(Oral Glucose Tolerance Test with Concurrent Insulin Levels)

Click here to return to IR Index

The following
1. Gives examples of Case histories along with GTT insulin test results.
2. Describes how improper insulin testing can distort the results.
3. Describes precautions your lab needs to follow to get good insulin test results.
4. Gives examples of normal and abnormal GTT insulin test results.

Case 1 - A woman aged 53, about whom the local family doctor wrote in the letter of referral re: Blood Glucose Nice lady.... Multiple problems & long term problem. I feel there might be a sugar problem. Regards, J."

She had in fact been "Unwell for 10 years; started with migraine; started to get scatter-brained & couldn't concentrate". The rest of her history & examination was unremarkable. The doctor enclosed a copy of a GTT/INS performed by a laboratory I suspected did not transport (400km) on dry-ice to the main lab. where the insulin assay would be done. The results being:-

29/01/96---------Fasting ----1hour after glucose ----2hours after
Blood glucose-----5.5 -----------8.1-------------------7.1
Blood insulin------11------------26--------------------20
Normal insulin*-- 2-10---------9-45-----------------5-30

(*"Normal " insulin levels vary between authorities; the above are the values which I still use. AG March 27 2002)

I phoned the lab which had done the test & was told :-" No,
although the serum had been separated, their lab did not consider
it necessary to freeze specimens for transport".. to the main Lab
400 km away.

I repeated the same test at the IMVS, in Whyalla, where I know the protocol follows** my requirements & the following results

Blood glucose-------6.1---------9.0-----------6.2
Blood insulin-------12---------155-----------117
normal insulin*-<14-------<80----------<60
* see comment above

(** Transport on dry ice abandoned from all country centres except Gribbles at Whyalla where insulin assays are performed on site; also some laboratories no longer measure values at one hour when in my experience, insulin levels peak! AG March 27 2002)
Quite clearly the first test had given false values. It would appear that the transport of the specimen adversely affected the insulin level; I wonder whether the constant shaking of the specimen during transport promoted adhesion to the plastic tube carrying the serum.

SO THE MESSAGE IS -- If you want to have an insulin assay, let them treat your specimen with the utmost respect and transport it on dry ice (frozen carbon dioxide); that way it cannot slop around- nor is water ice satisfactory in my opinion because serum remains liquid at 0 degrees C-they use dry ice to transport icecream out here in Australia. The problem is:- the labs. are under pressure to contain costs; but if we look at the big picture we find incredible costs incurred with other more acceptable tests;let me give you another case history:-

Case 2 "A 15 year old lass was referred to me on 14/11/95 with a letter from her doctor which reads:-"Thanks for your help with this girl who is something of a mystery to us. She presented in August with a 4 week history of fatigue, headaches and malaise, together with quite marked hip & shoulder girdle pain. At one stage it had been suggested that it was stress but, although she is in fairly intensive studies, I did not think this was likely. Blood tests showed thalassaemia minor-unrelated to her acute symptoms, I'm sure. She was seen by R..P..(a Physician specialist) who noted negative Thyroid Function, Paul Bunnell, WCC, differential, borderline rheumatoid ( later checked-normal), antinuclear antibody, IgGAM, protein electrophoresis, and CRP. Her CK was normal. Interestingly her total IgE was elevated at 605 (R<151) She is currently taking Claratyne (an antihistamine) and rhinocort on an impirical basis. She reports some improvement in her limb aches but the headache is still severe. Following up the IgE, her RAST showed some high reactivities and I enclose a copy. I appreciate your assistance, etc." The RASTS showed multiple strong positives to pollen, animal housedust-mite and mould mixes.

History revealed a diet low in protein and high in carbohydrates including sugar, chocolate & "lots of fruit"-usually 4 or 5 pieces a day; she loved pasta & noodles.

Her GTT/INS showed normal glucose but marked hyperinsulinaemia; this
constitutes insulin resistance. the results are below:-

Test at Clinpath December 1995

------------Fasting--1hour after glucose--2hours after glucose
Blood glucose---5.3----------7.3---------------5.6
Blood insulin----21-------->300-----------186

Normal insulin*--2-10-------9-45-------------5-30

Correction of the diet in this lass has seen a remission of symptoms except when she had some prepacked coffee milk (ironically) labelled "Take Care" The reaction was transient & additives were blamed but I wonder if it was the extra intake of milk & it's content of milk sugar not balanced by a portion of complex carbohydrate and adequate protein; I have more questions than answers as far as diet is concerned.

Allen E. Gale 27 9 96

Click here to return to IR Index