Human C-Peptide
117
SUMMARY AND EXPLANATION OF THE TEST
The connecting Peptide, or C-Peptide, is a short 31-amino-acid protein that connects insulin’s A-chain to its B-chain in the proinsulin molecule. Patients
with diabetes may have their C-Peptide levels measured as a means of distinguishing Type 1 diabetes from Type 2 diabetes or Maturity Onset Diabetes of
the Young (MODY). Serum C-Peptide levels correlate with endogenous insulin production and surviving β-cells and are present in equimolar amounts.
Ultrasensitive assays reveal C-Peptide production persists for decades after Type 1 disease onset and remains functionally responsive in patients with
advanced disease, whose β-cells function was thought to have ceased. C-Peptide levels are measured instead of insulin levels because C-Peptide can
assess a person’s own insulin secretion even if they receive insulin injections, and because the liver metabolizes a larger and variable amount of insulin
secreted into the portal vein but does not metabolize C-Peptide, which means that blood C-Peptide may be a better measure of portal insulin secretion
than insulin itself.
Median
[C-Peptide]
1,628 pg/mL
Median
[C-Peptide]
0.0860 pg/mL
Normal
plasma
Normal
Serum
Diabetic
Serum
C-Peptide, pg/mL
%CVdose
AEB
C-Peptide, pg/mL
C-Peptide, pg/mL
Figure 1: SimoaTM C-Peptide immunoassay
calibration curve. Four-parameter curve fit
parameters are depicted.
Median
[C-Peptide]
1,559 pg/mL
Figure 2: Simoa C-Peptide CV profile.
Diluted serum samples were assayed in reps
of 3 over multiple days (33 determinations).
Dose CVs are depicted.
Figure 3: [C-Peptide] in EDTA plasma (n = 12), matched
serum (n = 12), and serum from Type I diabetes patients
(n = 29). Of 38 Type I samples tested, 5 were unreadable
and 4 were >400 pg/mL. Error bars depict mean and SEM.
Table 1: General characteristics of Simoa Human C-Peptide immunoassay
Calibration range
0-100 pg/mL
Dynamic range1
0-400pg/mL
Lower limit of detection (2.5 SD from zero, n = 3 reps x 10 runs over 5 days, mean LoD2)
0.013 pg/mL
Lower limit of quantification (≤20% CVdose, see Figure 2)
0.021 pg/mL
Spike-recovery (C-Peptide spiked into 3 serum samples at 2 levels,
mean3)
103.0%
Linearity (high C-Peptide serum sample admixed with low C-Peptide sample, mean of 10 levels)
96.7%
Sample volume
25 µL
1Samples
auto-diluted 4X.
2SD
of LoD estimates 0.0125pg/mL.
3Range
The Simoa Human
C-Peptide immunoassay
reliably quantifies
C-Peptide in serum and
plasma in healthy
subjects, and in most
Type I diabetes subjects.
94.1-111.7%.
Table 2: Precision characteristics of Simoa Human C-Peptide immunoassay. Precision was determined
with guidance from CLSI Protocol EP5-A. Five samples consisting of three serum-based panels, and two C-Peptide
controls were assayed in replicates of three at two separate times per day for five days using a single lot of reagents
and calibrators. Analysis of variance (fully nested ANOVA) results are summarized in the following table.
Sample
Control 1
Control 2
Panel 11
Panel 12
Panel 22
1Auto-diluted
Mean C-Peptide
Within Run
Between Run
Between Day
(pg/mL)
%CV (n=30)
%CV (n=10)
%CV (n=5)
1.80
57.2
51.6
8.2
5.4
9.1
0.0
6.0
2.8
2.9
0.0
7.1
49.8
1830
3.1
4.4
2.6
2.5
1.1
4.3
4X. 2Pre-diluted 25X, followed by auto-dilution 4X (total 100X pre-dilution).
Assay designed by Erica
Simoa
HD-1 Analyzer
For Research Use Only. Not for use in diagnostic procedures.
USER-117-02 09JAN2015