Diabetic nephropathy is a chronic renal complication of diabetes mellitus and represents a major contributor to chronic kidney disease and end-stage renal disease. It develops through a complex interaction of metabolic, haemodynamic, inflammatory and genetic mechanisms. Persistent hyperglycaemia promotes advanced glycation end-product formation, oxidative stress, endothelial dysfunction, mesangial expansion and thickening of the glomerular basement membrane. Over time, these changes progress to nodular glomerulosclerosis, tubulointerstitial fibrosis and vascular lesions.

HbA1c is a useful marker of long-term glycaemic exposure and reflects the average blood glucose concentration over the preceding two to three months. Higher HbA1c levels have been linked to microvascular injury in diabetes. In diabetic nephropathy, poor glycaemic control accelerates glomerular basement membrane thickening, mesangial matrix accumulation and podocyte injury. However, the severity of renal damage cannot always be predicted by HbA1c alone, because several patients with similar glycaemic control may show different degrees of pathological renal involvement.

Dyslipidaemia is another important metabolic disturbance in diabetes. Elevated triglycerides, increased LDL cholesterol, low HDL cholesterol and small dense LDL particles may contribute to endothelial injury and intrarenal lipid accumulation. Lipotoxicity can worsen mesangial cell dysfunction, tubular epithelial injury, macrophage recruitment and interstitial fibrosis. Thus, lipid abnormalities may act not only as cardiovascular risk factors but also as contributors to progressive renal injury.

Inflammation is increasingly recognised as a central component in the pathogenesis of diabetic nephropathy. Inflammatory mediators such as high-sensitivity C-reactive protein, interleukin-6 and tumour necrosis factor-alpha may reflect systemic and renal inflammatory activity. These markers are associated with endothelial dysfunction, increased vascular permeability, tubular injury and extracellular matrix deposition. Their relationship with renal histopathology is clinically relevant because inflammatory activation may identify patients with more aggressive renal disease.

Renal biopsy remains the most direct method for assessing pathological injury in diabetic nephropathy. It allows evaluation of glomerular lesions, interstitial fibrosis, tubular atrophy, interstitial inflammation and vascular changes. The Renal Pathology Society classification provides a structured approach for grading diabetic nephropathy, ranging from mild glomerular basement membrane thickening to advanced global glomerulosclerosis. The present study was conducted to evaluate the association of HbA1c, lipid profile and inflammatory markers with pathological changes in diabetic nephropathy.

Study Design This was a hospital-based observational analytical study conducted to assess the relationship between biochemical markers and renal pathological changes in patients with diabetic nephropathy. The study involved clinical evaluation, laboratory investigations and renal biopsy assessment. Patients were not exposed to any experimental intervention, and all investigations were performed as part of diagnostic evaluation and disease assessment. Place of Study The study was carried out at Kakatiya Medical College, Hanumakonda, with clinical and laboratory support from the departments involved in General Medicine, nephrology, biochemistry and pathology services. Study Duration The study was conducted over a period of 12 months, from November 2023 to October 2024. Study Population The study population included patients with diabetes mellitus who had clinical evidence of renal involvement and underwent renal biopsy. Patients with biopsy findings consistent with diabetic nephropathy were included in the final analysis. Both male and female patients were considered eligible if complete clinical, biochemical and histopathological data were available. Sample Size A total of 110 patients with biopsy-proven diabetic nephropathy were included in the study. Inclusion Criteria Patients aged 30 years and above with diabetes mellitus, evidence of diabetic kidney disease and renal biopsy findings consistent with diabetic nephropathy were included. Patients with available HbA1c, lipid profile, renal function tests, urine albumin-creatinine ratio and inflammatory marker results were considered for analysis. Exclusion Criteria Patients with biopsy-proven primary glomerulonephritis unrelated to diabetes, lupus nephritis, vasculitis, obstructive nephropathy, acute kidney injury due to non-diabetic causes, active systemic infection, malignancy, chronic liver disease or incomplete laboratory records were excluded. Patients receiving long-term immunosuppressive therapy were also excluded because such treatment could alter inflammatory marker levels. Clinical Assessment A detailed clinical history was recorded for each patient, including age, sex, duration of diabetes, treatment history, presence of hypertension, smoking status and family history of kidney disease. Blood pressure was measured using standard procedures. Body mass index was calculated using weight in kilograms divided by height in metres squared. Laboratory Investigations Venous blood samples were collected under aseptic precautions after overnight fasting. HbA1c was measured using standard laboratory methods. Fasting blood glucose, serum creatinine, blood urea, total cholesterol, triglycerides, LDL cholesterol, HDL cholesterol and VLDL cholesterol were estimated. Estimated glomerular filtration rate was calculated using a standard creatinine-based equation. Urine albumin-creatinine ratio was measured from a spot urine sample. Inflammatory markers included high-sensitivity C-reactive protein, interleukin-6 and tumour necrosis factor-alpha. These markers were assessed using validated laboratory methods according to manufacturer instructions and internal quality control procedures. Renal Biopsy Procedure and Histopathological Evaluation Renal biopsy was performed in clinically indicated cases after obtaining informed consent and ensuring adequate pre-biopsy evaluation. Tissue sections were processed for light microscopy using routine and special stains, including haematoxylin and eosin, periodic acid-Schiff, Masson’s trichrome and silver methenamine stains wherever required. Diabetic nephropathy was classified according to pathological class. Tubulointerstitial fibrosis, tubular atrophy, interstitial inflammation, arteriolar hyalinosis and arteriosclerosis were separately recorded. Pathological Classification Glomerular lesions were categorised as class IIa, class IIb, class III and class IV. Class IIa represented mild mesangial expansion, class IIb represented severe mesangial expansion, class III represented nodular sclerosis and class IV represented advanced diabetic glomerulosclerosis. Tubulointerstitial and vascular lesions were graded semi-quantitatively. Statistical Analysis Data were entered into a spreadsheet and analysed using statistical software. Continuous variables were expressed as mean ± standard deviation. Categorical variables were expressed as number and percentage. One-way ANOVA was used to compare continuous variables across pathological classes. Chi-square test was used to assess the association between categorical variables. Correlation analysis was performed to evaluate relationships between biochemical markers and pathological severity. A p-value of <0.05 was considered statistically significant. Ethical Considerations The study was conducted after institutional approval. Written informed consent was obtained before biopsy and use of clinical data. Patient confidentiality was maintained throughout the study. Data were anonymised before analysis, and no personal identifiers were used in the manuscript.

Baseline Characteristics of the Study Population

A total of 110 patients with biopsy-proven diabetic nephropathy were included in the study. The mean age was 56.8 ± 10.9 years. There were 68 males (61.8%) and 42 females (38.2%). The mean duration of diabetes was 10.7 ± 4.8 years. Hypertension was present in 76 patients (69.1%). The mean HbA1c was 8.4 ± 1.3%, indicating that a substantial proportion of patients had suboptimal glycaemic control. The mean urine albumin-creatinine ratio was 1,126 ± 890 mg/g, and the mean estimated glomerular filtration rate was 50.6 ± 21.4 mL/min/1.73 m² (Table 1).

Table 1: Baseline clinical and biochemical profile of the study population

Values are expressed as mean ± SD or n (%). BMI: body mass index; eGFR: estimated glomerular filtration rate; hs-CRP: high-sensitivity C-reactive protein; IL-6: interleukin-6; TNF-alpha: tumour necrosis factor-alpha.

Distribution of Pathological Classes

Based on renal biopsy findings, class IIa diabetic nephropathy was seen in 22 patients (20.0%), class IIb in 30 patients (27.3%), class III in 36 patients (32.7%) and class IV in 22 patients (20.0%). Nodular glomerulosclerosis was therefore observed in nearly one-third of the study group, while advanced diabetic glomerulosclerosis was present in one-fifth of patients. The distribution of pathological classes is shown in Table 2 and Figure 1.

Table 2: Distribution of diabetic nephropathy pathological classes

Pathological classes were based on glomerular lesions observed in renal biopsy specimens.

Figure 1: Distribution of pathological classes in diabetic nephropathy

Association of HbA1c with Pathological Severity

Mean HbA1c increased steadily with advancing pathological class. Patients with class IIa lesions had a mean HbA1c of 7.1 ± 0.8%, whereas patients with class IV lesions had a mean HbA1c of 9.4 ± 1.2%. This difference was statistically significant (F=26.51, p<0.001). Poor glycaemic control was also more frequent among patients with advanced lesions. Among patients with HbA1c ≥9.0%, 30 of 45 patients (66.7%) had class III or class IV disease, compared with 6 of 20 patients (30.0%) among those with HbA1c <7.0% (χ²=7.92, p=0.019) (Table 3; Figure 2).

Table 3: Association of HbA1c category with advanced pathological lesions

Data are expressed as n (%). Chi-square test was used. A p-value <0.05 was considered statistically significant.

                                           Figure 2: HbA1c categories and pathological severity

Lipid Profile Across Pathological Classes

A progressive worsening of lipid parameters was observed across pathological classes. Mean total cholesterol increased from 181 ± 31 mg/dL in class IIa to 232 ± 42 mg/dL in class IV. Mean triglycerides increased from 148 ± 46 mg/dL to 224 ± 68 mg/dL across the same categories. LDL cholesterol also showed a significant rise, while HDL cholesterol declined with increasing severity. These differences were statistically significant for total cholesterol (F=10.54, p<0.001), triglycerides (F=12.02, p<0.001), LDL cholesterol (F=9.81, p<0.001) and HDL cholesterol (F=13.75, p<0.001) (Table 4; Figure 3).

Table 4: Comparison of lipid profile and renal parameters across pathological classes

Values are expressed as mean ± SD. One-way ANOVA was used for comparison across pathological classes. ACR: albumin-creatinine ratio; eGFR: estimated glomerular filtration rate.

Figure 3: Progressive change in lipid parameters across pathological classes

Association of Dyslipidaemia with Advanced Pathological Lesions

Dyslipidaemia was present in 65 patients (59.1%). Among patients with dyslipidaemia, 40 patients (61.5%) had class III or class IV disease, compared with 18 patients (40.0%) among those without dyslipidaemia. This association was statistically significant (χ²=4.12, p=0.042). These findings suggest that an atherogenic lipid pattern may be linked with more severe renal structural injury in diabetic nephropathy (Table 5).

Table 5: Association of dyslipidaemia with advanced pathological lesions

Data are expressed as n (%). Chi-square test was applied. Dyslipidaemia was defined by abnormality in one or more lipid parameters according to laboratory reference cut-offs.

Inflammatory Markers and Pathological Severity

Inflammatory markers showed a strong relationship with pathological progression. Mean hs-CRP increased from 2.8 ± 1.1 mg/L in class IIa to 7.6 ± 3.1 mg/L in class IV. Mean IL-6 increased from 8.2 ± 3.0 pg/mL to 20.1 ± 7.4 pg/mL, while TNF-alpha increased from 16.1 ± 5.1 pg/mL to 31.8 ± 9.4 pg/mL. These differences were statistically significant for hs-CRP (F=19.56, p<0.001), IL-6 (F=22.54, p<0.001) and TNF-alpha (F=32.91, p<0.001) (Table 6; Figure 4).

Table 6: Comparison of inflammatory markers across pathological classes

Values are expressed as mean ± SD. One-way ANOVA was used. hs-CRP: high-sensitivity C-reactive protein; IL-6: interleukin-6; TNF-alpha: tumour necrosis factor-alpha.

Figure 4: Inflammatory marker levels across pathological classes

Association of hs-CRP with Advanced Pathological Lesions

Elevated hs-CRP was significantly associated with advanced pathological disease. Among patients with raised hs-CRP, 38 of 60 patients (63.3%) had class III or class IV lesions, compared with 20 of 50 patients (40.0%) among those with lower hs-CRP values. This association was statistically significant (χ²=5.06, p=0.025) (Table 7).

Table 7: Association of hs-CRP status with advanced pathological lesions

Data are expressed as n (%). Chi-square test was used. hs-CRP status was categorised according to laboratory reference cut-off

Tubulointerstitial and Vascular Lesions

Tubulointerstitial fibrosis and tubular atrophy were more frequent in patients with advanced pathological classes. Moderate-to-severe interstitial fibrosis/tubular atrophy was present in 41 patients (37.3%). Arteriolar hyalinosis was observed in 72 patients (65.5%), and arteriosclerosis was seen in 58 patients (52.7%). Patients with moderate-to-severe interstitial fibrosis had higher mean HbA1c, triglycerides, LDL cholesterol, hs-CRP, IL-6 and TNF-alpha compared with those having absent or mild fibrosis (Table 8; Figure 5).

Table 8: Association of biochemical markers with tubulointerstitial fibrosis/tubular atrophy

Values are expressed as mean ± SD. Independent samples t-test was used. IFTA: interstitial fibrosis/tubular atrophy.

Figure 5: Frequency of tubulointerstitial and vascular lesions across pathological classes

Correlation Analysis

HbA1c showed a positive correlation with pathological severity score, urine albumin-creatinine ratio, hs-CRP and IL-6, and a negative correlation with eGFR. Triglycerides and LDL cholesterol also showed positive correlations with pathological severity. Among inflammatory markers, TNF-alpha showed the strongest correlation with pathological severity, followed by IL-6 and hs-CRP (Table 9).

Table 9: Correlation of biochemical markers with pathological severity score

Pearson correlation analysis was used. Positive r-value indicates direct correlation; negative r-value indicates inverse correlation.

The present study evaluated the association of HbA1c, lipid profile and inflammatory markers with renal pathological changes in diabetic nephropathy. The findings showed that higher HbA1c, atherogenic lipid abnormalities and increased inflammatory markers were significantly associated with advanced diabetic nephropathy lesions. Patients with class III and class IV disease had higher HbA1c, total cholesterol, triglycerides, LDL cholesterol, hs-CRP, IL-6 and TNF-alpha, along with lower HDL cholesterol and eGFR. Poor glycaemic control showed a clear relationship with histological severity. Patients with HbA1c ≥9.0% had a greater frequency of class III and class IV lesions. This observation supports the biological role of chronic hyperglycaemia in renal structural injury. Persistent hyperglycaemia can lead to non-enzymatic glycation of proteins, activation of protein kinase C, increased oxidative stress and stimulation of profibrotic pathways. These processes contribute to mesangial expansion, thickening of the glomerular basement membrane and progressive glomerulosclerosis. The lipid profile findings also demonstrated a significant association with renal pathological severity. Total cholesterol, triglycerides and LDL cholesterol increased progressively from class IIa to class IV, whereas HDL cholesterol declined. Dyslipidaemia was significantly associated with advanced pathological lesions. These findings suggest that lipid-mediated injury may contribute to diabetic renal damage. Lipid accumulation within renal cells can promote oxidative stress, tubular epithelial dysfunction, macrophage activation and interstitial fibrosis. In clinical practice, lipid abnormalities are often treated mainly for cardiovascular risk reduction, but the present findings support their relevance in renal disease progression as well. Inflammatory markers showed strong associations with diabetic nephropathy severity. hs-CRP, IL-6 and TNF-alpha were significantly higher in advanced pathological classes. Raised hs-CRP was significantly associated with class III and class IV disease. These findings are consistent with the concept that diabetic nephropathy is not merely a metabolic or haemodynamic disorder but also involves chronic inflammatory activation. IL-6 and TNF-alpha can promote endothelial dysfunction, increase vascular permeability and stimulate extracellular matrix deposition. Their elevation in advanced lesions may reflect both systemic inflammation and intrarenal inflammatory activity. Tubulointerstitial fibrosis and tubular atrophy showed significant association with HbA1c, lipid abnormalities and inflammatory markers. This is clinically important because tubulointerstitial damage often correlates closely with renal functional decline. Patients with moderate-to-severe fibrosis had higher HbA1c, triglycerides, LDL cholesterol, hs-CRP, IL-6 and TNF-alpha. This finding suggests that metabolic and inflammatory stress may contribute not only to glomerular damage but also to tubular and interstitial injury. The inverse relationship between eGFR and pathological severity was expected. As pathological class advanced, eGFR declined and urine albumin-creatinine ratio increased. However, the study also showed that biochemical markers had meaningful associations with renal structural damage. This indicates that HbA1c, lipid profile and inflammatory markers may provide useful supportive information when assessing patients at risk of advanced diabetic nephropathy. The study has clinical relevance. In patients with diabetes and renal involvement, routine biochemical markers may help identify those who are more likely to have advanced renal injury. HbA1c and lipid profile are widely available, inexpensive and routinely measured. hs-CRP is also easily accessible in many laboratories. IL-6 and TNF-alpha may not be routinely available in all settings, but they provide useful insight into the inflammatory burden of disease. A combined approach using glycaemic, lipid and inflammatory assessment may improve risk stratification. The study also highlights the value of renal biopsy in selected diabetic patients. While many cases of diabetic kidney disease are diagnosed clinically, biopsy provides direct evidence of structural damage and helps distinguish diabetic nephropathy from non-diabetic renal disease. In biopsy-proven cases, pathological classification gives a more precise understanding of disease severity and may guide prognosis. Limitations This study had certain limitations. It was a single-centre observational study with a moderate sample size. Because the study was cross-sectional, causal relationships could not be established. Renal biopsy was performed only in clinically indicated cases; therefore, selection bias may have been present. Serial changes in HbA1c, lipid profile and inflammatory markers were not assessed. Long-term renal outcomes such as progression to end-stage renal disease were not evaluated. Further multicentre prospective studies with follow-up data are required to validate these findings.

The present study showed a significant association between poor glycaemic control, dyslipidaemia, inflammatory marker elevation and advanced pathological changes in diabetic nephropathy. Higher HbA1c, increased total cholesterol, triglycerides, LDL cholesterol, hs-CRP, IL-6 and TNF-alpha were associated with class III and class IV lesions, tubulointerstitial fibrosis and vascular changes. HDL cholesterol and eGFR showed inverse relationships with pathological severity. These findings suggest that combined assessment of HbA1c, lipid profile and inflammatory markers may help identify diabetic patients at greater risk of progressive renal structural damage.

1. Tervaert TWC, Mooyaart AL, Amann K, Cohen AH, Cook HT, Drachenberg CB, et al. Pathologic classification of diabetic nephropathy. J Am Soc Nephrol. 2010;21(4):556-63.
2. Kidney Disease: Improving Global Outcomes Diabetes Work Group. KDIGO 2022 Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease. Kidney Int. 2022;102(5S):S1-S127.
3. de Boer IH, Khunti K, Sadusky T, Tuttle KR, Neumiller JJ, Rhee CM, et al. Diabetes management in chronic kidney disease: a consensus report by the American Diabetes Association and Kidney Disease: Improving Global Outcomes. Diabetes Care. 2022;45(12):3075-90.
4. Fioretto P, Mauer M. Diabetic nephropathy: diabetic nephropathy, challenges in pathologic classification. Nat Rev Nephrol. 2010;6(9):508-10.
5. Alicic RZ, Rooney MT, Tuttle KR. Diabetic kidney disease: challenges, progress and possibilities. Clin J Am Soc Nephrol. 2017;12(12):2032-45.
6. Donate-Correa J, Martín-Núñez E, Muros-de-Fuentes M, Mora-Fernández C, Navarro-González JF. Inflammatory cytokines in diabetic nephropathy. J Diabetes Res. 2015;2015:948417.
7. Donate-Correa J, Luis-Rodríguez D, Martín-Núñez E, Tagua VG, Hernández-Carballo C, Ferri C, et al. Inflammatory cytokines in diabetic kidney disease: pathophysiologic and therapeutic implications. Front Med. 2021;7:628289.
8. Samsu N. Diabetic nephropathy: challenges in pathogenesis, diagnosis, and treatment. Biomed Res Int. 2021;2021:1497449.
9. Jung CY, Yoo TH. Pathophysiologic mechanisms and potential biomarkers in diabetic kidney disease. Diabetes Metab J. 2022;46(2):181-97.
10. Kawanami D, Matoba K, Utsunomiya K. Dyslipidemia in diabetic nephropathy. Ren Replace Ther. 2016;2:16.
11. Palazhy S, Viswanathan V. Lipid abnormalities in type 2 diabetes mellitus patients with overt nephropathy. Diabetes Metab J. 2017;41(2):128-34.
12. Navarro-González JF, Mora-Fernández C. The role of inflammatory cytokines in diabetic nephropathy. J Am Soc Nephrol. 2008;19(3):433-42.
13. Navarro-González JF, Mora-Fernández C, Muros de Fuentes M, García-Pérez J. Inflammatory molecules and pathways in the pathogenesis of diabetic nephropathy. Nat Rev Nephrol. 2011;7(6):327-40.
14. Wada J, Makino H. Inflammation and the pathogenesis of diabetic nephropathy. Clin Sci. 2013;124(3):139-52.
15. Lin JS, Susztak K. Podocytes: the weakest link in diabetic kidney disease? Curr Diab Rep. 2016;16(5):45.
16. Reidy K, Kang HM, Hostetter T, Susztak K. Molecular mechanisms of diabetic kidney disease. J Clin Invest. 2014;124(6):2333-40.
17. Forbes JM, Cooper ME. Mechanisms of diabetic complications. Physiol Rev. 2013;93(1):137-88.
18. Thomas MC, Brownlee M, Susztak K, Sharma K, Jandeleit-Dahm KA, Zoungas S, et al. Diabetic kidney disease. Nat Rev Dis Primers. 2015;1:15018.
19. Afkarian M, Zelnick LR, Hall YN, Heagerty PJ, Tuttle K, Weiss NS, et al. Clinical manifestations of kidney disease among US adults with diabetes, 1988-2014. JAMA. 2016;316(6):602-10.
20. Rossing P, Caramori ML, Chan JCN, Heerspink HJL, Hurst C, Khunti K, et al. Executive summary of the KDIGO 2022 Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease. Kidney Int. 2022;102(5):990-9.