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Gladys Chia
Chew Yu Mei
Yvonne Teo
Cornelyus Ng
Lau Leslie

15 August 2008

10:58:00 PM

Topic: Oral Glucose Tolerance Test (OGTT)

Hello mates! I have been rotating around the entire lab every week ever since SIP started. So, for this week I am at the Biochemistry section. But anyway, I think OGTT is under Clinical Chemistry.

This section's samples are mostly done automatedly except for OGTT (urine samples) and G6PD Quantitative Test. I will be sharing information about OGTT from my experience, it involves both blood and urine samples. The principle of OGTT is to measure the blood glucose levels in the body and to diagnose Diabetes. The patient have to start fasting the night before from 10pm onwards till the samples are collected next morning at 8am. 3 sets of blood and urine samples are collected over 3 different timing; Fasting, 1st hour and 2nd hour. 75 grams of Dextrose is taken by the patient after the collection of the Fasting sample, which is to challenge the ability of the pancreas to secrete insulin in response to hyperglycemia and the body's response to insulin action. These will be reflected by the rise and fall of blood and urine glucose concentration. Through this entire test, the patient must avoid any activity that may cause false positive results and only water can be taken.

Blood OGTT:
Blood samples are collected in Heparin tube for the Fasting period, this is so because there maybe an additional test for HbA1c. For the following 2 periods, they are collected in Potassium Oxalate tubes to preserve the decreasing of glucose in the plasma/serum. This test is automated, so the centrifuged sample have to be loaded into Cobas Integra 400plus machine which we use it for most of the biochemistry tests.

Picture taken with permission.
Picture taken with permission.

The reference values are:
Normal glucose tolerance--Less than 6.0mmol/l
Impaired glucose tolerance--6.1mmol/l to 6.9mmol/l
Diabetes Mellitus--More than 7.0mmol/l

Normal results:
Fasting--Less than 7.8mmol/l
1st hour--High levels, not significant
2nd hour--Less than 11.1mmol/l

Blood glucose levels are considered more of an importance diagnosis of diabetes compared to urine glucose. As urine glucose only shows that the body cannot absorb further glucose, thus it gets excreted out. The 1st hour results will show an increase in glucose levels with an intake of Dextrose after the Fasting samples are collected, thus these are considered insignificant. Diabetic patient's results will show values more than 7.8mmol/l and 11.1mmol/l for the Fasting period and 2nd hour.

Urine OGTT:
Urine samples are collected in clean containers and tested for the presence of glucose and ketones using Keto Diabur-Test 5000 dipsticks. Glucose in urine are the indication of diabetes as normal results will not show a positive test. Ketones(acetone) in the urine is a result of an increased breakdown of body fat during weight reduction dieting or poor glucose utilization due to insulin deficiency. If there is a positive result of ketones, it may indicate that the patient is suffering from insulin deficiency and imminent diabetic ketoacidosis.

Method:
1. Immerse dipstick in urine for less than 1 second.
2. Remove excess urine by wiping the edge of the dipstick against the rim of the urine container.
3. Wait for 1 minute and read the Ketone test area.
4. Wait for another 1 minute and read the Glucose test area.

Normal results for ketone test area:
Fasting--Negative
1st hour--Negative
2nd hour--Negative

Normal results for glucose test area:
Fasting--Negative
1st hour--Trace results or 1+ (its insignificant due to intake of dextrose)
2nd hour--Negative or Trace results

Diabetic patient's results will reflect a 1+/2+/3+ on the glucose test area for the 1st and 2nd hour, and ketone test area are usually negative. When the urine results are out, the blood glucose results are checked and re-run again to ensure that the patient is diabetic.

Okay, thats all. Hopefully my information is clear enough for you people to understand (:

Yvonne Teo, TG01

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