Clinical and Interpretive

Measurement of glucose is useful in diagnosing and managing diabetes mellitus and other carbohydrate metabolism disorders including gestational diabetes, neonatal hypoglycemia, idiopathic hypoglycemia, and pancreatic islet cell carcinoma.

The most common disease related to carbohydrate metabolism is diabetes mellitus which is characterized by insufficient blood levels of active insulin. 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 United States. There are approximately 16 million diabetics in the United States, 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.

Overproduction 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.

Any of the following results, confirmed on a subsequent day, can be considered diagnostic for diabetes:
-Fasting plasma or serum glucose ≥126 mg/dL after an 8-hour fast
-2-Hour plasma or serum glucose ≥200 mg/ dL during a 75-gram oral glucose tolerance test (OGTT)
-Random glucose >200 mg/dL, plus typical symptoms

Patients with “impaired” glucose regulation are those whose fasting serum or plasma glucose fall between 101 and 126 mg/dL, or whose 2-hour value on oral glucose tolerance test fall between 140 and 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 and testing include strong family history, marked obesity, history of babies over 9 pounds, and recurrent skin and genitourinary infections.

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

Once the blood is drawn, the cells in the blood begin to metabolize the glucose that is present in the specimen. At ambient temperature, the glucose concentration 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 SST or PST, the glucose is stable once the specimen has been spun and the gel is in place. Inhibitors of glucose metabolism such as fluoride also can be used. In these tubes, glycolysis will take place, but at a much reduced rate (approximately 10% over 3 hours).