Oral Glucose Tolerance Test (OGTT)- Urine sample

How is the test Result Interpreted?

Result interpretation is as per American diabetes association guidelines 2017.

For Fasting(8 hours), <100 is Normal,  Impaired fasting glucose is 100-125 & Diabetes mellitus is  >/=126

And that for 2 hours OGTT,  <140 is Normal,  Impaired fasting glucose is <140, Impaired glucose tolerance is 150-199 & Diabetes mellitus is >/=200

What is Diabetes Mellitus?

Diabetes Mellitus (DM) is a metabolic disorder in which there is either deficiency or there is reduced effectiveness of insulin resulting in a condition of persistent hyperglycemia.

Various important metabolisms which require insulin-like carbohydrate, protein and fat, get deranged.

The characteristic features of DM include:

a)    Fasting hyperglycemia
b)   Symptoms of persistent marked hyperglycemia: polyuria, polydipsia, polyphagia. Also blurring of vision is noted.
c)    Glycosuria
d)   Long term complications: 

• Macroangiopathy : Atherosclerosis( which can further progress to ischemic heart disease, cerebrovascular attacks and peripheral vascular diseases).
• Microangiopathy: nephropathy- may lead to renal failure.
• Retinopathy-may progress to loss of vision
• Peripheral neuropathy: may lead to foot ulcers which may progress upwards and require amputation.

e)    Acute metabolic complications: hyperosmolar hyperglycemic state or diabetic ketoacidosis.
f)      Increased susceptibility to infections: skin, respiratory tract, and urinary tract.

What is the action of insulin in the human body?

Insulin is the most important hormone maintaining glucose metabolism in the body. It is produced in the β cells of pancreas as preproinsulin. This preproinsulin is further broken down to insulin and C-peptide. In conditions of high glucose levels in the body, both insulin and C-peptide are released in the blood circulation.

Major actions of insulin are:

• It increases the uptake of glucose in skeletal muscle and adipose tissue.
• Stimulates process of glycogen formation in liver and muscle (glycogen is the storage form of glucose. In conditions of low glucose, this glycogen is broken down to release glucose)
• Synthesis of fatty acids in the liver and adipose tissue
• Protein synthesis in liver and muscle.

It decreases: 

• Gluconeogenesis in the liver (glucose formation is reduced).
• Glycogenolysis in liver and muscle (inhibits the breakdown of glycogen).
• Breakdown of fat in adipose tissue
• Production of ketones in the liver.

What is the role of C-peptide?

C-peptide is used only as a marker of the activity of β cells. It has no known function.

What is the American Diabetes Association (ADA) Classification?

As per ADA classification:

There are two major types of DM

a) Type 1(absolute deficiency of insulin) occurs due to the destruction of β cells of the pancreas.
b) Type 2 ( insulin resistance along with relative deficiency of insulin secretion)

What is gestational diabetes?

GDM is the condition in which there is onset or first recognition of glucose intolerance during the period of pregnancy. This condition is seen in two to three percent of pregnant women.

Complications related to GDM include:

• High birth weight of new-born
• Cardiac defects
• Polyhydramnios
• Intrauterine fetal death (IUFD)
• Premature birth
• Eclampsia or preeclampsia

What are the various blood investigations done to diagnose Diabetes Mellitus (DM)?

The two major tests done: 

a) Estimation of blood glucose 

Estimation can be done from three different samples:

• Fasting plasma glucose-blood collected after overnight fasting of at least eight hours.
• Post-meal or postprandial (PP) glucose-blood withdrawn after two hours of food intake (normal regular meal) by the patient
• Random blood glucose-blood collected at any time of the day, irrespective of the time of last food intake.

b) Oral glucose tolerance test (OGTT)

What is GlycoHB?

Glycated hemoglobin is the percentage of hemoglobin that is attached with glucose molecules irreversibly and non-enzymatically. Its amount depends upon plasma glucose level and lifespan of RBC's. Plasma glucose readily moves across the red cell membrane and gets attached to hemoglobin. Once attached this cannot be reversed for the lifespan of RBC. This test gives an estimate of plasma glucose for the last 8-12 weeks. As the blood glucose level increases, the percentage of glycated hemoglobin also increases. Normally less than 5% of hemoglobin is glycated.HBA1C value of 6% indicates approximate average plasma glucose of 135mg/dl which increases by 35 mg with a 1% rise in glycoHB. In a diabetic person, it is recommended to monitor glucose control by this test as it gives an estimate of control over sugar for the last 2-3 months as against random or fasting, postprandial glucose which tells estimate of short term control.