Insulin and Insulin Response to Glucose

Synonym/acronym: N/A.

Common use

To assess the amount of insulin secreted in response to blood glucose to assist in diagnosis of types of hypoglycemia and insulin-resistant pathologies.

Specimen

Serum (1 mL) collected in a red-top tube.

Normal findings

(Method: Immunoassay)

75-g Glucose Load	Insulin	SI Units (Conventional Units × 6.945)	Tolerance for Glucose (Hypoglycemia)
Fasting	Less than 17 micro international units/L	Less than 118.1 pmol/L	Less than 110 mg/dL
30 min	6–86 micro international units/L	41.7–597.3 pmol/L	Less than 200 mg/dL
1 hr	8–118 micro international units/L	55.6–819.5 pmol/L	Less than 200 mg/dL
2 hr	5–55 micro international units/L	34.7–382 pmol/L	Less than 140 mg/dL
3 hr	Less than 25 micro international units/L	Less than 174 pmol/L	65–120 mg/dL
4 hr	Less than 15 micro international units/L	Less than 104.2 pmol/L	65–120 mg/dL
5 hr	Less than 8 micro international units/L	Less than 55.6 pmol/L	65–115 mg/dL

Description

Insulin is a hormone secreted by the beta cells of the islets of Langerhans in the pancreas in response to elevated blood glucose levels. It’s overall effect is to help regulate the metabolism of glucose. Specifically, insulin decreases blood levels of glucose by promoting transport of glucose into the liver and muscles to be stored as glycogen. Insulin also participates in regulation of the processes required for metabolism of fats, carbohydrates, and proteins. The insulin response test measures insulin response to a standardized dose of glucose, administered over fixed period of time and is useful in evaluating patients with hypoglycemia and suspected insulin-resistance.

This procedure is contraindicated for

N/A

Indications

Assist in the diagnosis of early or developing non–insulin-dependent (type 2) diabetes, as indicated by excessive production of insulin in relation to blood glucose levels (best shown with glucose tolerance tests or 2-hr postprandial tests)
Assist in the diagnosis of insulinoma, as indicated by sustained high levels of insulin and absence of blood glucose–related variations
Confirm functional hypoglycemia, as indicated by circulating insulin levels appropriate to changing blood glucose levels
Differentiate between insulin-resistant diabetes, in which insulin levels are high, and non–insulin-resistant diabetes, in which insulin levels are low
Evaluate fasting hypoglycemia of unknown cause
Evaluate postprandial hypoglycemia of unknown cause
Evaluate uncontrolled insulin-dependent (type 1) diabetes

Potential diagnosis

Increased in

Acromegaly (related to excess production of growth hormone, which increases insulin levels)
Alcohol use (related to stimulation of insulin production)
Cushing’s syndrome (related to overproduction of cortisol, which increases insulin levels)
Excessive administration of insulin
Insulin- and proinsulin-secreting tumors (insulinomas)
Obesity (related to development of insulin resistance; body does not respond to insulin being produced)
Persistent hyperinsulinemic hypoglycemia (collection of hypoglycemic disorders of infants and children)
Reactive hypoglycemia in developing diabetes
Severe liver disease

Decreased in

(pancreatic beta cells produce insulin; therefore, damage to these cells will decrease insulin levels)

(related to lack of endogenous insulin)

Critical findings

N/A

Interfering factors

Drugs and substances that may increase insulin levels include acetohexamide, albuterol, amino acids, beclomethasone, betamethasone, broxaterol, calcium gluconate, cannabis, chlorpropamide, glibornuride, glipizide, glisoxepide, glucagon, glyburide, ibopamine, insulin, oral contraceptives, pancreozymin, prednisolone, prednisone, rifampin, terbutaline, tolazamide, tolbutamide, trichlormethiazide, and verapamil.
Drugs that may decrease insulin levels include acarbose, calcitonin, cimetidine, clofibrate, dexfenfluramine, diltiazem, doxazosin, enalapril, enprostil, ether, hydroxypropyl methylcellulose, metformin (Glucophage), niacin, nifedipine, nitrendipine, octreotide, phenytoin, propranolol, and psyllium.
Administration of insulin or oral hypoglycemic agents within 8 hr of the test can lead to falsely elevated levels.
Hemodialysis destroys insulin and affects test results.

Nursing Implications and Procedure

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 the evaluation of low blood sugar.
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.
Note any recent procedures that can interfere with test results.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Note the last time and dose of medication taken.
Review the procedure with the patient. Inform the patient that multiple specimens may be required. 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.
If a single sample is to be collected, the patient should have fasted and refrained, with medical direction, from taking insulin or other oral hypoglycemic agents for at least 8 hr before specimen collection. Protocols may vary among facilities.
Hypoglycemia: Serial specimens for insulin levels are collected in conjunction with glucose levels after administration of a 75-g glucose load. The patient should be prepared as for a standard oral glucose tolerance test over a 5-hr period. Protocols may vary among facilities.
Note that there are no fluid restrictions unless by medical direction.

Intratest

Potential complications:
Note that the patient may have difficulty drinking the extremely sweet glucose beverage and become nauseous.
Ensure that the patient has complied with dietary and medication restrictions and other pretesting preparations; assure that food or medications have been restricted as instructed prior to the specific procedure’s protocol.
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 health-care provider (HCP), who will discuss the results with the patient.
Instruct the patient to resume usual diet and medication, as directed by the HCP.
Nutritional Considerations: 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.
Note that abnormal insulin response and impaired glucose tolerance may be associated with diabetes. Instruct the patient and caregiver to report signs and symptoms of hypoglycemia (weakness, confusion, diaphoresis, rapid pulse) or hyperglycemia (thirst, polyuria, hunger, lethargy).
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. 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 (www.diabetes.org), the American Heart Association (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.
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. The American Diabetes Association (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 and continue every 3 yr in the absence of symptoms. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include ACTH, ALT, angiography adrenal, bilirubin, BUN, calcium, catecholamines, cholesterol (HDL, LDL, total), cortisol, C-peptide, DHEA, creatinine, fecal analysis, fecal fat, fructosamine, GGT, gastric emptying scan, glucagon, glucose, GTT, glycated hemoglobin, GH, HVA, insulin antibodies, ketones, lipoprotein electrophoresis, metanephrines, microalbumin, and myoglobin.
Refer to the Endocrine System table at the end of the book for related tests by body system.