Association Between Hemoglobin Levels and Diabetic Foot Ulcer in Patients With Type 2 Diabetes: A Cross-Sectional Study

Background. Anemia is prevalent among patients with T2DM with DFU. However, there is limited research on the relationship between Hb level and DFU. Objective. To investigate the characteristics and relationship between Hb level and prognosis in patients with DFU. Materials and Methods. A total of 212 patients with T2DM were included and grouped according to the presence (n = 105) or absence (n = 107) of DFU. The independent t test and multiple logistic regression analysis were used to analyze the effect of different factors on the occurrence of anemia in patients with DFU and whether Hb level could be used to predict prognosis. Results. There were significant differences in clinical indicators that directly or indirectly contributed to anemia in patients with DFU (P < .05). Hb level was independently associated with DFU (OR, 0.899; P < .05). Hb levels were significantly decreased in patients aged 65 years or older (P < .05). Mild anemia was prevalent among most patients with DFU (59.62%). Hb level decreased with the severity of foot ulcer (P < .05) and was correlated with the duration of diabetes (R2 = 0.653; P < .05). The AUC value was 0.82, with a cutoff value of 122.5 g/L to identify patients with DFU at high risk of adverse outcomes. Conclusion. Anemia is common in patients with DFU. Anemia is a marker of DFU severity, and Hb level can predict poor prognosis in patients with DFU.

Abbreviations

ALB, albumin; AUC, area under the ROC curve; BMI, body mass index; Cr, creatinine; CVD, cardiovascular disease; DFU, diabetic foot ulcer; DN, diabetic neuropathy; DPN, diabetic peripheral neuropathy; ESR, erythrocyte sedimentation rate; FBG, fasting blood glucose; FIB, fibrinogen; Hb, hemoglobin; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; MCH, mean corpuscular Hb; MCV, mean corpuscular volume; OR, odds ratio; PAD, peripheral artery disease; PLT, platelet; RDW, red blood cell distribution width; ROC, receiver operating characteristic; SD, standard deviation; SUN, serum urea nitrogen; T2DM, type 2 diabetes; TG, triglyceride; WBC, white blood cell.

Introduction

DFUs are severe complications of T2DM characterized by deep tissue lesions related to neurological and PAD in the lower extremities.¹ The pathogenesis of DFU is multifaceted and involves both microscopic and macrovascular changes. Recent research has identified blood glucose control, peripheral neuropathy, and PAD as common risk factors for DFU.² The breakdown of foot tissue components resulting from the combination of these factors forms the basis for the development of foot lesions.³

The global prevalence of DFU is 6.3%, with a rate of approximately 4.1% in China.⁴ The lifetime incidence of DFU is estimated to be approximately 15% to 20%.⁵ Despite a significant reduction in severe amputations in China in recent years, successful treatment of DFU remains challenging. Even when ulcers heal, the recurrence rate after 1 year reaches 30% to 40%.⁶ A recent study reported a 5-year survival rate of 29% for patients with DFU, highlighting a stronger correlation between mortality and DFU compared with macrovascular lesions caused by other diseases.⁷ Bacterial infections and amputations associated with DFU have a detrimental effect on health-related quality of life, particularly in terms of mobility.^8,9 Additionally, individuals with DFU experience more frequent hospitalizations, longer hospital stays, increased emergency department visits, and higher household medical costs.^10,11

DFU poses a significant challenge to human health and socioeconomic aspects of society. These ulcers affect patients' quality of life and survival, and ultimately, increase the economic burden on individuals and countries. Despite advancements in the diagnosis and management of DFUs, their occurrence, recurrence, and expected outcomes have not improved significantly either in China or worldwide. Consequently, it is crucial to identify underlying factors that may slow the progression of DFU and improve patient survival rates and quality of life.

For anemia characterized by decreased Hb levels, the incidence of anemia was shown to be significantly higher in patients with diabetes with foot complications than in patients with diabetes without foot complications.¹² Anemia has a well-established prognostic effect in CVD and has been extensively studied and analyzed.¹³ However, anemia occurring in patients with diabetes has not received adequate attention, with reported incidence rates ranging from 20% to 45% different ethnic populations worldwide.¹⁴ The causes of anemia in patients with T2DM with DFU include chronic inflammatory anemia, diabetic nephrotic anemia, blood loss from wounds, and malnutrition. Chronic inflammation is considered a common cause of anemia in patients with diabetes, particularly in patients with DFU.^15,16 Studies suggest that certain pro-inflammatory cytokines can suppress the hematopoietic system and reduce serum iron levels, resulting in inadequate hematopoietic raw materials.¹⁷ Additionally, some diabetes medications have side effects that contribute to anemia. For instance, prolonged treatment with metformin can lead to vitamin B12 deficiency, characterized by anemia and peripheral neuropathy.¹⁸ Thiazolidinediones affect the kidneys and can cause fluid retention, leading to dilutional reduction of Hb levels.¹⁹

Anemia is associated with DFU, and management of DFU up to and including amputation may improve anemia. Although a 2021 study by Yammine et al²⁰ demonstrated an association between anemia and mortality in patients with DFU, the incidence, characteristics, and prognosis of anemia in patients with DFU have not been thoroughly investigated. Thus, the current study aimed to analyze the features of anemia in patients with DFU and assess the relationship between anemia and DFU prognosis. Such analysis is valuable in evaluating adverse outcomes in patients with DFU based on the initial Hb range or severity of anemia.

Materials and Methods

Materials

This cross-sectional study included all consecutive patients with DFU treated at the authors' institution from January 2021 to December 2022, as well as randomly selected patients with T2DM without DFU treated at the same hospital in that period. A total of 212 patients were enrolled in the study, with 105 consecutive patients with DFU constituting the case group and 107 randomly selected patients with T2DM without DFU from the same hospitalization period forming the control group. DFU was defined as a full-thickness wound, skin necrosis, or gangrene below the ankle caused by peripheral neuropathy or PAD in patients with T2DM. DFU severity was graded using the Meggit-Wagner ulcer classification system (Table 1).²¹

Table 1

The inclusion criteria were as follows: patients with T2DM aged 18 years or older with DFU and with an HbA1c level greater than or equal to 6.5%. Patients with foot ulcers resulting from a motor vehicle accident or a malignant disease were excluded. Anemia was defined according to the World Health Organization criteria, that is, Hb level less than 13 g/dL in males and less than 12 g/dL in females.²²

Candidate factors

A total of 33 correlating variables were included in the study. Demographic information of study participants included sex, age, BMI, tobacco use, drinking habits, family history, metformin use, diabetes duration, CVD, hypertension, DN, DPN, and PAD. Additionally, MCV, RDW, WBC count, PLT count, and ESR, as well as FBG, HbA1c, Hb, MCH, FIB, ALB, C-peptide, ferritin, total protein, TG, total cholesterol, HDL-C, LDL-C, Cr, and SUN levels were collected from the clinical records.

Outcome

All patients were followed for a minimum of 6 months or until death. Generally, the outcomes of DFUs were classified as "healed," "unhealed," "amputation," or "death." The prognosis of patients with DFU was categorized as either "good" (healed) or "poor" (unhealed, amputation, or death).

Statistical analysis

The normality of continuous variables was assessed using the Kolmogorov-Smirnov test. For variables with abnormal distribution, median (IQR) was used, and log conversion was applied when necessary to achieve normality. The transformed data were analyzed using the F test, while nonparametric tests were used when normality was not achieved. Furthermore, to examine the independent effects of Hb level on DFU, multifactor logistic regression analysis of Hb level and other significant difference factors was used. The associations were presented as OR with corresponding 95% CI and P value. The ROC curve was used to assess the ability of Hb levels to predict the outcome of patients with DFU with anemia during the follow-up period. The statistical significance level was set at .05. All statistical analyses were conducted using SPSS version 26.0 (IBM Corporation).

Ethics

The current study protocol was approved by the Ethics Committee of Wuxi Ninth People's Hospital (LW2023007). Written informed consent was obtained from all patients.

Results

After screening, 105 patients with T2DM with DFU (mean age [SD], 66.45 [11.77] years; range, 32-89 years) were recruited to the observation group. Additionally, 107 patients with T2DM without DFU (mean age, 63.52 [12.54] years; range, 34-91 years) during the same period were recruited to the control group. Statistically significant differences were found in tobacco use, diabetes duration, PAD, Hb level, MCH level, RDW, WBC count, PLT count, and FIB, ALB, total cholesterol, TG, Cr, and SUN levels (P < .05). No significant differences were found in sex, age, BMI, drinking, family history, metformin use, CVD, hypertension, DN, DPN, FBG level, HbA1c level, MCV, or ESR, or in C-peptide, ferritin, total protein, HDL-C, or LDL-C levels (P > .05) (Table 2). To examine the independent association between Hb level and DFU, a multifactor logistic regression analysis was performed using Hb levels and other significant difference factors. The results demonstrated that Hb levels (OR, 0.899; 95% CI, 0.839-0.963; P < .05) were independently associated with DFU (Table 3).

Table 2

Table 3

Hb level in patients with DFU was further analyzed. No significant difference was observed between males and females (P = .598) (Figure 1A). However, Hb level was found to decrease with increasing age in patients with DFU (P < .05) (Figure 1B). Additionally, 62 patients with DFU (59.05%) had an Hb level less than or equal to 120 g/L. Of these, 22 patients had moderate anemia (20.95%; Hb level, 31-60 g/L) and 2 had severe anemia (1.90%; Hb level < 60 g/L). However, 19 patients (18.10%) had an Hb level greater than or equal to 121 g/L (Figure 1C). Regarding the severity of foot lesions, it was observed that as the foot ulcers in patients with DFU became more severe, Hb level decreased (Figure 1D, Table 1). Furthermore, reduced Hb levels in patients with DFU were associated with increased diabetes duration (R² = 0.653; P < .05) (Figure 1E).

Among the anthropometric measures considered in the current study, Hb level played a crucial role in predicting adverse outcome in patients with DFU. The ROC curve analysis revealed an AUC of 0.82 for the Hb level, with a threshold value showing a sensitivity of 68.5% (95% CI, 0.60-0.78) and a specificity of 74.5% (95% CI, 0.66-0.83) (Figure 2A). Based on different cutoff values, the Youden index indicated that an Hb level of 122.5 g/L could be used to identify patients with DFU who were likely to experience adverse outcomes (Figure 2B).

Discussion

In the current study, the incidence of anemia in patients with DFU was as high as 81.73%. Multiple factors directly or indirectly contribute to the development of anemia in patients with DFU were statistically significant, including chronic inflammation, diabetic nephropathy, malnutrition, and hypoglycemic medications.²³

Some pro-inflammatory cytokines released by chronic inflammatory response can inhibit the hematopoietic system and decrease serum iron levels, resulting in inadequate hematopoietic raw materials and consequent anemia.²⁴ In the current study, there were statistically significant differences in tobacco use, diabetes duration, PAD, WBC count, PLT count, and FIB level between the 2 groups. Cigarette smoke causes vasomotor dysfunction, inflammation, and alterations in blood lipids.²⁵ Smoking-induced inflammatory response is attributed to increased reactive oxygen species and oxidative stress, which impair blood vessels and the nervous system^.26,27 Moreover, smoking plays a major role in PAD development by promoting atherosclerotic plaque formation.²⁸ PAD is an independent risk factor for amputation in patients with diabetes, and its prevalence increases with diabetes duration.^29,30 Higher WBC counts (>12 × 10⁹/L) indicate an inflammatory state and an increased risk of amputation.³¹ PLT activation induces an inflammatory response in the development of atherosclerosis in patients with diabetes, attracting more PLTs and WBCs to the site of inflammation.³² FIB is an acute inflammatory protein that can be used as a risk factor for DFU, and increased FIB levels are associated with acute foot ulcers and disease severity.³³ These inflammatory reactions may contribute somewhat to anemia in patients with DFU.

Hanna et al³⁴ demonstrated that diabetes-related chronic kidney disease leads to earlier and more severe anemia compared with non-diabetic chronic kidney disease. In the current study, elevated levels of CR and SUN suggest that kidney lesions are highly likely to cause anemia in patients with DFU.

In the current study, prolonged hyperglycemia and the chronic inflammatory state in DFU disrupted nutrient metabolism, resulting in decreased Hb and ALB levels, as well as increased TC and TG levels. Reduced Hb levels in patients with DFU can exacerbate ischemia and hypoxia at the ulcer site and hinder wound healing. Low ALB levels indicate poor nutritional status and potentially renal insufficiency, correlating with poor wound healing and chronic blood loss. Hypoalbuminemia is a well-established predictor of poor prognosis in patients with DFU.^35,36

Long-term metformin use can lead to vitamin B12 deficiency, a well-established side effect. The typical clinical manifestations of vitamin B12 deficiency are megaloblastic anemia and peripheral neuropathy.³⁷ In the current study, Hb and MCH levels were decreased, whereas MCV and RDW values were increased in patients with DFU. The incidence of anemia in patients with DFU reached 81.73%; lower Hb levels impede tissue perfusion and exacerbate lower extremity ischemia. Anemia also predisposes patients to thrombosis and hampers erythrocyte deformability, further worsening ischemia and delaying wound healing.^38,39 Treatment of DFUs up to and including amputation may improve anemia, promote healing, and improve survival.

The aforementioned factors collectively contribute to the frequent occurrence of anemia in patients with DFU. Therefore, investigating the association between Hb levels and DFUs holds significant value. The multivariate logistic regression analysis in this study revealed that Hb levels were the most significantly associated variable with DFUs. Iacopi et al⁴⁰ demonstrated an increased risk of anemia in male compared with female patients with DFU by analyzing Hb levels. In the current study, sex differences in Hb levels were not observed, potentially due to similar lifestyle factors among the selected groups. Elderly patients exhibited significantly decreased Hb levels, likely stemming from mobility difficulties, inappropriate diet, reduced protein intake, and impaired digestion and absorption, which may ultimately lead to malnutrition and subsequent anemia. The authors of the current study found a correlation between reduction in Hb levels and severity of DFUs, as well as a correlation between decreased Hb levels and diabetes duration.

Patients with T2DM and chronic poor blood glucose control are susceptible to various complications. HbA1c serves as an indicator of blood sugar control over a period of 2 to 3 months. An important consideration in patients with anemia as well as T2DM and DFU is the relationship between lower HbA1c levels and the possibility of undertreatment given a false sense of security on the part of the physician and patient. If a patient's level is not very high—indeed, Table 2 demonstrates slightly higher (although not significantly) HbA1c in the case group—it may lead to less strict blood sugar control, resulting in complications.⁴¹ HbA1c is the glycation product of Hb in red blood cells, formed through a slow, persistent, and irreversible process involving glucose in the blood.⁴² Additionally, in the current study HbA1c levels were not significantly elevated in patients with DFU, possibly due to reduced Hb levels leading to a decrease in non-enzymatic glycosylation substrates associated with blood sugar. The current study provides valuable supplementary information for clinicians when routine blood sugar control indicators in patients with DFU do not display significant abnormalities; this information is of value in facilitating early intervention.

These findings suggest a potential link between anemia and DFU, although the results of this study do not imply that anemia is a causative factor. Adeleye et al⁴³ previously demonstrated an association between anemia and mortality in patients with T2DM with DFU. Further investigation is required to determine the underlying mechanism of anemia caused by DFUs.

In the current study, ROC curve analysis demonstrated the potential of Hb level as a biomarker for predicting DFU prognosis, with an AUC of 0.82 and a cutoff value of 122.5 g/L for possible adverse outcomes. Hb measurement is a routine practice in routine bloodwork, and it holds promise as a practical prognostic indicator in patients with DFU.

Limitations

This study has certain limitations. First, the data were obtained from patients admitted to a single hospital, thus limiting generalizability. Further large-scale studies involving multiple hospitals are necessary to confirm these findings. Second, the available data did not provide insight into the specific causes of anemia and their correlation with primary outcomes in patients with DFU. Third, the retrospective nature of the study prevents establishment of a causal relationship between anemia and adverse outcomes.

Conclusion

The current study revealed a significant association between Hb levels and DFUs. Hb levels were notably lower in patients with T2DM and DFU than in patients with T2DM without DFU. Additionally, a positive correlation was observed between the severity of anemia and the severity of DFUs, and Hb levels were markers of the severity of DFUs. The study found that Hb level holds promise as a potential indicator of adverse outcomes in patients with DFU.

Acknowledgments

Authors: Fengying Jiang, MS; Qingyang Liu, PhD; and Qiubo Wang, PhD

Acknowledgments: The authors thank all the included patients for their valuable contribution to the study, and all the physicians, nurses, and technicians involved for their help.

Affiliation: Department of Clinical Laboratory, Wuxi Ninth People’s Hospital Affiliated to Soochow University, Jiangsu, China

ORCID: Wang, 0000-0002-4974-791X

Disclosure: This work was supported by grants from the scientific research project of Wuxi Science and Technology Bureau (Y20212054). The authors disclose no financial or other conflicts of interest.

Correspondence: Qiubo Wang, PhD; Department of Clinical Laboratory, Wuxi Ninth People’s Hospital Affiliated to Soochow University, No. 999 Liang Xi Road, Bin hu District Wuxi 214000, Jiangsu, China; wangqiubo2020@suda.edu.cn

Manuscript Accepted: January 17, 2024

How Do I Cite This?

Jiang F, Wang Q, Liu Q. Association between hemoglobin levels and diabetic foot ulcer in patients with type 2 diabetes: a cross-sectional study. Wounds. 2024;36(3):73-79. doi:10.25270/wnds/23109

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