Glucose

Glucose is the primary energy source for the human body.

Sources of glucose in the blood: Dietary carbohydrates: After digestion and breakdown

of dietary carbohydrates and absorption of glucose , a state of postabsorptive hyperglycaemia is realized.

Glycogenolysis: Free blood glucose can be derived from the liver stores of glycogen.

Gluconeogensis: Blood glucose is derived through its endogenous synthesis from non-carbohydrate sources e.g. from amino acids, lactate and glycerol.

Serum GLUCOSE level

Normal Value (fasting) = 60 – 110 mg/dl

HYPERGLYCEMIA

• Causes of increased serum glucose level• 1- DIABETIS MELLITUS• 2- Diabetic ketoacidosis• 3- Hyperthyroidism• 4- Hyperpitutirism

HYPOGLYCEMIA

• Causes of decreased serum glucose• 1- hyperinsulinism• 2- hypopitutrism

The glucose level in blood is maintained within a fairly narrow range under diverse conditions (feeding, prolonged fasting or severe exercise) by regulatory hormones such as: insulin, glucagon or epinephrine.

Estimation of serum glucose level by colorimeter

Enzymatic Colorimetric method

Principle: Glucose Oxidase Glucose H2O2 + Gluconic acid

2H2O2 + phenol + 4-amino – antipyrine Peroxidase

Colored quinone + 4H2O

Sample:Serum or plasma.

Working Reagent: Glucose oxidase Peroxidase Phenol 4-amino-antipyrine Phosphate buffer

Procedure:

Blank (ml)

Standard (ml)

Sample (ml)

Sample or

Standard - 0.01 0.01

Working

Reagent 1 1 1

Mix Well. Incubate for 10 minutes at 37°C. Measure the absorbance of sample

(A sample) and the standard (A standard).

Calculation:

Glucose concentration in the sample (mg/dl) =

A sample x Conc. Standard(100)

A standard

Glucose Tolerance

The ability of the body to utilize glucose is ascertained by measuring its glucose tolerance.

To determine the glucose tolerance curve, the patient comes fasting and a blood sample is withdrawn for determination of fasting serum glucose level.

Patient is asked to take 75 g of glucose orally. A blood sample is withdrawn every 30 minutes for 2-3

hours. Serum glucose level is determined in each sample and the results are plotted against time.

The resultant curve is known as glucose tolerance curve which has the following features in normal individuals:

Fasting level:

Usually between 60-110 mg/dl. After taking the oral glucose dose, absorption occurs

rapidly and the blood glucose concentration increases. After 30-60 minutes:

Serum glucose level reaches its maximal value but still below the renal sugar threshold RST (180mg/dl) e.g. it reaches a level of 140-150 mg/dl.

This stimulates the secretion of insulin for better utilization of the absorbed glucose

120 minutes: Serum glucose level drops to a level below the fasting

level due to excess production of insulin. This temporally existing hypoglycaemia is beneficial in

switching off the secretion of insulin after which the fasting level is regained and then maintained

More than 120 minutes: Fasting level is reached and is then maintained.

After 30-60 minutes: (at the maximal value of the curve),

the rate of absorption of glucose is equal to its rate of utilization.

Before this value (at the ascending limb of the curve) the rate of absorption is greater than the rate of utilization

While after this value (at the descending limb of the curve) the rate of utilization is greater than the rate of absorption

Characteristics of the diabetic curve:a) Mild diabetes mellitus: The fasting glucose level is higher than normal (but still

below the RST). After oral glucose administration the blood glucose level

rises and exceeds the renal sugar threshold (glycosuria is accompanied).

The decline in the curve is slower than normal and by its end, it is maintained at a level higher than the fasting level but lower than RST (no glycosuria).

b) Severe diabetes mellitus:The fasting glucose level is higher than normal and may exceed the RST (glycosuria).

After oral glucose administration the blood glucose level rises to a very high levels.

The decline in the curve is slower than normal and its end is maintained at a high level which is above the RST and is much higher than the fasting level.

Glycosuria is present during and after the test

0

50

100

150

200

250

300

350

fasting 30 60 90 120

HyperinsulinlismNourmal

MildModerate

ModerateRST 180 mg/dl

Renal Sugar Threshold (RST) 180

mg/dL

Time in minutes

Serum glucose (mg/dL)

Significance of glucose tolerance curve:

(1) It helps in diagnosis of pre-diabetics (people who are liable to develop diabetes mellitus). These people show normal fasting levels of blood glucose, however their glucose tolerance curves show a sort of diabetic curves.

(2) Adjustment of the dose of hypoglycaemic drugs in diabetic patients.

A fasting sample is first taken, then the patients takes his usual dose of the hypoglycaemic drug, followed by an oral dose of 75 g glucose, and then the test is performed.

If the hypoglycaemic dose is satisfactory, the patients will have a curve which is similar to the normal curve.

If the hypoglycaemic dose in inadequate, the patient will still have a sort of a diabetic curve.

Excess dose may lead to a hyperinsulinism curve.

Fructosuria Definition Presence of fructose in urine

Causes:1-Essential fructosuria: Due to hereditary deficiency of fructokinase enzyme

2-Hereditary fructose intolerance: Due to hereditary deficiency of aldolase B enzyme. F-1-P will be accumulated leading to inhibition of

glycogen phosphorylase, thus preventing breakdown of glycogen>>> hypoglycemia after fructose feeding.

How to detect fructose in urine:

Seliwanoff’s test:

2 mL of Seliwanoff’s reagent+ 1 mL of urine and boiling.

Red onion peal color will appear if urine contains fructose.