fasting blood sugar
glu·cose tol·er·ance test (GTT),
fast·ing plas·ma glu·cose
(FPG) (fast'ing plaz'mă glū'kōs)Synonym(s): fasting blood sugar.
Glucose
Common use
Specimen
Serum (1 mL) collected in a gold-, red-, or red/gray-top tube, although plasma is recommended for diagnosis of diabetes. Plasma (1 mL) collected in a gray-top (sodium fluoride) or a green-top (heparin) tube.Normal findings
| Age | Conventional Units | SI Units (Conventional Units × 0.0555) |
|---|---|---|
| Fasting | ||
| Cord blood | 45–96 mg/dL | 2.5–5.3 mmol/L |
| Premature infant | 20–80 mg/dL | 1.1–4.4 mmol/L |
| Newborn 2 days–2 yr | 30–100 mg/dL | 1.7–5.6 mmol/L |
| Child | 60–100 mg/dL | 3.3–5.6 mmol/L |
| Adult-older adult | Less than 100 mg/dL | Less than 5.6 mmol/L |
| Prediabetes or impaired fasting glucose | 100–125 mg/dL | 5.6–6.9 mmol/L |
| 2-hr postprandial | 65–139 mg/dL | 3.6–7.7 mmol/L |
| Prediabetes or impaired 2-hr sample | 140–199 mg/dL | 7.8–11 mmol/L |
| Random | Less than 200 mg/dL | Less than 11.1 mmol/L |
Description
Diabetes is a group of diseases characterized by hyperglycemia, or elevated glucose levels. Hyperglycemia results from a defect in insulin secretion (type 1 diabetes), a defect in insulin action, or a combination of defects in secretion and action (type 2 diabetes). The chronic hyperglycemia of diabetes may result over time in damage, dysfunction, and eventually failure of the eyes, kidneys, nerves, heart, and blood vessels. The American Diabetes Association and National Institute of Diabetes and Digestive and Kidney Disease have established criteria for diagnosing diabetes to include any combination of the following findings or confirmation of any of the individual findings by repetition on a subsequent day:
- Symptoms of diabetes (e.g., polyuria, polydipsia, unexplained weight loss) in addition to a random glucose level greater than 200 mg/dL
- Fasting blood glucose greater than 126 mg/dL after a minimum of an 8-hr fast
- Glucose level greater than 200 mg/dL 2 hr after glucose challenge with standardized 75-mg load
| 1,5–Anhydroglucitol Measured Using the GlycoMark Assay | Hemoglobin A1c | Estimated Blood Glucose (mg/dL) | Degree of Diabetic Control |
|---|---|---|---|
| 14 mcg/mL or greater | 4–5% | 68–97 mg/dL | Normal/nondiabetic |
| 10–12 mcg/mL | 4–6% | 68–126 mg/dL | Well controlled |
| 5–10 mcg/mL | 6–8% | 126–183 mg/dL | Moderately well controlled |
| 2–5 mcg/mL | 8–10% | 183–240 mg/dL | Poorly controlled |
| Less than 2 mcg/mL | Greater than 10% (11–14%) | 269–355 mg/dL | Very poorly controlled |
Assessment of medications used to manage diabetes is an important facet of controlling the disease and its health-related complications. Drug response is an active area of study to ensure that the medications prescribed are meeting the needs of the patients who are taking them. Insulin and metformin are two commonly prescribed medications for the treatment of diabetes. See the “Insulin Antibodies” monograph for more detailed information. The AccuType Metformin Assay is a genetic test that identifies individuals who may not respond appropriately or have a suboptimal response to metformin related to a genetic mutation in the proteins responsible for transporting metformin.
This procedure is contraindicated for
- N/A
Indications
- Assist in the diagnosis of insulinoma
- Determine insulin requirements
- Evaluate disorders of carbohydrate metabolism
- Identify hypoglycemia
- Screen for diabetes
Potential diagnosis
Increased in
- Acromegaly, gigantism (growth hormone [GH] stimulates the release of glucagon, which in turn increases glucose levels)
- Acute stress reaction (hyperglycemia is stimulated by the release of catecholamines and glucagon)
- Cerebrovascular accident (possibly related to stress)
- Cushing’s syndrome (related to elevated cortisol)
- Diabetes (glucose intolerance and elevated glucose levels define diabetes)
- Glucagonoma (glucagon releases stored glucose; glucagon-secreting tumors will increase glucose levels)
- Hemochromatosis (related to iron deposition in the pancreas; subsequent damage to pancreatic tissue releases cell contents, including glucagon, resulting in hyperglycemia)
- Liver disease (severe) (damaged liver tissue releases cell contents, including stored glucose, into circulation)
- Myocardial infarction (related to stress and/or pre-existing diabetes)
- Pancreatic adenoma (damage to pancreatic tissue releases cell contents, including glucagon, resulting in hyperglycemia)
- Pancreatitis (acute and chronic) (damage to pancreatic tissue releases cell contents, including glucagon, resulting in hyperglycemia)
- Pancreatitis due to mumps (damage to pancreatic tissue releases cell contents, including glucagon, resulting in hyperglycemia)
- Pheochromocytoma (related to increased catecholamines, which increase glucagon; glucagon increases glucose levels)
- Renal disease (severe) (glucagon is degraded by the kidneys; when damaged kidneys cannot metabolize glucagon, glucagon levels in blood rise and result in hyperglycemia)
- Shock, trauma (hyperglycemia is stimulated by the release of catecholamines and glucagon)
- Somatostatinoma (somatostatin-producing tumor of pancreatic delta cells, associated with diabetes)
- Strenuous exercise (hyperglycemia is stimulated by the release of catecholamines and glucagon)
- Syndrome X (metabolic syndrome) (related to the development of diabetes)
- Thyrotoxicosis (related to loss of kidney function)
- Vitamin B1 deficiency (thiamine is involved in the metabolism of glucose; deficiency results in accumulation of glucose)
Decreased in
- Acute alcohol ingestion (most glucose metabolism occurs in the liver; alcohol inhibits the liver from making glucose) Addison’s disease (cortisol affects glucose levels; insufficient levels of cortisol result in diminished glucose levels) Ectopic insulin production from tumors (adrenal carcinoma, carcinoma of the stomach, fibrosarcoma) Excess insulin by injection Galactosemia (inherited enzyme disorder that results in accumulation of galactose in excessive proportion to glucose levels) Glucagon deficiency (glucagon controls glucose levels; hypoglycemia occurs in the absence of glucagon) Glycogen storage diseases (deficiencies in enzymes involved in conversion of glycogen to glucose) Hereditary fructose intolerance (inherited disorder of fructose metabolism; phosphates needed for intermediate steps in gluconeogenesis are trapped from further action by the enzyme deficiency responsible for fructose metabolism) Hypopituitarism (decreased levels of hormones such as adrenocorticotropin hormone [ACTH] and GH result in decreased glucose levels) Hypothyroidism (thyroid hormones affect glucose levels; decreased thyroid hormone levels result in decreased glucose levels) Insulinoma (the function of insulin is to decrease glucose levels) Malabsorption syndromes (insufficient absorption of carbohydrates) Maple syrup urine disease (inborn error of amino acid metabolism; accumulation of leucine is believed to inhibit the rate of gluconeogenesis, independently of insulin, and thereby diminish release of hepatic glucose stores) Poisoning resulting in severe liver disease (decreased liver function correlates with decreased glucose metabolism) Postgastrectomy (insufficient intake of carbohydrates) Starvation (insufficient intake of carbohydrates) von Gierke’s disease (most common glycogen storage disease; G6PD deficiency)
Critical findings
- Adults & children
- Less than 40 mg/dL (SI: Less than 2.22 mmol/L)
- Greater than 400 mg/dL (SI: Greater than 22.2 mmol/L)
- Newborns
- Less than 32 mg/dL (SI: Less than 1.8 mmol/L)
- Greater than 328 mg/dL (SI: Greater than 18.2 mmol/L)
Consideration may be given to verify the critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid Point of Care instrument at the bedside.
Note and immediately report to the health-care provider (HCP) any critically increased or decreased values and related symptoms.
It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.
Timely notification of critical values for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical value may require completion of a notification form with review by Risk Management.
Glucose monitoring is an important measure in achieving tight glycemic control. The enzymatic GDH-PQQ test method may produce falsely elevated results in patients who are receiving products that contain other sugars (e.g., oral xylose, parenterals containing maltose or galactose, and peritoneal dialysis solutions that contain icodextrin). The GDH-NAD, glucose oxidase, and glucose hexokinase methods can distinguish between glucose and other sugars.
Symptoms of decreased glucose levels include headache, confusion, hunger, irritability, nervousness, restlessness, sweating, and weakness. Possible interventions include oral or IV administration of glucose, IV or intramuscular injection of glucagon, and continuous glucose monitoring.
Symptoms of elevated glucose levels include abdominal pain, fatigue, muscle cramps, nausea, vomiting, polyuria, and thirst. Possible interventions include subcutaneous or IV injection of insulin with continuous glucose monitoring.
Glucose
Interfering factors
- Drugs that may increase glucose levels include acetazolamide, alanine, albuterol, anesthetic agents, antipyrine, atenolol, betamethasone, cefotaxime, chlorpromazine, chlorprothixene, clonidine, clorexolone, corticotropin, cortisone, cyclic AMP, cyclopropane, dexamethasone, dextroamphetamine, diapamide, epinephrine, enflurane, ethacrynic acid, ether, fludrocortisone, fluoxymesterone, furosemide, glucagon, glucocorticoids, homoharringtonine, hydrochlorothiazide, hydroxydione, isoniazid, maltose, meperidine, meprednisone, methyclothiazide, metolazone, niacin, nifedipine, nortriptyline, octreotide, oral contraceptives, oxyphenbutazone, pancreozymin, phenelzine, phenylbutazone, piperacetazine, polythiazide, prednisone, quinethazone, reserpine, rifampin, ritodrine, salbutamol, secretin, somatostatin, thiazides, thyroid hormone, and triamcinolone.
- Drugs that may decrease glucose levels include acarbose, acetylsalicylic acid, acipimox, alanine, allopurinol, antimony compounds, arsenicals, ascorbic acid, benzene, buformin, cannabis, captopril, carbutamide, chloroform, clofibrate, dexfenfluramine, enalapril, enprostil, erythromycin, fenfluramine, gemfibrozil, glibornuride, glyburide, guanethidine, niceritrol, nitrazepam, oral contraceptives, oxandrolone, oxymetholone, phentolamine, phosphorus, promethazine, ramipril, rotenone, sulfonylureas, thiocarlide, tolbutamide, tromethamine, and verapamil.
- Elevated urea levels and uremia can lead to falsely elevated glucose levels.
- Extremely elevated white blood cell counts can lead to falsely decreased glucose values.
- Administration of insulin or oral hypoglycemic agents within 8 hr of a fasting blood glucose can lead to falsely decreased values.
- Specimens should never be collected above an IV line because of the potential for dilution when the specimen and the IV solution combine in the collection container, falsely decreasing the result. There is also the potential of contaminating the sample with the substance of interest, if it is present in the IV solution, falsely increasing the result.
- Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated; failure to follow dietary restrictions before the fasting test can lead to falsely elevated glucose values.
Nursing Implications and Procedure
Potential nursing problems
| Problem | Signs & Symptoms | Interventions |
|---|---|---|
| Blood glucose (Related to sedentary lifestyle, circulating insulin deficiency secondary to pancreatic insufficiency; excessive dietary intake; insulin resistance) | Excess: Fatigue; mild dehydration; elevated blood glucose; weight loss; weakness; polyuria; polydipsia; polyphagia; blurred vision; headache; paresthesia; poor skin turgor; dry mouth; nausea; vomiting; abdominal pain; Kussmaul respirations. Deficit: tremor, sweating, decreased concentration; diaphoresis; elevated blood pressure; palpitations; headache; hunger; restlessness; lethargy; altered mental status; combativeness; altered speech; altered coordination | Check blood glucose before meals and at bedtime; administer prescribed insulin or oral agents; educate and encourage the patient to participate in glucose self-check and record results; assess readiness to learn and barriers to learning; collaborate with the health-care provider and dietician to support medical nutritional therapy; refer to dietician to assist the patient to select appropriate cultural foods; develop a plan of exercise commensurate with the patient’s physical abilities; discuss lifestyle alterations necessary to support positive health management secondary to disease process; teach good hygiene and infection prevention; monitor laboratory studies that may be impacted by altered glucose and trend results (HGB A1C; BUN; Cr; electrolytes; arterial pH; magnesium; urine ketones; urine microalbumin; WBC; amylase; HGB/HCT; C-reactive protein; liver enzymes); facilitate oral hydration; correlate blood glucose with other laboratoryvalues and medical condition(s); address the psychosocial aspects of the disease; monitor serum insulin levels |
| Infection risk (Related to altered blood glucose; exposure to opportunistic hosts; poor personal hygiene; broken skin; wound presence) | Increased temperature; increased heart rate and respiratory rate; chills; change in mental status; fatigue; malaise; weakness; anorexia; headache; nausea; elevated blood glucose; hypotension; diminished oxygen saturation; elevated WBC; elevated C-reactive protein | Provide standard precautions in the provision of care; correlate symptoms with laboratory values and disease process; trend vital signs and laboratory values to monitor for improvement; administer prescribed antibiotics and medications for fever reduction; provide cooling measures; ensure vigilant hand hygiene; educate patient and family regarding good hand hygiene; infuse ordered IV fluids to support adequate hydration; ensure implementation of infection prevention measures with consideration of age and culture such as adequate nutrition; provide aseptic wound care; ensure good skin care; ensure good oral care; ensure adequate rest; instruct patient to avoid exposure to opportunistic hosts; send cultures to the laboratory as ordered; correlate culture findings with selected antibiotics |
| Noncompliance (Related to refusal to accept new diagnosis; financial instability; cultural norms; complexity of the medical management; lack of knowledge) | Insufficient disease management; alterations in blood glucose; poor self-management of medication administration; lack of supplies to support self-management; poor dietary control with inappropriate food selections | Assess the patient’s ability to and prior efforts to manage the disease process; evaluate the ability to self-manage the disease including blood glucose screening, dietary management, exercise, and medication self-administration; assess for personal factors that may limit the patient’s ability to self-perform such as visual, cognitive, and hearing; assess the financial ability to purchase the medication and supplies necessary to provide self-care; assess the level of family support; ensure the patient has the adequate knowledge to perform self-care and if not provide the necessary training; ensure the patient knows the signs and symptoms related to the disease process; teach correct dietary selections meeting cultural- and age-appropriate needs; refer to social services or home health; discuss how to manage diabetes during travel |
| Nutrition(Related to excessive dietary intake more than body requirements, insulin deficiency, stress; anxiety; depression; cultural lifestyle; unhealthy food sources; financial restrictions) | Increased thirst, increased urination, weight loss; fatigue; elevated blood glucose levels; inadequate glucose management; increased hunger | Monitor blood glucose results, refer to dietician for evaluation, administer insulin or oral agent; assess the cultural aspects of diet selection; correlate dietary intake with blood glucose and monitor trends; collaborate with a dietician to develop a cultural- and age-appropriate diet plan; correlate nutritional intake and exercise; ensure that the patient understands the relationship between caloric intake and medication (insulin, oral agent); refer to social services and dietitian as necessary |
Pretest
- Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
- Patient Teaching: Inform the patient this test can assist in evaluating blood sugar levels.
- Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
- Obtain a history of the patient’s endocrine system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
- Obtain a list of medications the patient is taking, including herbs, nutritional supplements, nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus), insulin, and any other substances used to regulate glucose levels.
- Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
- Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
- Instruct the patient to fast for at least 12 hr before specimen collection for the fasting glucose test.
- Instruct the patient to follow the instructions given for 2-hr postprandial glucose test. Some HCPs may order administration of a standard glucose solution, whereas others may instruct the patient to eat a meal with a known carbohydrate composition.
Intratest
- Potential complications: N/A
- Ensure that the patient has complied with dietary restrictions and other pretesting preparations; assure that food has been restricted for at least 12 hr prior to the fasting procedure.
- Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
- Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
- Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
- Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
- Promptly transport the specimen to the laboratory for processing and analysis.
Post-Test
- Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
- Instruct the patient to resume usual diet, as directed by the HCP.
- Nutritional Considerations: Increased glucose levels may be associated with diabetes. There is no “diabetic diet”; however, many meal-planning approaches with nutritional goals are endorsed by the American Dietetic Association. Patients who adhere to dietary recommendations report a better general feeling of health, better weight management, greater control of glucose and lipid values, and improved use of insulin. Instruct the patient, as appropriate, in nutritional management of diabetes. The 2013 Guideline on Lifestyle Management to Reduce Cardiovascular Risk published by the American College of Cardiology (ACC) and the American Heart Association (AHA) in conjunction with the National Heart, Lung, and Blood Institute (NHLBI) recommends a “Mediterranean”-style diet rather than a low-fat diet. The new guideline emphasizes inclusion of vegetables, whole grains, fruits, low-fat dairy, nuts, legumes, and nontropical vegetable oils (e.g., olive, canola, peanut, sunflower, flaxseed) along with fish and lean poultry. A similar dietary pattern known as the Dietary Approaches to Stop Hypertension (DASH) diet makes additional recommendations for the reduction of dietary sodium. Both dietary styles emphasize a reduction in consumption of red meats, which are high in saturated fats and cholesterol, and other foods containing sugar, saturated fats, trans fats, and sodium. If triglycerides also are elevated, the patient should be advised to eliminate or reduce alcohol. The nutritional needs of each diabetic patient need to be determined individually (especially during pregnancy) with the appropriate HCPs, particularly professionals trained in nutrition.
- Social and Cultural Considerations: Numerous studies point to the prevalence of excess body weight in American children and adolescents. Experts estimate that obesity is present in 25% of the population ages 6 to 11 yr. The medical, social, and emotional consequences of excess body weight are significant. Special attention should be given to instructing the child and caregiver regarding health risks and weight control education.
- Recognize anxiety related to test results, and be supportive of perceived loss of independence and fear of shortened life expectancy. The ADA recommends A1C testing 4 times a year for insulin-dependent type 1 or type 2 diabetes and twice a year for non–insulin-dependent type 2 diabetes. The ADA also recommends that testing for diabetes commence at age 45 for asymptomatic individuals, be considered for adults of any age who are overweight and have additional risk factors, and continue every 3 yr in the absence of symptoms.
- Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
Patient Education
- Instruct the patient and caregiver to report signs and symptoms of hypoglycemia (weakness, confusion, diaphoresis, rapid pulse) or hyperglycemia (thirst, polyuria, hunger, lethargy).
- Discuss the implications of abnormal test results on the patient’s lifestyle.
- Provide teaching and information regarding the clinical implications of the test results, as appropriate.
- Emphasize, if indicated, that good glycemic control delays the onset and slows the progression of diabetic retinopathy, nephropathy, and neuropathy.
- Educate the patient regarding access to counseling services, as appropriate.
- Provide contact information, if desired, for the American Diabetes Association (ADA; www.diabetes.org) or the AHA (www.americanheart.org) or the NHLBI (www.nhlbi.nih.gov).
- Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
- Instruct the patient in the use of home test kits approved by the U.S. Food and Drug Administration, if prescribed.
- Answer any questions or address any concerns voiced by the patient or family.
- Teach the patient and family the signs and symptoms of hyperglycemia and hypoglycemia.
Expected Patient Outcomes
- Knowledge
- States understanding of the signs and symptoms that could indicate an infection
- States understanding of the value of good glucose management to their overall health and longevity.
- Skills
- Demonstrates proficiency in the ability to perform accurate self-check glucose checks.
- Demonstrates proficiency in the ability to perform insulin self-administration correctly or to take oral agent.
- Attitude
- Complies with the medication management recommended by the health-care provider.
- Complies with dietary restrictions.
Related Monographs
- Related tests include ACTH, angiography adrenal, BUN, calcium, catecholamines, cholesterol (HDL, LDL, total), cortisol, C-peptide, CT cardiac scoring, CRP, CK and isoenzymes, creatinine, DHEA, echocardiography, fecal analysis, fecal fat, fluorescein angiography, fructosamine, fundus photography, gastric emptying scan, glucagon, GTT, glycated hemoglobin A1C, gonioscopy, Holter monitor, HVA, insulin, insulin antibodies, ketones, LDH and isoenzymes, lactic acid, lipoprotein electrophoresis, MRI chest, metanephrines, microalbumin, myoglobin, MI infarct scan, myocardial perfusion heart scan, plethysmography, PET heart, renin, sodium, troponin, and visual fields test.
- Refer to the Endocrine System table at the end of the book for related tests by body system.