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C-Peptide Suppression

Rationale: This test has been used in cases in which the 72-hour diagnostic fast is inconclusive.1,2Production of C-peptide by normal subjects is generally suppressed during hypoglycemia. The degree of C-peptide suppression is diminished in patients with insulinoma. Normative data, based on age and body mass index (BMI), are calculated as weight (kg) divided by the square of height in meters.2 The extent of suppression (as a percentage) of the 60-minute C-peptide concentration relative to the baseline sample should be ≥ the values tabulated as follows.

Age (y)

BMI (kg/m2)

20-24

25-29

30-34

20-29

67%

66%

65%

30-39

65%

64%

62%

40-49

63%

61%

59%

50-59

61%

59%

57%

60-69

59%

57%

54%

70-79

57%

54%

51%

Protocol: After an overnight fast, insulin (0.125 units/kg) should be infused over a period of 60 minutes. Blood should be collected for glucose and C-peptide measurements at baseline and 60 minutes.2

Orderable Tests: 143302 C-Peptide x2 (baseline, one-hour)

Note: Intravenous access should be maintained, and glucose should be available for infusion.

References

1. Service FJ. Diagnostic approach to adults with hypoglycemic disorders. Endocrinol Metab Clin North Am. 1999 Sep; 28(3):519-532. PubMed 10500929

2. Service FJ, O'Brien PC, Kao PC, Young WF Jr. C-peptide suppression test: Effects of gender age, and body mass index; Implications for the diagnosis of insulinoma. J Clin Endocrinol Metab. 1992 Jan; 74(1):204-210. PubMed 1727822

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