Correlation between the Variability of Glycosylated Hemoglobin and Cardiovascular Risk in New-Onset T2DM Patients.

Objective: To investigate the relationship between glycosylated hemoglobin variant index and cardiovascular disease in patients with type 2 diabetes.
Methods: A total of 120 patients with type 2 diabetes who were admitted to the Department of Endocrinology in Chun'an Branch of Zhejiang Provincial People's Hospital from January 2014 to January 2017 were enrolled. The clinical data, fasting blood glucose, and glycosylated hemoglobin levels of the patients were collected, and HGI was obtained by calculating the FPG level into the formula. Follow-up for three years was performed to observe the cardiovascular disease (including coronary heart disease and ischemic stroke) in patients. The occurrence of CVD was analyzed in patients with different levels of HGI. Multivariate logistics regression analysis was used to analyze the risk factors of CVD in patients with T2DM.
Results: After three years of follow-up, 8 cases of 120 patients were lost to follow-up. In the end, 24 cases of CVD occurred in 112 patients, with an incidence rate of 21.43%. Comparing the clinical data of CVD patients and non-CVD patients, it was found that the proportion of age, FPG, HbA1c, HGI, and insulin control in the CVD group was higher than that of the non-CVD group, and the difference was statistically significant (P < 0.05). After grouping according to different HGI levels, it was found that with the increase of HGI level, the proportion of HbA1c, FPG, TC, CVD, and insulin use showed an upward trend (P < 0.05). Multivariate logistic regression analysis showed that high HGI level (OR = 4.660), older age (OR = 4.815), and higher FPG level (OR = 1.717) are independent risk factors that affect T2DM patients with cardiovascular disease (P < 0.05).
Conclusion: High HGI is independently associated with CVD events in patients with type 2 diabetes. HGI testing is helpful for clinical assessment of personalized assessment and prediction of cardiovascular risk in patients with diabetes.

1. Introduction

Diabetes (DM) is a public health problem attracting worldwide attention. According to the survey [1], in 2017, there were about 425 million adult diabetes patients in the world. China accounted for about 30% in the world, of which type 2 diabetes accounted for 90%. Diabetes can be complicated by multiple diseases which increase the patient's risk of death. HbA1c level can reflect the changes of blood glucose in patients in the past 8–12 weeks and is recommended as an important indicator of blood glucose control in patients with DM in clinical practice. Studies have shown [2] that HbA1c levels are highly associated with the risk of DM-related complications and cardiovascular disease. Active normalization of glycemic control reduces the risk of cardiovascular events and diabetes-related complications [3]. However, with the deepening of clinical studies, it has been found that HbA1c levels vary among different individuals. This difference is influenced by a variety of factors, such as blood glucose concentration, genetics, and red blood cell life cycle. Therefore, solely relying on HbA1c level to evaluate the risk of DM complicated with cardiovascular disease and related complications is not suitable for all populations, which will produce a significant deviation [4]. To this end, researchers developed a formula based on fasting blood glucose (FPG) to measure the difference between actual HbA1c and predicted HbA1c, which is called the HbA1c glycation index (HGI). At present, in foreign studies, this method has shown [5, 6] that observing HGI can predict the risk of DM microvascular and macrovascular complications well. However, studies on the efficacy of this method in Chinese people are not comprehensive. Therefore, the author's team conducted a follow-up study, and the report is as follows.

2. Data and Methods

2.1. Inclusion and Exclusion Criteria

Inclusion criteria are as follows: (1) the patient is in line with the diagnostic criteria for type 2 diabetes in China's guideline for prevention and treatment of type 2 diabetes (2010 edition) [7], (2) 18–70 years old, and (3) complete clinical data and persistent follow-up. Exclusion criteria are as follows: (1) patients with a history of coronary heart disease and stroke, (2) patients combined with malignant tumor or diseases of the blood system, and (3) patients taking medications such as glucocorticoid and acetylsalicylic acid that could affect the results of HbA1c tests. This study was a prospective follow-up study, in which a total of 120 patients with type 2 diabetes who were admitted to The Department of Endocrinology, Chun'an Branch of Zhejiang Provincial People's Hospital, from January 2014 to January 2017, were included.

2.2. Clinical Data Collection

Main information is as follows: (1) demographic characteristics: gender, age, body mass index (BMI), drinking history, smoking history, history of underlying diseases (hypertension, hyperlipidemia), etc., (2) laboratory indicators: it uses Beckman AU680 automatic biochemical analyzer to measure fasting blood glucose (FPG), total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL-C), high-density lipoprotein (HDL-C), and serum uric acid (SUA). It uses ion-exchange high-performance liquid chromatography to determine the level of HbA1c. The above biochemical indicators were measured every three months during follow-up until the occurrence of coronary heart disease/stroke or the end of follow-up, and the final results were averaged for statistical calculation.

2.3. Follow-Up

All patients were followed up every three months for three years and the last follow-up time was in January 2020. This study recorded the occurrence of coronary heart disease and ischemic stroke in all patients. The diagnosis of coronary heart disease conforms to the diagnostic criteria in the 2013 European Society of Cardiology Guidelines for Stable Coronary Heart Disease and Cardiovascular Disease with Diabetes [8] and the diagnosis of ischemic stroke conforms to the diagnostic criteria in the Chinese Guidelines for the Diagnosis and Treatment of Acute Ischemic Stroke 2014 [9].

2.4. HGI Calculation

Regression analysis was performed according to HbA1c and FPG. The regression equation predicted HbA1c = 4.79 + 0.306 × FPG and HGI = measured HbA1c − predicted HbA1c [10].

2.5. Statistical Method

This study uses the SPSS19.0 software for data analysis. Measurement data were expressed as mean ± standard deviation. Comparison between groups was performed by the t-test. Comparison between the three groups was performed by one-way ANOVA; case/percentage standard for counting data. The chi-square test was used for comparison between groups. The logistic regression equation was used for multivariate analysis. Pearson linear equation was used to analyze the correlation between HbA1c and FPG. The difference was statistically significant when P < 0.05.

3. Results

3.1. Follow-Up Results

By the last follow-up time, 8 of the 120 patients were lost to follow-up, and a total of 24 cases of CVD occurred in 112 patients, with an incidence of 21.43%. According to this, they were divided into the CVD group (n = 24) and the non-CVD group (n = 88).

3.2. HGI Level Results

The mean value of HbA1c in 112 patients of this study was (7.58 ± 1.15) %, and the mean value of FPG was (8.45 ± 2.71) mmol/L, and Pearson linear correlation analysis showed that HbA1c and FPG levels were positively correlated (r = 0.711, P < 0.001). Through regression analysis, the regression equation is predicted, HbA1c = 4.79 + 0.306 × FPG (see Figure 1), and HGI = measured HbA1c − predicted HbA1c. According to the calculated HGI values, the study subjects were divided into three groups by using the trine method: low HGI group (n = 37), medium HGI group (n = 38), and high HGI group (n = 37).

Figure 1

Correlation between HbA1c and FPG.

3.3. Comparison of Clinical Data between the CVD Group and Non-CVD Group

The proportion of age, FPG, HbA1c, HGI, and blood glucose control using insulin in the CVD group was higher than that in the non-CVD group. The difference was statistically significant (P < 0.05), as shown in Table 1.

Table 1

Comparison of clinical data between the CVD group and non-CVD group.

Clinical data	CVD group (n = 24)	Non-CVD group (n = 88)	t/χ2	P value
Gender			0.027	0.869
Male	13	46
Female	11	42
Average age (years)	67.13 ± 11.28	58.35 ± 10.94	3.462	0.001
BMI (kg/m2)	22.90 ± 3.17	22.85 ± 3.52	0.063	0.949
Drinking history n (%)	8	28	0.019	0.888
Smoking history n (%)	6	21	0.013	0.908
Hypertension n (%)	11	39	0.018	0.895
Hyperlipidemia n (%)	5	14	0.069	0.793
Drug treatment n (%)			6.793	0.009
Diabetes	11	65
Insulin	13	23
Laboratory index
FPG (mmol/L)	9.40 ± 1.58	7.22 ± 1.46	6.371	0
TC (mmol/L)	5.27 ± 1.28	5.24 ± 1.19	0.108	0.914
TG (mmol/L)	2.11 ± 0.53	2.09 ± 0.48	0.177	0.859
LDL-C (mmol/L)	3.23 ± 0.97	3.16 ± 0.85	0.347	0.729
HDL-C (mmol/L)	1.26 ± 0.23	1.28 ± 0.30	0.303	0.763
SUA (μmol/L)	371.45 ± 108.64	367.24 ± 112.56	0.164	0.87
HbA1c (%)	9.12 ± 1.29	8.11 ± 1.34	3.298	0.001
HGI level n (%)			30.065	0
Low HGI	1	36
Medium HGI	4	34
High HGI	19	18

3.4. Comparison of Clinical Data of Patients with Different HGI Levels

After grouping according to different HGI levels, the proportion of HbA1c, FPG, triglyceride (TC), CVD, and insulin use showed an increasing trend with the increase of HGI level (P < 0.05), as shown in Table 2.

Table 2

Comparison of clinical data of patients with different HGI levels.

Clinical data	Low HGI (n = 37)	Medium HGI (n = 38)	High HGI (n = 37)	F/χ2	P value
Gender				0.488	0.784
Male	21	20	18
Female	16	18	19
Average age (years)	60.24 ± 10.91	61.35 ± 11.23	60.78 ± 9.57	0.103	0.902
BMI (kg/m2)	22.89 ± 2.11	23.12 ± 2.85	22.56 ± 2.63	0.455	0.635
Drinking history n (%)	11	13	12	0.175	0.916
Smoking history n (%)	10	9	8	0.301	0.86
Hypertension n (%)	13	18	19	2.141	0.343
Hyperlipidemia n (%)	5	7	7	0.47	0.79
Drug treatment n (%)				13.039	0.001
Diabetes	31	28	17
Insulin	6	10	20
Laboratory index
FPG (mmol/L)	7.12 ± 1.31	8.23 ± 1.47	9.55 ± 1.29	29.601	0
TC (mmol/L)	5.12 ± 0.98	5.43 ± 1.02	5.98 ± 1.14	6.386	0.002
TG (mmol/L)	2.09 ± 0.36	2.10 ± 0.28	2.14 ± 0.43	0.199	0.82
LDL-C (mmol/L)	3.18 ± 0.76	3.22 ± 0.81	3.25 ± 0.79	0.074	0.929
HDL-C (mmol/L)	1.31 ± 0.32	1.26 ± 0.29	1.27 ± 0.30	0.283	0.754
SUA (μmol/L)	366.37 ± 121.45	370.18 ± 109.74	375.23 ± 103.46	0.059	0.943
HbA1c (%)	6.41 ± 1.05	7.23 ± 1.23	9.40 ± 1.58	51.943	0
CVD n (%)	1	4	19	30.065	0

3.5. Analysis of Multiple Factors Affecting CVD

Taking the occurrence of CVD as the dependent variable and age, insulin use, FPG, TC, HbA1c, and HGI levels as the dependent variables, the multivariate logistic regression analysis showed that higher HGI level (OR = 4.660), older age (OR = 4.815), and higher FPG levels (OR = 1.717) were independent risk factors for cardiovascular disease in T2DM patients (P < 0.05), as shown in Table 3.

Table 3

Logistic regression analysis of CVD risk.

Relevant indicators	β	S.E.	Wald	P value	OR	95% CI
						Lower limit	Upper limit
HGI level n (%)
Low HGI	1.345	0.71	3.59	0.058	3.839	0.955	15.434
Medium HGI	1.179	0.705	2.792	0.095	3.25	0.816	12.95
High HGI	1.539	0.642	5.742	0.017	4.66	1.323	16.406
Gender	1.572	0.633	6.17	0.013	4.815	1.393	16.64
FPG	0.541	0.224	5.818	0.016	1.717	1.107	2.664
HbA1c	0.702	0.641	1.202	0.273	2.019	0.575	7.087
TC	1.129	1.057	1.142	0.285	3.093	0.39	24.529
Insulin using	0.927	0.602	2.367	0.124	2.526	0.776	8.225

4. Discussions

Type 2 diabetes is a serious threat to human health. Studies on the effects of changes in related indicators of T2DM patients on complications and other diseases have been continuous. Studies have shown that glycemic control in patients with diabetes can significantly affect the risk and prognosis of complications. Indicators for assessing blood glucose control include FPG and HbA1c. Among them, HbA1c can reflect patients' blood glucose control within 8–12 weeks, which is more significant for assessing patients' risk of complications and prognosis. Studies in recent years [11, 12] have shown that HbA1c levels vary greatly among individuals, and some patients may have high or low HbA1c levels inconsistent with blood glucose control levels, which brings some difficulties to clinical prognosis assessment based on this indicator. In addition, current studies have shown [13] that patients with diabetes have a significantly increased risk of cardiovascular disease. Since cardiovascular disease is not a complication of diabetes, there is a lack of understanding and pertinence of indicators for assessing the risk of cardiovascular disease in patients with diabetes. HbA1c variation index (HGI) as a newly proposed index to measure the depth of HbA1c in recent years has been reported to be independently correlated with microvascular and macrovascular complications of diabetes mellitus [14, 15], but the research in the domestic population is not comprehensive. This direction has also gradually become a hot issue in the industry.

In this study, 112 patients with newly diagnosed type 2 diabetes mellitus were followed up for 3 years. The results showed that the age, FPG, HbA1c, HGI, and the proportion of blood glucose control in the CVD group were higher than those in the non-CVD group. Most CVD prevention strategies are aimed at middle-aged and elderly patients over the age of 40, and the age group over the age of 40 is regarded as an independent risk factor for CVD [16]. Fasting blood glucose is one of the important indicators of glycemic control in diabetic patients. Long-term hyperglycemia is an independent risk factor for cardiovascular disease in diabetic patients. Cardiovascular events are one of the main causes of death in diabetic patients [17]. Glycosylated hemoglobin (HbA1c) is a product of the covalent binding of glucose and hemoglobin, which is often used to reflect the glycometabolism function [18]. Studies have shown that [19] HbA1c levels are closely related to many chronic diseases, including hypertension and coronary heart disease, and can be used to predict the incidence rate of various cardiovascular and cerebrovascular diseases. Hempe et al. [5] analyzed the data from the famous American Diabetes cardiovascular disease risk study and found that the incidence of cardiovascular complications was higher in the high-HGI group compared with the low-HGI group. Van Steen et al. [20] analyzed the data of a large-scale study on the outcome of rrAR agonists (AleCardio) and found that the adverse cardiovascular events and all-cause mortality in the low HGI group were significantly lower than those in the high HGI group. With the increase of the HGI level, cardiovascular and cerebrovascular mortality increased significantly. Kim et al. [15] found that high HGI levels can increase the risk of cardiovascular events through a 10-year follow-up of T2DM patients. Cheng et al. [21] found that the risk of coronary heart disease in T2DM patients in the high HGI group was 2.9 times higher than that in the low HGI group. The higher the proportion of insulin used in diabetics, the longer the duration of the disease. The longer the blood vessel is affected by hyperglycemia, the more serious the damage is, which increases the risk of cardiovascular disease. Cumulative cardiovascular disease may occur.

At the same time, we differentiated the differences of related indicators of diabetes patients with different HGI levels, and the results showed that with the increase of HGI levels, the proportion of HbA1c, FPG, triglyceride (TC), CVD, and insulin use showed an increasing trend. Further multifactorial analysis of the risk of CVD in patients with new-onset type 2 diabetes showed that higher HGI levels (OR = 4.660), older age (OR = 4.815), and higher FPG levels (OR = 1.717) were independent risk factors for cardiovascular disease in T2DM patients; it is further confirmed that the greater the HbA1c variability in diabetic patients, the higher the risk of cardiovascular disease later. A follow-up study of 1248 newly diagnosed diabetes patients in foreign countries [22] showed that patients with high HGI also had increased cardiovascular morbidity and a 2.8 times increased risk of CVD compared with patients with abnormal glucose tolerance [23]. Another study [24] showed that HGI level was associated with carotid artery thickness in nondiabetic patients, suggesting that HGI can be used as a predictor of cardiovascular risk. This study also further confirms this point. In addition, another study [25] showed that the risk of coronary heart disease increased 2.9 times in patients with low HGI compared with those with high HGI. According to the report on the risk of diabetic nephropathy [26], the risk of diabetic nephropathy in patients with high HGI levels is 3.6 times higher than that in patients with low HGI levels. All the abovementioned domestic and foreign studies have shown that HGI is highly correlated with the risk of cardiovascular disease in diabetic patients, which can be used as a new predictive indicator for dynamic monitoring.

HbA1c is one of the diagnostic criteria for diabetes, but the application of HbA1c also has its limitations. Studies have found that HbA1c level is not only affected by some diseases such as hemoglobinopathy, uremia, and hemochromatosis but also affected by biological differences among individuals, and this difference has nothing to do with fasting blood glucose level [27-29]. In order to quantify this difference, Hempe et al. [30] first proposed the concept of hemoglobin variation index (HGI) in 2002. This is a method to measure the difference between actual HbA1c and predicted HbA1c based on fasting plasma glucose (FPG). As for the mechanism of HGI's influence on cardiovascular disease, the author's team analyzed that the higher the HGI is, the more the fluctuation of HBA1c level is reflected, which can more accurately reflect patients' blood glucose control and blood glucose fluctuation in the past 8–12 weeks than the traditional HbA1c index. In addition, some studies [31] have shown that HGI level is significantly correlated with inflammatory markers produced by C-reactive protein and polymorphonuclear leukocytes in the body. These results indicate that diabetic patients with high HGI levels present a high inflammatory state in vivo, resulting in greater damage to vascular endothelial cells and a greater risk of coronary heart disease or ischemic stroke. In addition, in this study, a higher proportion of patients with high HGI levels used insulin to control blood sugar, but for new type 2 diabetes patients, once the patient uses insulin, which indicates that the use of other blood glucose control drugs has been unable to control blood glucose well, the hyperglycemic state in their bodies will affect the function of various systems in the body, resulting in more negative effects. In addition, high HGI levels may be related to high oxidative stress in the body [32]. Oxidative stress seems to explain the relationship between blood glucose variability and adverse prognosis, but it is unclear whether a high HGI level caused by low-level fluctuation of blood glucose will increase this adverse risk. At present, the specific mechanism between the increase of HGI and the increased risk of cardiovascular disease is not clear. Felipe et al. [33] found that HGI level was positively correlated with the level of skin glycation end products (AGEs) in diabetic patients. Park et al. [34] found an abnormal increase in AGEs and their receptors in skin biopsy of diabetic peripheral neuropathy. AGEs is an intermediate product in response to chronic hyperglycemia. It has been found that AGEs can affect the structure and function of coronary artery and cardiomyocytes by inducing oxidative stress, promoting inflammatory response, changing the physiological function of vascular wall cells, increasing coronary lipid accumulation, mediating the change of myocardial vascular structure and function, and promoting myocardial disease and myocardial fibrosis, so as to lead to cardiovascular disease.

This study established the relationship between FPG and HGI through the model of the baseline regression equation, which made the results more reliable. However, due to the small sample size of this study, differences between different ages and genders as well as differences in diet and lifestyle of patients and the final results may be biased to some extent. Later, we will demonstrate this conclusion by increasing the sample size and further controlling relevant factors.

5. Conclusion

In conclusion, high HGI is independently associated with CVD events in patients with type 2 diabetes, and HGI testing contributes to personalized assessment and prediction of cardiovascular risk in patients with diabetes.