Estimation of Blood Glucose & Blood Sugar.

Estimation of Blood Glucose

Estimation of Blood Glucose &  Blood Sugar

• Specimens needed for Blood Glucose Estimation
• Collection of specimen

1. Fasting specimen 
2. Post-prandial specimen
3. Random specimen 

Estimation of sugar/glucose levels in the blood methods

Definition of Blood Glucose &  Blood Sugar

Glucose is the main carbohydrate in the blood, but the term blood sugar" is generally used to include glucose, other sugars and reducing substances that may be present in the blood.

• Some methods of estimation of glucose depend on the reducing properties of the sugar. These properties are shared by other sugars and reducing substances.

• Thus, these methods are not specific for glucose; and such estimations are expressed as Blood Sugar estimations.

• When the non-glucose reducing substances are removed as part of glucose determination, the resulting value is known as the true glucose value.

• Other methods like the oxidase-peroxidase method, confer a high degree of specificity on the measurement of glucose in blood and urine.

Specimens needed for Blood Glucose Estimation

Blood glucose is usually measured on a protein-free filtrate of whole blood. This normally gives a value lower than that of plasma due makes use of plasma instead of serum or whole blood. Glucose estimation using plasma or whole blood requires the use of an anticoagulant. 

• The fluoride-oxalate mixture used for this purpose is composed of 2 mg of sodium fluoride and 6 mg of potassium oxalate per ml of blood. More than 5 mg of sodium fluoride per ml of blood acts as an inhibitor for the enzymatic estimations.

Collection of specimen

for measurements of blood glucose level should be done on the day and time requested. This is because collection times are usually related to food intake, insulin treatment, or both. 

• It may be necessary sometimes to note the time of blood collection on the specimen container and on the patient's request form. 

• Urgent glucose measurement becomes necessary in cases of severe hypoglycemia or hyperglycaemia as both conditions can result in loss of consciousness (coma).

Fasting specimen refers to blood collected after a period of no food intake. For adults, fasting time is usually 10 to 16 hours, while for children, it is 6 hours. 

Post-prandial specimen is blood collected usually 2 hours after a meal has been eaten. 

Random specimen refers to blood sample collected at any time regardless of food consumption. Collection of blood samples for glucose tolerance test is described separately. 

Four methods are described in this blog for the estimation of sugar/glucose levels in the blood. 

They are:

1. Oxidase-peroxidase method:

2. Reduction of cupric to cuprous salt (Folin-Wu method):

3. Reflometric method

4. O-Toluidine method

 

False glucose levels A false high glucose level may result if blood sample is collected from an arm receiving an intravenous (i.v.) infusion. Icteric samples can likewise give falsely low glucose levels.

Causes of Abnormal Glucose Levels
Severe hyperglycaemia	Mild/transient hyperglycaemia	Severe hypoglycaemia
1. Diabetes mellitus	1. Severe liver disease	1. Insulinoma
2. Adrenal cortical hyperactivity (Cushing's syndrome)	2. Pancreas disorder	2. Hypopituitarism
3. Acromegaly	3. Pituitary disorder	3. Ectopic insulin production from tumours
4. Obesity	4. Steroid therapy	4. Adrenal cortical insufficiency
	5. Shock 6. Convulsions
	7. Acute stress reaction (Physical or emotional)