Glucose, Whole Blood, Serum, Plasma

Definition

A blood glucose test measures the amount of a type of sugar, called glucose. Glucose comes from carbohydrate foods and is the main source of energy used by the body. Glucose levels are regulated by insulin and glucagon.
Normal ranges: see Table 16.38.

TABLE 16 " 38Normal Ranges for GlucoseView LargeTABLE 16 " 38Normal Ranges for Glucose Age Reference Range Critical Range 0 " 4 mo 50 " 80 mg/dL <35, >325 mg/dL 4 mo " 1 y 50 " 80 mg/dL <35, >325 mg/dL >1 y 70 " 99 mg/dL <45, >500 mg/dL

Use

Diagnosis of DM
Control of DM
Diagnosis of hypoglycemia
Other carbohydrate metabolism disorders including gestational diabetes, neonatal hypoglycemia, idiopathic hypoglycemia, and pancreatic islet cell carcinoma
Criteria for the diagnosis of DM (American Diabetes Association Expert Committee)
- Four ways to diagnose diabetes are possible. Each must be confirmed on a subsequent day by any one of the four methods given above.
  - Symptoms of diabetes plus casual (random) plasma/serum glucose concentration ≥200 mg/dL (11.1 mmol/L). Casual is defined as any time of day without regard to time since the last meal.
  - FPG (fasting plasma glucose) ≥126 mg/dL (7.0 mmol/L). Fasting is defined as no caloric intake for at least 8 hours.
  - Two-hour PG (postload glucose) ≥200 mg/dL (11.1 mmol/L) during an OGTT. The test should be performed using a 75-g glucose load.
  - HbA1C of >6.5%.
- In the absence of unequivocal hyperglycemia with acute metabolic decompensation, these criteria should be confirmed by repeat testing on a separate day. The third measure (OGTT) is not recommended for routine clinical use.
- The Expert Committee recognizes an intermediate group of subjects whose glucose levels, although not meeting the criteria for diabetes, are nevertheless too high to be considered altogether normal. This group is defined as having FPG levels >110 mg/dL but <126 mg/dL or 2-hour values in OGTT of >140 mg/dL but <200 mg/dL.

Interpretation

Increased In

DM, including:
- Hemochromatosis
- Cushing syndrome (with insulin-resistant diabetes)
- Acromegaly and gigantism (with insulin-resistant diabetes in early stages, hypopituitarism later)
Increased circulating epinephrine
- Adrenalin injection
- Pheochromocytoma
- Stress (e.g., emotion, burns, shock, anesthesia)
Acute pancreatitis
Chronic pancreatitis (some patients)
Wernicke encephalopathy (vitamin B1 deficiency)
Some CNS lesions (subarachnoid hemorrhage, convulsive states)
Effect of drugs (e.g., corticosteroids, estrogens, alcohol, phenytoin, thiazides, propranolol, chronic hypervitaminosis A)

Decreased In

Pancreatic disorders
- Islet cell tumor, hyperplasia
- Pancreatitis
- Glucagon deficiency
Extrapancreatic tumors
- Carcinoma of the adrenal gland
- Carcinoma of the stomach
- Fibrosarcoma
- Other
Hepatic disease
- Diffuse severe disease (e.g., poisoning, hepatitis, cirrhosis, primary or metastatic tumor)
Endocrine disorders
- Hypopituitarism*
- Addison disease
- Hypothyroidism
- Adrenal medulla unresponsiveness
- Early DM
Functional disturbances
- Postgastrectomy
- Gastroenterostomy
- Autonomic nervous system disorders
Pediatric anomalies
- Prematurity*
- Infant of diabetic mother
- Ketotic hypoglycemia
- Zetterstr Άm syndrome
- Idiopathic leucine sensitivity
- Spontaneous hypoglycemia in infants
Enzyme diseases
- von Gierke disease*
- Galactosemia*
- Fructose intolerance*
- Amino acid and organic acid defects*
Methylmalonic acidemia*
Glutaric acidemia, type II*
Maple syrup urine disease*
3-Hydroxy, 3-methyl glutaric acidemia*
- Fatty acid metabolism defects*
Acyl CoA dehydrogenase defects*
Carnitine deficiencies*
Other
- Exogenous insulin (factitious)
- Oral hypoglycemic medications (factitious)
- Leucine sensitivity
- Malnutrition
- Hypothalamic lesions
- Alcoholism

*May cause neonatal hypoglycemia.

Limitations

Most glucose strips and meters quantify whole blood glucose, whereas most laboratories use plasma or serum, which reads 10 " 15% higher.
In whole blood glucose determinations, hematocrit of >55% causes decreased result. Hematocrit of <35% causes increased result.
Blood samples in which serum is not separated from blood cells show glucose values decreasing at rate of 3 " 5% per hour at room temperature.
Postprandial capillary glucose is ≤36 mg/dL higher than venous glucose at peak of 1 hour postprandial; usually returns to negligible fasting difference within 4 hours, but in approximately 15% of patients, there may still be >20 mg/dL difference.
Low oxygen content (e.g., venous blood, high altitudes >3,000 m) gives falsely increased values.
Strenuous exercise, strong emotions, shock, burns, and infections can increase glucose physiologically.

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