Interpretive Handbook

The most common disease related to carbohydrate metabolism is diabetes mellitus. Insufficient blood levels of active insulin characterize diabetes mellitus. Symptoms include polyuria, abnormally elevated blood and urine glucose values, excessive thirst, constant hunger, sudden weight loss and possibly elevated blood and urine ketones. Complications from diabetes are the third leading cause of death in the US. There are approximately 16 million diabetics in the US and that number is growing. It is estimated that at least 5 million of these people have not been diagnosed. The prevalence in the population age 65 and older is 18.4%, representing 6.3 million cases. The cost of diabetes to the US economy exceeds $92 billion annually.

Over production or excess administration of insulin causes a decrease in blood glucose to levels below normal. In severe cases the resulting extreme hypoglycemia is followed by muscular spasm and loss of consciousness, known as insulin shock.

Glucose levels are used to diagnose and manage diabetes mellitus and other carbohydrate metabolism disorders including gestational diabetes, neonatal hypoglycemia, idiopathic hypoglycemia, and pancreatic islet cell carcinoma.

Any of the following results, confirmed on a subsequent day, can be considered diagnostic for diabetes:  

-fasting plasma or serum glucose > or = 126 mg/dL after an 8-hour fast

-2-hour plasma or serum glucose > or = 200 mg/ dL during a 75-gram oral glucose tolerance test (OGTT)

-random plasma or serum glucose >200 mg/ dL plus typical symptoms.

Patients with "impaired" patients are those whose fasting serum or plasma glucose falls between 110-126 mg/dL or whose 2-hour value on OGTT fall between 140-199 mg/dL. These patients have a markedly increased risk of developing type 2 diabetes and should be counseled for lifestyle changes and followed up with more testing. Indications for screening/testing include strong family history, marked obesity; history with babies over 9 pounds, and recurrent skin and genitourinary infections.

Glucose levels < or = 25 mg/dL in infants <1 week are considered to be potentially life threatening as are glucose levels < or = 40 mg/dL in infants >1 week.

Once the blood is drawn, the cells in the blood will begin to metabolize the glucose that is present. At room temperature, glucose in the blood will decrease by 10% per hour. Therefore, in a non-gel separator tube, the specimen should be centrifuged as soon as possible and the plasma or serum removed from the cells. If the blood is drawn in a serum or plasma separator tube, the glucose is stable once the sample has been spun and the gel is in place. Inhibitors of glucose metabolism such as fluoride can be used. Glycolysis will take place but at a much reduced rate, approximately 10% over 3 hours.

0-11 months: not established

> or =1 year: 70-100 mg/dL

Tietz Textbook of Clinical Chemistry. 4th edition. Edited by CA Burtis, ER Ashwood, DE Bruns. WB Saunders Company, Philadelphia, 2006; 5:837-901