Type of test Blood

Normal findings

Fasting: 0.78-1.89 ng/mL or 0.26-0.62 nmol/L (SI units)

1 hour after glucose load: 5-12 ng/mL

 Test explanation and related physiology

 In general, C-peptide levels correlate with insulin levels in the blood. The capacity of the pancreatic beta cells to secrete insulin can be evaluated by directly measuring either insulin or C-peptide. In most cases, direct measurement of insulin is more accurate. C-peptide levels, however, more accurately reflect islet cell function in the following situations:

• Patients with diabetes who are treated with exogenous insulin and who have antiinsulin antibodies.

• Patients who secretly administer insulin to themselves (factitious hypoglycemia). Insulin levels will be elevated. Direct insulin measurement in these patients tends to be high because the insulin measured is the self-administered exogenous insulin. But C-peptide levels in that same specimen will be low because exogenously administered insulin suppresses endogenous insulin (and C-peptide) production.

 • Patients with diabetes who are taking insulin. This is done to see if the patient with diabetes is in remission and may not need exogenous insulin.

• Distinguishing type I from type 2 diabetes. This is particularly helpful in people who are newly diagnosed with diabetes. A person whose pancreas does not make any insulin (type 1 diabetes) has low levels of insulin and C-peptide. A person with type 2 diabetes has a normal or high level of C-peptide.

Furthermore, C-peptide is used in evaluating patients who are suspected of having an insulinoma. In patients with an autonomous secreting insulinoma, C-peptide levels are high. C-peptide can also be used to monitor treatment for insulinoma. A rise in C-peptide levels indicates a recurrence or progression of the insulinoma. In the same way, clinicians use C-peptide testing as an indicator of the adequacy of therapeutic surgical pancreatectomy in patients with pancreatic tumors. C-peptide can also be used to diagnose insulin resistance syndrome and to measure beta cell function after glucagon stimulation.

Interfering factors

 • Because the majority of C-peptide is degraded in the kidney, renal failure can cause increased levels.

* Drugs that may cause increased levels of C-peptide include oral hypoglycemic agents (e.g., sulfonylureas).

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

• Fasting: yes

• Blood tube commonly used: red

Abnormal findings

Increased levels

- Insulinoma

- Renal failure

- Pancreas transplant

- Type 2 diabetes mellitus

Decreased levels

- Factitious hypoglycemia

- Radical pancreatectomy

- Type 1 diabetes mellitus

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مواضيع ذات صلة

Laboratory Diagnosis of Urinary Tract Infections

Identification of Mycoplasma Infections

Laboratory Diagnosis of Infections of the Eyes

Laboratory Diagnosis of Central Nervous System Infections

Diagnosis and Differential Diagnosis of Paroxysmal Nocturnal Hemoglobinuria

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Diagnosis of Upper Respiratory Tract Infections

tuberculosis testing (TB testing, Interferon gamma release assay [IGRA, T-Spot.TB], QuantiFERON-TB Gold [QFT, QFT-G, TB Gold test, TB blood test], Nucleic acid amplification for TB [NAAT], TB antibody)

thyrotropin-releasing hormone stimulation test (TRH stimulation test, Thyrotropin-releasing factor stimulation test [TRF stimulation test])

Laboratory Diagnosis of Lower Respiratory Tract Infections: Specimen Processing

Laboratory Diagnosis of Lower Respiratory Tract Infections: Specimen Collection and Transport