Synonym/Acronym
Connecting peptide insulin, insulin C-peptide, proinsulin C-peptide.
Rationale
To evaluate hypoglycemia, assess beta cell function, and monitor insulin production.
Patient Preparation
There are no fluid, activity, or medication restrictions unless by medical direction. Instruct the patient to fast for at least 10 hr before specimen collection. Protocols may vary among facilities.
Normal Findings
Method: Immunochemiluminometric assay (ICMA).
| Age | Conventional Units | SI Units (Conventional Units × 0.333) |
|---|
| Child | 0–3.3 ng/mL | 0–1.1 nmol/L | | Adult | 0.8–3.5 ng/mL | 0.3–1.2 nmol/L | | 1-hr response to glucose | 2.3–11.8 ng/mL | 0.8–3.9 nmol/L |
|
Study type: Blood collected in a red-top tube; related body system: Endocrine system.
C-peptide is a biologically inactive peptide formed when beta cells of the pancreas convert proinsulin to insulin. C-peptide levels provide a reliable indication of how well the pancreatic beta cells secrete insulin. Therefore, C-peptide and insulin levels normally correlate. Most of C-peptide is excreted by the kidneys. Release of C-peptide is not affected by exogenous insulin administration, and levels can assist the health-care provider (HCP) to determine when to begin treatment with insulin.
C-peptide values increase after stimulation with glucose or glucagon, and measurement of C-peptide levels are very useful in the evaluation of hypoglycemia. An insulin/C-peptide ratio of 1 or less indicates endogenous insulin secretion, whereas a ratio greater than 1 indicates an excess of exogenous insulin. For additional information regarding screening guidelines and management of diabetes refer to the study titled “Glucose Core Lab Study.”
Factors That May Alter the Results of the Study
- Drugs and other substances that may increase C-peptide levels include chloroquine, corticosteroids (betamethasone, prednisone), danazol, deferoxamine, indapamide, oral contraceptives, rifampin, and sulfonylureas.
- Drugs and other substances that may decrease C-peptide levels include atenolol and calcitonin.
Other Considerations
- C-peptide and endogenous insulin levels do not always correlate in obese patients.
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assist in assessing for low blood sugar.
- Explain that a blood sample is needed for the test.
After the Study: Implementation & Evaluation Potential Nursing Actions
Avoiding Complications
- Stress how good glucose level management delays the onset and slows the progression of diabetic retinopathy, nephropathy, and neuropathy.
- Discuss how unmanaged diabetes can cause multiple health issues, including chronic kidney disease, limb amputation, and ultimately death.
- Emphasize the importance of adhering to the HCP recommended therapeutic regime to manage diabetes.
- Examine the advantages of support group attendance to learn how to successfully manage diabetes.
Treatment Considerations
Hypoglycemia
- Discuss symptoms of hypoglycemia: elevated heart rate, dizziness, tremor, fatigue, hunger, visual changes, headache, weakness, agitation, clammy skin, pale skin, shakiness, tingling lips and tongue, anxiety, seizures, loss of consciousness.
- Explain that hypoglycemia is defined as a blood glucose less than 70 mg/dL.
- Discuss how eating frequently can help decrease incidence of hypoglycemia.
- Discuss how increased activity can contribute to hypoglycemia.
- Discuss some causes of hypoglycemia: diabetic medications; substance use disorder (alcohol); severe illness such as hepatitis, cirrhosis, and renal disease; insulin overproduction; or adrenal and pituitary disease.
Hyperglycemia
- Discuss symptoms of hyperglycemia: thirst, glycosuria, confusion, increased urination, fatigue, blurred vision, headache, fruity smelling breath, weakness, coma, shortness of breath, nausea and vomiting, dry mouth, abdominal pain.
- Explain that hyperglycemia is generally defined as a glucose level greater than 200 mg/dL.
- Discuss risk factors for developing hyperglycemia: illness, infection, surgery, stress, conflict, inactivity, incorrect use of insulin or oral medication, not following diet guidelines.
- Encourage prevention strategies that include following medication and diet guidelines, with accurate glucose monitoring.
Nutritional Considerations
- Provide education on the nutritional management of diabetes.
- Encourage consultation with a registered dietitian who is a certified diabetes educator.
- Increased levels of C-peptide may be associated with diabetes.
- Discuss how there is no “diabetic diet”; however, many meal-planning approaches with nutritional goals are endorsed by the American Diabetes Association.
- Discuss that a variety of dietary patterns are beneficial for people with diabetes.
- Explain that patients who adhere to dietary recommendations report a better general feeling of health, better weight management, greater management of glucose and lipid values, and improved use of insulin.
Clinical Judgement
- Consider the difficulty of changing diet and lifestyle to improve health and how to get buy in to achieve this goal.
Follow-Up and Desired Outcomes
- Acknowledges contact information provided for the American Heart Association (www.heart.org/HEARTORG), the National Heart, Lung, and Blood Institute (www.nhlbi.nih.gov), or the U.S. Department of Agriculture’s resource for nutrition (www.choosemyplate.gov).
- Demonstrates how to perform a self-check glucose accurately and to correctly self-administer insulin or to take oral antihyperglycemic drugs.
- Acknowledges that reporting signs and symptoms of hypoglycemia (weakness, confusion, diaphoresis, rapid pulse) or hyperglycemia (thirst, polyuria, hunger, lethargy) is essential to good glucose management.