Serum Cystatin C in the Diagnosis of Early DN and Its Comparison with UACR: A Cross-sectional Observational Study

INTRODUCTION

American Diabetes Association (ADA; 2014) defines diabetes mellitus (DM) as a collection of metabolic disorders characterized by elevated blood glucose levels due to abnormalities in insulin secretion, insulin action, or a combination of both.¹

Diabetes represents a major challenge for global healthcare systems, with its prevalence rising rapidly, particularly in developing countries like India. This increase is mainly due to growing rates of overweight/obesity and unhealthy lifestyles.²

Diabetes can lead to a variety of complications affecting different organs, which are typically divided into 2 main categories: Microvascular complications (including nephropathy, retinopathy, and neuropathy) and macrovascular complications (including cerebrovascular disease, peripheral vascular disease, and ischemic heart disease).³ Among these, nephropathy is a significant contributor to both disease burden and mortality.

Diabetic nephropathy (DN) is a chronic, progressive kidney disease linked to diabetes, caused by structural and functional alterations in the glomeruli and tubules due to impaired glucose regulation. In India, DN accounts for about 46% of chronic kidney diseases in the elderly. The occurrence of DN has significantly increased among diabetics, establishing it as the primary cause of end-stage renal disease (ESRD).⁴

The primary goal in managing diabetes is to identify an effective early marker for the detection of early-stage DN, preventing its progression to ESRD. Therefore, early identification of nephropathy in diabetic patients is crucial for timely intervention.

Several risk factors contribute to the onset and progression of DN. Some, like hypertension and hyperglycemia, can be managed through treatment. Others, such as smoking and dietary habits, can be modified through lifestyle changes. While genetic factors remain constant, altering epigenetic influences on gene expression could potentially reduce the risk of DN, even in individuals with a genetic predisposition.⁵

Thus, the study aimed to compare serum cystatin C and the urinary albumin-to-creatinine ratio (UACR) as biomarkers for the early detection of DN.

MATERIALS AND METHODS

This cross-sectional observational study was conducted at the Department of General Medicine, ESIC Medical College and Hospital, Faridabad, from 2021 to 2024, after receiving approval from the institutional ethics committee. Sample collection took place over a period of 1 year. The study included diabetic patients who met the criteria and provided written informed consent during the study period.

RESULTS

Table 1 illustrates that out of 50 patients, the majority (34 or 68%) were aged between 41 and 50 years, followed by 13 patients (26%) in the 31−40 years age-group, and 3 patients (6%) in the 21−30 years age-group. The mean age of the participants was 43.06 ± 6.9 years. Regarding gender, 52% of the participants were male and 48% were female. The most common symptoms reported were polyuria and fatigue, each affecting 56% of patients, followed by polydipsia in 38%, and weight loss in 34%. In terms of disease stage, 15 patients (30%) were classified as stage I (hyperfiltration), 11 patients (22%) as stage II (silent), and 24 patients (48%) as stage III (incipient nephropathy).

Table 2 shows diabetes parameters where mean values for FBS, PPBS, RBS, and HbA1c were 224.82 ± 79.02 mg/dL, 341 ± 90.1 mg/dL, 331.56 ± 76.98 mg/dL, and 9.85 ± 2.37%, respectively.

Table 3 presents the relationship between the duration of diabetes, smoking status, and serum cystatin C levels with the stages of DN. Among the patients, 31 (62%) had been diagnosed with diabetes for 0−5 years. Smoking was reported in 37 (74%) of the cases, and serum cystatin C levels were elevated in 39 (78%) of the patients. A significant association was observed between serum cystatin C levels and the stages of DN (p < 0.05), while no significant association was found between the duration of diabetes or smoking status and the stages of DN (p > 0.05).

Table 4 presents the differences in the duration of diabetes, smoking status, serum cystatin C levels, and UACR across the stages of DN. The average duration of diabetes was 4.4 ± 3.48 years. The mean serum cystatin C level was 1.19 ± 0.39 mg/L, while the average UACR was 95.22 ± 102.15 mg/gm, and the mean GFR was 102.62 ± 28.54 mL/min/1.73 m². Significant differences were observed in the mean duration of diabetes, serum cystatin C levels, GFR, and UACR across the stages of the Mogensen classification.

DISCUSSION

In our study, the largest proportion of patients (68%) fell within the 41−50 years age-group, followed by 26% in the 31−40 years age-group. This age distribution is similar to that observed in the study by Ashok et al., where 39% of patients fell into the 41−50 years category.⁷ The mean age in our study was 43.06 years, which is slightly lower than the mean age of 52.0 ± 11.0 years reported by Sapkota et al. in their study of Type 2 DM (T2DM) patients.⁸ Additionally, Chatterjee et al. found that the prevalence of T2DM increases with age, especially after 40, which aligns with the findings of our study.⁹ Regarding gender distribution, our study population consisted of 52% males and 48% females, which mirrors the slightly higher global prevalence of T2DM in males as observed by Kautzky-Willer et al.¹⁰ Other studies, however, have reported a higher proportion of males, such as 54 and 36.2%, respectively.^8,11 The most frequently reported symptoms in our study were polyuria and fatigue (both 56%), followed by polydipsia (38%) and weight loss (34%). These are consistent with findings from Chatterjee et al., who highlighted polyphagia, polydipsia, and polyuria as classic symptoms in T2DM patients with uncontrolled hyperglycemia.⁹

The majority of our patients (62%) had been diagnosed with diabetes for 0−5 years, similar to the median duration of 5 years reported by Sapkota S et al.⁸ However, Chatterjee et al. noted that the duration of diabetes can vary significantly among individuals, influenced by factors such as the age at diagnosis, lifestyle, and treatment adherence.⁹ Regarding smoking, 74% of our participants reported no history of smoking, while 26% were smokers. Studies by Willi et al. and Pan et al. found that smoking contributes to insulin resistance and impaired glucose metabolism, thereby increasing the risk of developing T2DM.^12,13

In our study, the mean GFR was 102.62 ± 28.54 mL/min/1.73 m², which falls within the normal range. However, the mean FBS was 224.82 ± 79.02 mg/dL, PPBS was 341 ± 90.1 mg/dL, RBS was 331.56 ± 76.98 mg/dL, and HbA1c was 9.85 ± 2.37%, all of which indicate poor glycemic control, aligning with the diagnostic criteria for DM (ADA, 2023).¹⁴

Our study observed that the mean duration of diabetes was 2.42 ± 2.37 years for stage I participants, 4.7 ± 3.74 years for stage II, and 6.08 ± 3.92 years for stage III, suggesting that the severity of DN increases with the duration of the disease.

We found elevated serum cystatin C levels in 78% of patients, with a mean level of 1.19 ± 0.39 mg/L. Increased serum cystatin C levels in DN patients have been previously reported by Jeon et al., Cho et al., Alicic et al., and Mussap et al., who observed this increase particularly in patients with T2DM and DN.^6,15−17 Serum cystatin C levels rise as GFR decreases, leading to its accumulation in the bloodstream.⁶

The mean UACR in our study was 95.22 ± 102.15 mg/gm, indicating a significant presence of microalbuminuria (ACR between 30 and 300 mg/gm) in many of our participants. Microalbuminuria is an early indicator of DN, and as DN progresses, overt proteinuria and a decline in estimated GFR (eGFR) typically follow. Studies by Cho et al. and Alicic et al. found DN in 20−40% of T2DM patients.^15,16

Our findings showed that 30% of patients were classified as stage I (hyperfiltration), 22% as stage II (silent), and 48% as stage III (incipient nephropathy). Patients in stage I exhibited higher mean GFR values than those in stage II, and those in stage II had higher GFR than patients in stage III. This progression of decreasing GFR is typical in DN, supporting its natural course.

Of the study subjects, 52% showed normoalbuminuria, while 48% had microalbuminuria. The mean UACR values were 10.3 in stage I, 17.7 in stage II, and 183.78 in stage III, highlighting the presence of microalbuminuria in the more advanced stages of DN.

We also observed a progressive increase in mean serum cystatin C levels with advancing stages of DN. Elevated cystatin C levels in normoalbuminuric patients in stages I and 2 emphasize its potential as an early diagnostic marker for DN, detectable even before the onset of microalbuminuria. Therefore, it offers an early detection tool, aiding in the implementation of preventative and treatment strategies to reduce the risk of developing ESRD. A similar study by Gupta et al. found elevated cystatin C levels in patients who had not yet developed microalbuminuria, supporting the potential of cystatin C as an earlier marker of DN.¹⁸

In this study, we found a moderately positive correlation (correlation coefficient 0.53) between serum cystatin C levels and UACR across all study participants. Moreover, there was a strong positive correlation (correlation coefficient 0.647) between serum cystatin C levels and UACR in stage III patients, indicating a stronger correlation as DN progresses. This finding is consistent with studies by Sapkota et al., Jeon et al., and Shohaib et al., who also observed a positive correlation between serum cystatin C and albuminuria in T2DM patients.^6,8,19 The correlation between serum cystatin C and UACR suggests that both biomarkers reflect the underlying pathophysiological process of renal dysfunction in T2DM patients.^6,19

CONCLUSION

The study emphasizes the promising role of cystatin C as a biomarker for early DN. Elevated levels of serum cystatin C were detected in stages I and II of DN, even before microalbuminuria sets in. This highlights its potential to detect DN at an earlier, more manageable stage, making cystatin C a key tool in proactive diagnosis and intervention. Its significant association with both the Mogensen classification and UACR further supports its clinical relevance. These findings suggest that combining serum cystatin C with other biomarkers could improve diagnostic accuracy in diabetic patients.

ORCID

Abhishek https://orcid.org/0009-0000-9077-6459

Anjali https://orcid.org/0009-0004-4453-6090

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