Blood Glucose test is a direct measurement of the blood glucose level. It is most commonly used in the evaluation of diabetic patients. Through an elaborate feedback mechanism, glucose levels are controlled by insulin and glucagon. Glucose levels are low in the fasting state. In response, glucagon, which is made in the alpha cells of the pancreatic islets of Langerhans, is secreted. Glucagon breaks glycogen down to glucose in the liver and glucose levels rise. If the fasting persists, protein and fatty acids are broken down under glucagon stimulation. Glucose levels continue to rise.
Glucose levels are elevated after eating. Insulin, which is made in the beta cells of the pancreatic islets of Langerhans, is secreted. Insulin attaches to insulin receptors in muscle, liver, and fatty cells, in which it drives glucose into these target cells to be metabolized to glycogen, amino acids, and fatty acids. Blood glucose levels diminish. Many other hormones (e.g., adrenocorticosteroids, adrenocorticotropic hormone [ACTH], epinephrine, growth, thyroxine) can also affect glucose metabolism.
The serum glucose test is helpful in diagnosing many metabolic diseases. Serum glucose levels must be evaluated according to the time of day they are performed. For example, a glucose level of 135 mg/dL may be abnormal if the patient is in the fasting state, but this level would be within normal limits if the patient had eaten a meal within the last hour.
In general, true glucose elevations indicate diabetes mellitus (DM), however, there are many other possible causes of hyperglycemia. Similarly, hypoglycemia has many causes. The most common cause is inadvertent insulin overdose in patients with brittle diabetes. If diabetes is suspected based on elevated fasting blood levels, a glycosylated hemoglobin or glucose tolerance test can be performed.
Glucose determinations must be performed frequently in new diabetic patients to monitor closely the insulin dosage to be administered. Finger stick blood glucose determinations are often performed in the morning, before meals, or at bedtime. Results are compared with a sliding-scale insulin chart ordered by the physician to provide coverage with subcutaneous regular insulin.
Normal Blood Glucose Levels
Normal Blood Glucose Levels vary by age. Blood sugar levels are normally low at younger age and the Normal Levels of Blood Glucose increases as the person grows. It it normal for healthy elderly people to have higher blood sugar than healthy adults.
Blood glucose is measured either in terms of Milligrams per Deciliter (mg/dL) or in terms or Millimole per Liter (mmol/L) in labs that use SI units . The following listing shows the Normal Glucose Levels at different age groups:
Premature Infant: 20 to 60 mg/dL (1.1-3.3 mmol/L)
Neonate: 30 to 60 mg/dL (1.7-3.3 mmol/L)
Infant: 40 to 90 mg/dL (2.2-5.0 mmol/L)
Child younger than two years of age: 60 to 100 mg/dL (3.3-5.5 mmol/L)
8 hours Fasting Adult or Child above two years of age: 70 to 110 mg/dL ( Less than 6.1 mmol/L)
Non-fasting Adult or Child above two years of age: Above 200 mg/dL ( Above 11.1 mmol/L)
When pregnant, several women may experience a condition known as Gestational Diabetes. Gestational Diabetes occurs as a result of the physiological changes women experience during pregnancy. Some of these changes may affect the hormones that tolerate the blood sugar levels in the body.
Causes of High Blood Glucose Levels
Diabetes mellitus (DM): This disease is defined by glucose intolerance and hyperglycemia. A discussion of the many possible etiologies is beyond the scope of this manual.
Acute stress response: Severe stress, including infection, burns, and surgery, stimulates catecholamine release. This in turn stimulates glucagon secretion, which causes hyperglycemia.
Cushing syndrome: Blood cortisol levels are high. This in turn causes hyperglycemia.
Pheochromocytoma: Catecholamine stimulates glucagon secretion, which causes hyperglycemia.
Chronic renal failure: Glucagon is metabolized by the kidney. With loss of that function, glucagon and glucose levels rise.
Glucagonoma: Glucagon is autonomously secreted, causing hyperglycemia.
Acute pancreatitis: The contents of the pancreatic cells (including glucagon) are spilled into the bloodstream as the cells are injured during the inflammation. The glucagon causes hyperglycemia.
Diuretic therapy: Certain diuretics cause hyperglycemia.
Corticosteroid therapy: Cortisol causes hyperglycemia.
Acromegaly: Growth hormone stimulates glucagon, which causes hyperglycemia.
Acute Salicylate Toxicity.
Drugs that cause High Blood Glucose Levels include:
- Tricyclics Antidepressants.
- Beta-adrenergic Blocking Agents.
- IV Dextrose Infusion.
Causes of Low Blood Glucose Levels
Insulinoma: Insulin is autonomously produced without regard to biofeedback mechanisms.
Hypothyroidism: Thyroid hormones affect glucose metabolism. With diminished levels of this hormone, glucose levels fall.
Hypopituitarism: Many pituitary hormones (adrenocorticotropic hormone [ACTH], growth hormone) affect glucose metabolism. With diminished levels of these hormones, glucose levels fall.
Addison disease: Cortisol affects glucose metabolism. With diminished levels of this hormone, glucose levels fall.
Extensive liver disease: Most glucose metabolism occurs in the liver. With decreased liver function, glucose levels decrease.
Insulin overdose: This is the most common cause of hypoglycemia. Insulin is administered at too high of a dose (especially in brittle diabetes) and glucose levels fall.
Starvation: With decreased carbohydrate ingestion, glucose levels diminish.
Drugs that cause Low Blood Glucose Levels include:
- Alpha-glucosidase Inhibitors.
- Anabolic Steroids.
- Incretin Mimetics.
- Monoamine Oxidase Inhibitors.