C-Peptide

The connecting peptide, or C-peptide, is a short 31-amino-acid polypeptide that connects insulin's A-chain to its B-chain in the proinsulin molecule, releasing C-peptide and insulin from the pancreas at the same time and in about equal amounts.

So a C-peptide test can show how much insulin your body is making.

This test can be an excellent way to measure insulin levels because C-peptide tends to stay in the body longer than insulin.

A C-peptide test can help tell the difference between type 1 and type 2 diabetes. With type 1 diabetes, your pancreas makes little to no insulin and little or no C-peptide. With type 2 diabetes, the body produces insulin but doesn't use it well, which can cause C-peptide levels to be higher than usual.

The performance data of the C-P Rapid Quantitative Test Kit(CLIA)

Manufacturer	SEKBIO
Parameter	C-P
Linearity	0.01-40 ng/ml
Detection limit	0.01 ng/ml
benchmark product	Roche
Test principle and procedure	C-P: Add 15 μl of sample + 30 μl of Rd+30 μl of Raincubation for 15 minutes. Wash with 200 μl of washing solution. Finally, add 100 μl of A + 100 μl of B.

Six point calibration test results

Sample Concentration( ng/ml )	RLU			Average	CV	S/N
39.09	2,868,141	2,984,878	2,920,778	2,924,599	2.00%	3851.54
20.61	1,635,030	1,709,528	1,595,685	1,646,748	3.51%	2168.68
5.14	335,216	337,270	351,423	341,303	2.59%	449.48
0.47	17,622	17,873	17,701	17,732	0.72%	23.35
0.04	1,511	1,473	1,566	1,517	3.08%	2.00
0.00	764	755	759	759	0.59%	1.00

Precision

Sample	RLU	Concentration	Sample	RLU	Concentration
0.5	18,399	0.49	20	1,680,161	21.03
	17,298	0.46		1,646,289	20.60
	17,366	0.47		1,624,950	20.34
	18,393	0.49		1,636,695	20.48
	17,898	0.48		1,683,839	21.08
	18,312	0.49		1,686,358	21.11
	18,445	0.49		1,693,393	21.20
	18,105	0.48		1,668,111	20.88
	18,566	0.49		1,698,111	21.26
	18,330	0.49		1,687,107	21.12
AVE	18111.20	0.48	AVE	1,670,501	20.91
SD	451.02	0.01	SD	25591.77	0.32
CV	2.49%	2.08%	CV	1.53%	1.54%

Limit of detection

Sample	RLU		Concentration
Ag Diluent	814	825	0	0
	945	817	0.006	0
	743	783	0	0
	805	822	0	0
	779	835	0	0
	804	555	0	0
	791	855	0	0
	701	791	0	0
	827	605	0	0
	831	770	0	0
AVE	784.90		0.00
SD	84.89		0.00
AVE+2*SD	0.003

Linear

Sample（ng/ml)	Dilution ratio	Concentration value			Average
38.89	1.0	39.204	39.22	38.251	38.89
31.12	0.8	33.451	33.539	33.717	33.57
23.35	0.6	26.043	25.641	26.05	25.91
15.58	0.4	17.691	18.047	18.199	17.98
7.81	0.2	9.627	9.899	9.804	9.78
0.04	0.0	0.041	0.04	0.044	0.04

Method Comparison

Reagents Stability

Reagent	Sample( ng/ml)	Average	Deviation
2-8°	40.00	2,673,041
	5.00	305,357
	0.50	16,436
	0.00	683
37℃ 1d	40.00	2,524,613	-5.55%
	5.00	286,392	-6.21%
	0.50	14,671	-10.74%
	0.00	509	-25.55%
37℃ 4d	40.00	2,413,430	-9.71%
	5.00	287,230	-5.94%
	0.50	14,213	-13.53%
	0.00	351	-48.68%
37℃ 7d	40.00	2,338,396	-12.52%
	5.00	272,902	-10.63%
	0.50	13,926	-15.27%
	0.00	306	-55.20%

Calibrator Stability

Reagent	Sample(ng/ml)	Average	Deviation
2-8℃	20.00	3,979,931
2-8℃	0.20	19,627
37℃ 1d	20.00	4,009,219	0.74%
37℃ 1d	0.20	19,241	-1.97%
37℃ 4d	20.00	4,094,036	2.87%
37℃ 4d	0.20	19,275	-1.80%
37℃ 7d	20.00	3,964,933	-0.38%
37℃ 7d	0.20	18,882	-3.80%

C-Peptide Products

Antibody	Application
Mouse Anti-human C-Peptide mAb	For immunodiagnostic: ELISA, LFA, CLIA

C-Peptide Product Diagnostic Performance

C-Peptide Intro

C-peptide (C-Peptide), also known as a connecting peptide, is secreted by pancreatic beta cells, and it shares a common precursor with insulin, proinsulin. Proinsulin is split into one molecule of insulin and one molecule of C-peptide, so the molar amount of C-peptide and self-insulin is the same. Because the liver does not readily degrade C-peptide, C-peptide is the measurement of insulin content, accurately reflecting the function of islet cells. Blood can be drawn during the oral glucose tolerance test to measure the serum C-peptide level 1 hour, 2 hours, and 3 hours after fasting blood glucose load. The C-peptide level of ordinary people increased to more than three times the basal level after 60 minutes of glucose intake. The level of C-peptide in type 1 diabetes is deficient, and the postprandial C-peptide rise in patients with islet dysfunction is often less than 3-fold. For patients receiving insulin therapy, the auto-islet function cannot be evaluated by measuring insulin levels in the blood. Still, auto-islet β-cell function can assess by measuring C-peptide levels.

C-Peptide Test

C-peptide can reflect the secretory function of islet β cells in the body and has guiding significance for the classification of diabetic patients and the identification of hypoglycemia.

1. Diabetes

Determination of C-peptide levels can be applied to type diabetes and to understand the function of islet β cells in diabetic patients. Patients with type 1 or type 2 diabetes mellitus should detect the level of C-peptide or insulin to determine islet β-cell function at the beginning of the disease.

2. Hypoglycemia

When hypoglycemia occurs in a patient suspected of having insulinoma, measuring the blood glucose to insulin ratio can help diagnose. While hypoglycemia occurs in patients treated with exogenous insulin, determination of C-peptide can identify the cause of hypoglycemia.

3. Islet transplantation

In addition to monitoring blood glucose, C-peptide should be measured to understand the secretory function of islet β cells after transplantation.

4. Liver and kidney disease

When suffering from hepatitis or cirrhosis, the hepatic uptake of insulin decreases, and the level of insulin in the blood tends to increase. At the same time, the C-peptide is less affected by it, and the ratio of C-peptide to insulin in the blood decreases. When nephropathy occurs, the degradation of C-peptide slows down, the level of C-peptide in blood increases, and the ratio of C-peptide to insulin is significantly higher than usual.

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