Association of Monocyte Count to HDL Cholesterol Ratio with Diabetic Retinopathy - A Prospective Observational Study

Introduction

Diabetic retinopathy (DR) is recognized as a significant contributor to visual impairment and is a common complication of diabetes. It results from the damage of retinal blood vessels, including capillaries, venules, and arterioles, which occurs due to hyperglycemia for a prolonged duration. The prevalence of diabetic retinopathy is approximately 35% among individuals with diabetes, indicating that a substantial portion of this population is affected by the condition. Within this group, about 7% experience proliferative diabetic retinopathy, which is a more severe form that carries an increased risk of vision loss. These prevalence rates can fluctuate depending on various factors, such as the specific population being studied and the diagnostic methods utilized.

DR is primarily classified into two stages: non-proliferative and proliferative. In the non-proliferative stage, the developing lesions are localized within the retina. However, neovascularization occurs as the disease progresses to the proliferative stage, forming new, abnormal blood vessels. This process can cause significant complications, including damage to the optic nerve and macula, which are vital for vision. Furthermore, proliferative diabetic retinopathy can result in vitreous hemorrhage and retinal detachment, both of which can severely impair eyesight. Given the potential for serious complications, early diagnosis of diabetic retinopathy is crucial for effective management and prevention of vision loss. Currently, there are no established biomarkers specifically for DRP, making the diagnosis primarily reliant on routine eye examinations conducted with ophthalmoscopy.

Several recent studies have investigated various inflammatory markers in the context of chronic microvascular and macrovascular complications associated with diabetes. Some of these markers include mean platelet volume (MPV), the neutrophil-to-lymphocyte ratio (NLR), elevated red cell distribution width (RDW), and the platelet-to-lymphocyte ratio (PLR).^1-4 These indicators have been explored for their potential role in assessing the inflammatory processes underlying diabetic complications.

Monocytes are known to contribute significantly to inflammatory responses in the body. In contrast, high-density lipoprotein (HDL) cholesterol has been shown to play a protective role by counteracting inflammation and promoting anti-inflammatory pathways.⁵ In this context, the monocyte count-to-HDL cholesterol ratio (MHR) has emerged as an intriguing metric in recent diabetes research. This ratio is gaining attention as a possible indicator of inflammatory status, with some studies suggesting that it may reflect underlying inflammation more accurately than other traditional markers.^6,7

Specifically, low HDL levels combined with high monocyte counts indicate increased inflammation in the body, serving as indirect indicators of this process. Research has shown that MHR can yield valuable insights regarding inflammation, supporting its potential utility in various health assessments.^6,7

The current study aims to delve deeper into the diagnostic potential of MHR as an indicator of diabetic retinopathy, exploring whether this neglected metric can effectively identify the condition in patients with diabetes. By investigating MHR in this context, the study seeks to contribute to understanding inflam-mation’s role in diabetic retinopathy and enhance early diagnostic strategies for this serious complication.

Objectives of the study

1. To measure HDL cholesterol levels and Monocyte count in all patients.

2. To compare the relation of Monocyte to HDL cholesterol ratio among patients with proliferative diabetic retinopathy, nonproliferative diabetic retinopathy, and without diabetic retinopathy groups.

Materials and Methods

Study Design and Setting

This cross-sectional study was conducted at the Medicine Department of Gadag Institute of Medical Sciences, Gadag, from July 2023 to December 2023. The study population comprised patients with Type 2 diabetes mellitus who presented eye complaints to the outpatient and inpatient medicine departments during the study period.

Where:

• n = Sample size

• Z = Z-value for the desired confidence level (1.96 for 95% confidence)

• p = Prevalence13 - 16.9 % i.e., (0.169)

• E = Margin of error - 7%, i.e., (0.07)

The required sample size would be approximately 100 participants.

Selection Criteria

The study included patients above 18 years with HbA1c levels greater than 6.5% and a documented history of type 2 DM for at least 5 years. Patients were excluded if they had type 1 diabetes mellitus, acute inflammation or infection, history of smoking, acute or chronic renal failure, chronic liver or heart diseases, and microvascular complications of diabetes except diabetic retinopathy, uncontrolled hypertension, coronary artery disease, cerebrovascular disease, or connective tissue diseases. Additionally, patients with ocular diseases except diabetic retino-pathy, macular edema, previous retinal laser photocoagulation and intravitreal injection history, history of any surgery within the last 3 months, or those unwilling to provide informed consent were excluded.

Ethical Considerations

The study protocol was conducted per the ethical principles, and informed consent was obtained from all participants before their inclusion.

Data Collection and Assessment

Data collection was performed using a standardized proforma. Detailed medical history, physical exami-nation findings, and comprehensive ophthalmological examination were conducted for each patient. The clinical profile was documented along with a detailed diabetic history, including the duration of diabetes, current medication regimen, and HbA1c values. Routine blood investigations were performed, including HDL cholesterol levels, and all patients underwent fundoscopic examination.

Patient Classification

Based on ophthalmological evaluation, patients were categorized into three groups: proliferative diabetic retinopathy (PDR), nonproliferative diabetic retino-pathy (NPDR), and without diabetic retinopathy.

Statistical Analysis

Statistical analysis was performed using SPSS software version 22.0. Quantitative data was presented as mean ± standard deviation, while categorical data was expressed as frequencies. The Shapiro-Wilk test was used to determine the normality of distribution, and the Levene test assessed the homogeneity of distribution. One-way ANOVA was performed to compare groups, followed by post hoc analysis using Tukey's HSD test. Statistical significance was set at P < 0.05.

Results

The study population comprised 100 participants, with a gender distribution of 46 males (46%) and 54 females (54%). The overall mean age of the study population was 58.32 ± 12.13 years. Male participants had a mean age of 59.83 ± 11.15 years, while female participants had a mean age of 57.09 ± 13.37 years.

Age distribution analysis revealed that most partici-pants were in the 51-60 age group, accounting for 32% of the total population (16% males and 16% females). The second largest group was 61-70 years, comprising 24% of participants (10% males and 14% females). The 41-50 age group represented 18% of the population (10% males and 8% females), followed by the 71-80 years group with 15% (4% males and 11% females). Younger age groups of 21-30 years and 31-40 years collectively represented 8% of the population. A small percentage of participants (3%) were above 80 and were all male.

Regarding the duration of diabetes, the study found that among the 78 diabetic patients (excluding the 22 without diabetic retinopathy subjects who did not have diabetes), the mean duration was 8.86 ± 4.98 years. The majority of diabetic patients (43%) had been diagnosed between 6 and 10 years before the study. Twenty patients (20%) had diabetes for 11-15 years, while 12 patients (12%) had diabetes for 16-20 years. Only three patients (3%) had diabetes for more than 20 years.

The study population was categorized into three groups based on ophthalmological evaluation. The proliferative diabetic retinopathy group was the largest, with 43 patients, followed by the non-prolife-rative diabetic retinopathy group, with 35 patients. 22 participants were without diabetic retinopathy.

Statistical analysis of the Monocyte to HDL chole-sterol ratio (MHR) revealed significant differences between the diabetic retinopathy groups (proliferative and nonproliferative) when compared with the without diabetic retinopathy group (P = 0.046).

The without diabetic retinopathy group demonstrated the lowest MHR value (0.0113 ± 0.06), while the non-proliferative group showed the highest ratio (0.0145 ± 0.02), followed by the proliferative group (0.0125 ± 0.02). The age distribution across groups showed variation, with and without the diabetic retinopathy group having a mean age of 69.5 ± 10.3 years, while both the non-proliferative and proliferative groups had similar mean ages of 65.8 ± 10.6 years and 65.2 ± 8.9 years, respectively.

Statistical analysis of the Monocyte to HDL choles-terol ratio (MHR) revealed significant differences between the diabetic retinopathy groups (proliferative and nonproliferative) when compared with the without diabetic retinopathy group (P = 0.046) by using One-way ANOVA test. Post hoc analysis using Tukey’s HSD test showed a significant difference between the without diabetic retinopathy and proliferative retino-pathy groups (P = 0.040) but no significant difference between the without diabetic retinopathy and non-proliferative groups (P = 0.125).

Discussion

Diabetic individuals are at risk of developing both microvascular complications, such as retinopathy, neuropathy and nephropathy, as well as macrovascular complications, such as coronary artery disease. These complications stem from changes in blood viscosity, capillary structure, permeability, and platelet function, which are influenced by fluctuations in blood glucose and the duration of diabetes. Diabetic retinopathy (DR) is a major microvascular complication.

While monocytes play a role in promoting inflam-mation, HDL cholesterol helps reduce inflammation by activating anti-inflammatory pathways. The ratio of monocytes to HDL cholesterol (MHR) has been increasingly studied as a potential inflammatory marker in diabetes. Although other hematological indices, such as NLR, PLR, and MPV, have been examined, MHR has been less explored.

Previous studies have examined MHR in relation to both macrovascular and microvascular complications of diabetes. For instance, Kundi et al., found an association between MHR and SYNTAX scores in patients with coronary artery disease.⁸ Cetin et al., identified MHR as an independent indicator of coronary artery disease severity and the risk of future cardiovascular events.⁹ Karatas et al., suggested that higher MHR might be a marker for diabetic nephro-pathy.¹⁰ In contrast, Vural et al., found increased MHR values in patients with diabetic neuropathy, suggesting its potential use in diagnosing neuropathy.¹¹ However, Pençe et al., did not find a strong link between MHR and cardiovascular risk, specifically in diabetic neuropathy patients. However, the broader patient population observed a general correlation between MHR and cardiovascular risk. There is limited research on the relationship between MHR and diabetic retinopathy.¹²

In our study, we prospectively examined 100 patients with and without DR and found a significant difference between the groups. Post hoc analysis using Tukey’s HSD test showed an essential difference between the without diabetic retinopathy and proliferative retinopathy groups (P = 0.040) but no significant difference between the without diabetic retinopathy and non-proliferative groups (P = 0.125). Given that MHR values were not significantly different between the without diabetic retinopathy and non-proliferative groups and that HbA1c levels were similar in the proliferative and non-proliferative groups, it suggests that MHR is more influenced by the proliferative stage of the disease rather than by diabetes itself. This finding supports the potential of MHR as a marker for diabetic proliferative retinopathy. However, the study's small sample size is a limitation, and further research with larger patient populations is needed to explore the link between MHR and diabetic retinopathy more comprehensively.

Limitations of the study

Limited sample size: One of the main limitations of this study is the relatively small number of participants, which may affect the generalizability of the findings. Larger sample sizes are needed to confirm the results and ensure they accurately represent the broader diabetic population.

Focus on DR Only: This study exclusively investigated diabetic retinopathy without considering other microvascular (e.g., neuropathy and nephropathy) or macrovascular complications (e.g., coronary artery disease). Expanding the study to include these conditions could help determine whether MHR is specific to diabetic retinopathy or if it could serve as a broader marker of inflammation across all diabetic complications.

Conclusion

In conclusion, MHR shows promise as an inflam-matory marker for diabetic retinopathy, especially in proliferative forms. However, additional studies with larger sample sizes and longer follow-up durations are required to solidify the relationship between MHR and diabetic retinopathy.

Conflict of interest

None

Acknowledgement

The authors would like to thank all the Teaching and Non-Teaching Staff and postgraduate residents of Gadag Institute of Medical Sciences, Gadag, for their cooperation and support throughout the study and for timely help preparing charts and tables.