Postprandial C-peptide is more relevant to hemoglobin A1c levels and diabetic microvascular complications than fasting C-peptide in type 2 diabetes

Table 1 Characteristics of the participants, n (%)

	n	Median (interquartile range or percent)	Range
Age (years)	453	62 (55, 68)	26-86
Sex (male)	453	273 (60.3)	—
Body mass index (kg/m2)	442	25.2 (23.0, 27.7)	15.8-42.3
Duration of diabetes (years)	453	12 (6, 19)	0.08-40
Hemoglobin A1c (%)	453	8.8 (7.3, 10.4)	5.5-16.7
FPG (mmol/L)	452	7.1 (5.7, 9.0)	3.2-22.7
Postprandial blood glucose (mmol/L)	447	11.8 (9.2, 14.9)	2.8-30.9
Total cholesterol (mmol/L)	451	4.16 (3.50, 4.97)	2.06-7.77
Triglyceride (mmol/L)	451	1.28 (0.97, 1.88)	0.4-18.32
Low-density lipoprotein cholesterol (mmol/L)	451	2.42 (1.81, 3.12)	0.55-5.48
High-density lipoprotein cholesterol (mmol/L)	451	1.06 (0.92, 1.29)	0.54-2.44
Creatinine (μmol/L)	453	63 (54, 76)	31-131
Uric acid (μmol/L)	451	335 (279, 395)	144-661
Alanine transaminase (mmol/L)	453	17 (14, 26)	1-119
FCP (pmol/L)	453	306.3 (190.6, 494.6)	2.9-1582.0
2hCP (pmol/L)	453	858.6 (480.5, 1324.6)	4.7-4652.7
Delta CP	453	484.5 (215.7, 895.7)	-291.1 to 3798.3
CP ratio	453	2.73 (1.75, 3.74)	0.22-437.82
FCP/FPG	452	42.33 (24.82, 65.19)	0.85-268.14
2hCP/postprandial blood glucose	447	66.10 (36.95, 114.83)	0.80-434.83
Delta CP/BG	446	23.03 (6.14, 51.79)	-132.93 to 301.60
CP/BG ratio	446	1.60 (1.18, 2.19)	0.26-265.48
Insulin treatment	453	268 (59.2)	—
OADs treatment	453	447 (98.7)	—
OADs and insulin treatment	453	195 (43.1)	—
Diabetes microvascular complications	453	372 (82.1)	—
Diabetic retinopathy	453	130 (28.7)	—
Diabetic peri-neuropathy	453	325 (71.7)	—
Diabetic kidney disease	453	151 (33.3)	—

Data are shown as median (interquartile ranges) or percentage (%). BG: Blood glucose; CP: C-peptide; FCP: Fasting C-peptide; FPG: Fasting plasma glucose; OADs: Oral anti-diabetic drugs; 2hCP: 2 hours postprandial C-peptide.

Table 2 Partial correlation between C-peptide and hemoglobin A1c

	r value	95%CI	P value
FCP	-0.168	-0.249 to -0.075	< 0.001
2hCP	-0.423	-0.480 to -0.362	< 0.001
Delta CP	-0.445	-0.503 to -0.388	< 0.001
CP ratio	-0.057	-0.309 to -0.008	0.23
FCP/ fasting plasma glucose	-0.346	-0.415 to -0.273	< 0.001
2hCP/postprandial blood glucose	-0.485	-0.551 to -0.414	< 0.001
Delta CP/BG	-0.428	-0.501 to -0.351	< 0.001
CP/BG ratio	-0.058	-0.320 to -0.048	0.222

BG: Blood glucose; CP: C-peptide; FCP: Fasting C-peptide; 2hCP: 2 hours postprandial C-peptide.

Table 3 Logistic regression of diabetic retinopathy

	Model 1		Model 2		Model 3
	OR (95%CI)	P value	OR (95%CI)	P value	OR (95%CI)	P value
FCP	0.999 (0.998-1)	0.005	0.999 (0.998-1)	0.185	0.999 (0.998-1)	0.243
2hCP	0.999 (0.999-1)	< 0.001	0.999 (0.999-1)	0.001	0.999 (0.999-1)	0.002
Delta CP	0.999 (0.999-1)	< 0.001	0.999 (0.999-1)	0.001	0.999 (0.999-1)	0.001
CP ratio	0.999 (0.989-1.009)	0.877	1 (0.989-1.011)	0.986	1 (0.989-1.011)	0.965
FCP/fasting plasma glucose	0.988 (0.981-0.995)	0.001	0.992 (0.984-0.999)	0.034	0.992 (0.984-1)	0.058
2hCP/postprandial blood glucose	0.991 (0.987-0.995)	< 0.001	0.993 (0.988-0.997)	0.001	0.991 (0.986-0.996)	0.001
Delta CP/BG	0.989 (0.984-0.995)	< 0.001	0.991 (0.985-0.996)	0.001	0.99 (0.984-0.997)	0.002
CP/BG ratio	0.987 (0.932-1.046)	0.664	0.989 (0.929-1.053)	0.723	0.991 (0.941-1.044)	0.736

BG: Blood glucose; CP: C-peptide; FCP: Fasting C-peptide; Model 1: Unadjusted; Model 2: Adjusted for duration, creatinine and alanine transaminase; Model 3: Adjusted for model 2 plus hemoglobin A1c; OR: Odds ratio; 2hCP: 2 hours postprandial C-peptide.

Table 4 Logistic regression of diabetic peri-neuropathy

	Model 1		Model 2		Model 3
	OR (95%CI)	P value	OR (95%CI)	P value	OR (95%CI)	P value
FCP	0.999 (0.998-1)	0.008	0.999 (0.998-1)	0.239	1 (0.999-1.001)	0.421
2hCP	1 (0.999-1)	0.001	1 (0.999-1)	0.008	1 (0.999-1)	0.046
Delta CP	0.999 (0.999-1)	0.003	0.999 (0.999-1)	0.007	1 (0.999-1)	0.042
CP ratio	0.994 (0.984-1.005)	0.294	0.994 (0.981-1.006)	0.324	0.994 (0.982-1.007)	0.372
FCP/fasting plasma glucose	0.989 (0.984-0.995)	0	0.992 (0.986-0.998)	0.009	0.993 (0.986-1)	0.042
2hCP/postprandial blood glucose	0.995 (0.992-0.998)	0.001	0.996 (0.993-0.999)	0.01	0.996 (0.993-1)	0.067
Delta CP/BG	0.996 (0.991-1)	0.035	0.996 (0.992-1)	0.077	0.997 (0.992-1.002)	0.298
CP/BG ratio	0.984 (0.948-1.022)	0.404	0.982 (0.932-1.036)	0.508	0.985 (0.943-1.029)	0.494

BG: Blood glucose; CP: C-peptide; FCP: Fasting C-peptide; Model 1: Unadjusted; Model 2: Adjusted for age, duration and alanine transaminase; Model 3: Adjusted for model 2 plus hemoglobin A1c; OR: Odds ratio; 2hCP: 2 hours postprandial C-peptide.

Table 5 Logistic regression of diabetic kidney disease

	Model 1		Model 2		Model 3
	OR (95%CI)	P value	OR (95%CI)	P value	OR (95%CI)	P value
FCP	1 (0.999-1.001)	0.805	0.999 (0.998-1)	0.121	0.999 (0.998-1)	0.267
2hCP	1 (1-1)	0.191	1 (0.999-1)	0.082	1 (0.999-1)	0.424
Delta CP	1 (0.999-1)	0.139	1 (0.999-1)	0.137	1 (0.999-1)	0.614
CP ratio	0.998 (0.987-1.009)	0.718	0.999 (0.989-1.009)	0.851	1 (0.99-1.01)	0.957
FCP/fasting plasma glucose	0.997 (0.991-1.003)	0.274	0.993 (0.986-1)	0.052	0.996 (0.988-1.003)	0.239
2hCP/postprandial blood glucose	0.997 (0.994-1)	0.05	0.996 (0.993-1)	0.033	0.998 (0.994-1.002)	0.264
Delta CP/BG	0.995 (0.991-1)	0.045	0.996 (0.991-1.001)	0.09	0.998 (0.993-1.003)	0.444
CP/BG ratio	0.977 (0.872-1.095)	0.687	0.99 (0.948-1.033)	0.635	0.992 (0.958-1.028)	0.67

BG: Blood glucose; CP: C-peptide; FCP: Fasting C-peptide; Model 1: Unadjusted; Model 2: Adjusted for duration, triglyceride, high-density lipoprotein cholesterol, creatinine and uric acid; Model 3: Adjusted for model 2 plus hemoglobin A1c; OR: Odds ratio; 2hCP: 2 hours postprandial C-peptide.