin may be in order here. Interestingly, IFG does not appear to be as predictive of problems as IGT, so that may be relatively good news for you. How's your HbA1c? Also here I'd love to know NEFA levels but they aren't routinely measured.

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