Partial preview of the text
Download GLUOSE TOLERANT TEST and more Slides Earth science in PDF only on Docsity!
REGULATION OF BLOOD GLUCOSE * Efficiently regulated system. * Continuous supply of glucose to the brain, RBC and renal medulla is needed. Fig. 24.3. Overview of regulation of blood glucose Regulation in Fasting State * i. Normally, 2 to 2% hours after a meal, the blood glucose level falls. * ii. For another 3 hours, hepatic glycogenolysis, gluconeogenesis, Hormones like glucagon, epinephrine, glucocorticoids, growth hormone, ACTH and thyroxine will take care of the blood glucose level. as +e : a ” aes na aL Par 2A, Blood gluccse regulction during tastng face again cane state (high glucagon. In fasting siate, blood glucose —_prandial state (high insulin) In post-prardisl state Fig. 24.3. Overview of regulation of blood gluccse Determination of Glucose in Body Fluids ¢ Estimation of glucose is the most common analysis done in clinical laboratories. * The blood is collected using an anticoagulant (potassium oxalate) and an inhibitor of glycolysis (sodium fluoride). * Plasma is separated for glucose estimation. ¢ Enzymatic Method * This is highly specific, giving ‘true glucose’ values (fasting 70-110 mg/dl ). * The glucose oxidase (GOD) method is the one most widely used. * Glucose oxidase is very specific; it converts glucose to gluconic acid and hydrogen peroxide. Commonly Employed Terms Regarding Glucose * 1. Random plasma glucose. (70-140 mg/dl) ° 2. Fasting plasma glucose, an overnight fast (12 hours after the food) . ° 3. 2 hr after a good meal is called post-prandial plasma glucose (Latin = after food). ¢ 4. Normoglycemia, hyperglycemia, hypoglycemia. (Greek, hyper = above; hypo = below). ¢ 5. When the plasma glucose is below 50 mg/dl, it is a very serious condition. Hyperglycemia is harmful in the long run; while hypoglycemia even for a short while is dangerous, and may even be fatal. WHAT IS GLUCOSE TOLERANCE TEST * The ability of a person to metabolise a given load of glucose is referred to as glucose tolerance. ¢ TWO WAYS TEST ¢ 1. ORAL GTT- Classic and Modern or mini OGTT ¢ 2. INTRAVENOUS GTT Conducting the Glucose Tolerance Test ° 1. At about 8 am, a sample of blood is collected in the fasting state. Urine sample is also obtained. This is denoted as the "0" hour sample. ¢ 2. Glucose Load Dose: The dose is 75 g anhydrous glucose (82.5 g of glucose monohydrate) in 250- 300 ml of water. This dose is fixed for an adult, irrespective of body weight. (When the test is done in children, the glucose dose is adjusted as 1.75 g /kg body weight). ¢ 3. Sample Collection: As per current WHO recommendations, 2 samples are collected, one at fasting ("0" hr sample) and 2 hr post-glucose load. Urine samples may also be collected along with these blood samples. Normal Values and Interpretations ¢ As per WHO recommendation, In a normal person, fasting plasma glucose is 70-110 mg/dl. ¢ The present day tendency is to view values above 100 at oe Diabetes mallilus mg/ml as suspicious. * According to the recommendations of the American Diabetic Association, the revised upper limit is 100 mg/dl, above which a person has to be further tested periodically. id S IT Renal threshold * Currently the International Diabetes Federation says that a value more than 100 mg/dl is one of the criteria for the metabolic syndrome. Impaired GT s ¢ Following the glucose load, the level rises and reaches a peak within 1 hour and then comes down to normal fasting levels by 2 to 2% hours. Plasma glucose mg/dl S l Normal on a I ¢ This is due to the secretion of insulin in response to the elevation in blood glucose. * None of the urine sample shows any evidence of T T T T T glucose. 0 1 2 Hours Indications for OGTT * 1. Patient has symptoms suggestive of diabetes mellitus; but fasting blood sugar value is inconclusive (between 100 and 126 mg/dl). ¢ 2. During pregnancy, excessive weight gaining is noticed, with a past history of big baby (more than 4 kg) or a past history of miscarriage. ¢ 3. To rule out benign renal glucosuria. Contraindications for OGTT * 1. There is no indication for doing OGTT in a person with confirmed diabetes mellitus. ¢ 2. GTT has no role in follow-up of diabetes. It is indicated only for the initial diagnosis. ¢ 3. The test should not be done in acutely ill patients. Difference between modern and classical GTT * Glucose load given is the same in both instances. * In the classical procedure, the blood and urine samples are collected at % an hour intervals for the next 2% hours. (Total six samples, including 0 hr sample). * Glucose is estimated in all the blood samples. * Urine samples are tested for glucose qualitatively. * In modern times, only 2 blood samples are collected. ° Figure 24.4 represents the graph, when plasma glucose values are plotted on the vertical axis against the time of collection on the horizontal axis. lates erties Causes for Abnormal GTT Curve * 1. Impaired Glucose Tolerance (IGT) * It is otherwise called as Impaired Glucose Regulation (IGR). * Here plasma glucose values are above the normal level, but below the diabetic levels (see Table 24.1). ° In IGT, the fasting plasma glucose level is between 110 and 126 mg/dl and 2- hour post glucose value is between 140 and 200 mg/dl (Fig. 24.4). * Such persons need careful follow-up because IGT progresses to frank diabetes at the rate of 2% patients per year. ¢ 2. Impaired Fasting Glycemia (IFG) * In this condition, fasting plasma glucose is above normal (between 110 and 126 mg/dl); but the 2 hour post-glucose value is within normal limits (less than 140 mg/dl). ¢ These persons need no immediate treatment; but are to be kept under constant check up. REDUCING SUBSTANCES IN URINE ¢ Normally glucose is not excreted in urine. * But if blood glucose is more than 180 mg/dl, urine contains glucose. * The blood level of glucose above which glucose is excreted is called renal threshold. * The excretion of reducing substances in urine is detected by a positive Benedict's test (see Chapter 6). * About 0.5 ml of urine is boiled with 5 ml Benedict's reagent for 2 minutes (or kept for 2 minutes in water bath which is already boiling). ¢ The formation of a precipitate is observed on cooling. ¢ The test is semi-quantitative and the color of the precipitate roughly parallels the concentration of reducing sugar. * Blue color indicates the absence of sugar in urine. * The green precipitate means 0.5%; yellow (1%); orange (1.5%) and red indicates 2% or more of sugar (1% means 1 g per 100 ml). * Nowadays, strips are available, which when dipped in urine will give the color, if it contains sugar. 
