Type 2 diabetes mellitus (T2DM) is a major metabolic disorder characterized by chronic hyperglycemia and insulin resistance and is associated with progressive microvascular and macrovascular complications. Current diagnostic criteria emphasize plasma glucose and glycated hemoglobin (HbA1c), with HbA1c also providing an assessment of long-term glycemic exposure.[1] India carries a substantial burden of diabetes and other metabolic non-communicable diseases, highlighting the need for readily available biomarkers that may help identify patients at increased risk of complications.[2]

Persistent poor glycemic control is strongly related to diabetic complications. Long-term variability and elevation of HbA1c have been associated with increased microvascular risk in patients with T2DM.[3] Intensive glycemic control can reduce several microvascular outcomes, emphasizing the importance of sustained glucose management.[4] Furthermore, HbA1c variability may modify the effect of glycemic control on microvascular complications.[5]

Insulin resistance and dyslipidemia are closely linked in T2DM, and reduced high-density lipoprotein cholesterol (HDL-C) is a common metabolic abnormality. In addition, measures derived from HbA1c may provide information regarding individual susceptibility to vascular complications beyond conventional glycemic assessment.[6] Oxidative stress is another important mechanism implicated in diabetic vascular injury and particularly in the development and progression of diabetic kidney disease.[7] Gamma-glutamyl transferase (GGT), an enzyme involved in glutathione metabolism, may therefore provide additional information regarding oxidative and metabolic disturbances.

The present study was undertaken to evaluate the association of HDL-C, HbA1c, and GGT in patients with T2DM and to assess their relationship with albuminuria as an indicator of diabetic microvascular involvement.

Study Design and Setting This hospital-based observational study was conducted at a tertiary care hospital in India. The study included 75 adult patients with type 2 diabetes mellitus and 50 healthy age- and sex-matched controls. Study Population Adult patients aged >40 years with T2DM who fulfilled the predefined eligibility criteria were enrolled as cases. Fifty apparently healthy individuals matched for age and sex were included as controls. All participants underwent detailed history taking, clinical examination, and relevant laboratory investigations. Inclusion Criteria Adult patients aged >40 years with established type 2 diabetes mellitus were included in the diabetic group. Healthy age- and sex-matched individuals were selected as controls. Exclusion Criteria Patients with type 1 diabetes mellitus, alcohol consumption, hemolytic anemia or hemoglobinopathies, liver enzyme levels greater than three times the upper limit of normal, acute or chronic infection or vascular inflammation were excluded. Patients receiving statins, NSAIDs, corticosteroids, methotrexate, amiodarone, tamoxifen, or other potentially hepatotoxic medications were also excluded. Patients with major comorbid conditions, including coronary artery disease, cerebrovascular disease, peripheral vascular disease, chronic renal failure, malignancy, chronic liver disease, and chronic respiratory disease, were excluded. Definition of Diabetes Mellitus Diabetes mellitus was diagnosed according to the American Diabetes Association criteria. Diagnosis was based on the presence of classical symptoms of hyperglycemia with random plasma glucose ≥200 mg/dL, fasting plasma glucose ≥126 mg/dL, 2-hour plasma glucose ≥200 mg/dL following a 75-g oral glucose tolerance test, or HbA1c ≥6.5%. In asymptomatic individuals, confirmation with an additional abnormal glucose test was required. Biochemical Assessment Blood samples were collected from cases and controls for measurement of HDL-C, GGT, and HbA1c. HbA1c was quantitatively measured using a dry chemistry method with QDxA1C, with readings compared with those obtained by high-performance liquid chromatography. HDL-C and serum GGT were quantitatively determined using automated analyzers by endpoint assay with spectrophotometric measurement. Urinary albumin was assessed qualitatively using the dipstick/reagent strip method and categorized as nil, trace, 1+, 2+, or 3+. The relationships of HDL-C, HbA1c, and GGT with each other and with the grade of albuminuria were evaluated. Statistical Analysis Data were entered into Microsoft Excel and analyzed using IBM SPSS Statistics version 21.0. Categorical variables were expressed as frequencies and percentages, whereas continuous variables were presented as mean ± standard deviation (SD). Normality was assessed using the Kolmogorov–Smirnov test. Continuous variables between two groups were compared using the unpaired t-test or Mann–Whitney U test, as appropriate. Comparisons involving more than two groups were performed using one-way ANOVA or the Kruskal–Wallis test for non-normally distributed variables. Categorical variables were analyzed using the Chi-square test or Fisher's exact test. Relationships among HDL-C, GGT, and HbA1c were assessed using Pearson's or Spearman's correlation coefficient, as appropriate. A p-value <0.05 was considered statistically significant.

A total of 125 participants were evaluated, comprising 75 patients with type 2 diabetes mellitus (T2DM) and 50 healthy controls. Among the diabetic cases, 37 (49.3%) were males and 38 (50.7%) were females, whereas the control group included 25 (50.0%) males and 25 (50.0%) females. Sex distribution was comparable between the groups (p=0.942). The mean age was 56.91 ± 5.76 years among T2DM cases and 51.74 ± 5.60 years among controls (p<0.0001).

Table 1. Demographic characteristics of T2DM cases and controls

Biochemical parameters differed significantly between cases and controls. Mean HDL-C was significantly lower among patients with T2DM (36.00 ± 6.54 mg/dL) than controls (52.28 ± 2.56 mg/dL; p<0.0005). In contrast, mean GGT and HbA1c were significantly higher among diabetic patients. Mean GGT was 101.61 ± 36.84 U/L in cases compared with 19.06 ± 8.77 U/L in controls, while mean HbA1c was 9.24 ± 1.97% compared with 4.35 ± 0.94%, respectively (both p<0.0005).

Table 2. Comparison of HDL-C, GGT and HbA1c between T2DM cases and controls

Among patients with T2DM, significant relationships were observed among HDL-C, HbA1c, and GGT. HbA1c showed a significant positive correlation with GGT (r=0.479, p<0.00001), indicating higher GGT values with poorer glycemic control. HDL-C demonstrated a significant negative correlation with HbA1c (r=−0.350, p<0.005) and with GGT (r=−0.526, p<0.0005).

Table 3. Correlation among HDL-C, HbA1c and GGT in patients with T2DM

Urine albumin was absent in 27 (36.0%) diabetic patients, while 48 (64.0%) demonstrated varying degrees of albuminuria. Of the 75 cases, 17 had trace albuminuria, 14 had 1+, 13 had 2+, and 4 had 3+ albuminuria. Both GGT and HbA1c showed a significant increasing pattern with increasing grades of albuminuria. Mean GGT increased from 66.22 ± 22.14 U/L among patients without albuminuria to 145.00 ± 24.21 U/L among those with 3+ albuminuria (p<0.0001). Similarly, mean HbA1c increased from 7.99 ± 1.19% to 12.88 ± 1.40% (p<0.0001).

Table 4. Association of urine albuminuria with GGT and HbA1c among T2DM cases

Among the 75 patients with T2DM, 48 (64.0%) had albuminuria of varying grades. Both GGT and HbA1c showed an overall increasing trend with greater albuminuria severity. Mean GGT increased from 66.22 ± 22.14 U/L in patients with nil albuminuria to 145.00 ± 24.21 U/L in those with 3+ albuminuria, while mean HbA1c increased from 7.99 ± 1.19% to 12.88 ± 1.40%. These differences were statistically significant (p<0.0001), indicating that higher grades of albuminuria were associated with higher GGT and poorer glycemic control.

Type 2 diabetes mellitus is characterized by chronic hyperglycemia, insulin resistance, dyslipidemia, and oxidative stress, all of which contribute to the development of vascular complications. In the present study, patients with T2DM demonstrated significantly higher HbA1c and GGT and lower HDL-C levels compared with healthy controls. These findings are consistent with the substantial metabolic burden of diabetes reported in the Indian population and emphasize the coexistence of poor glycemic control and dyslipidemia in T2DM.[8] Mean HDL-C was significantly lower in diabetic patients than in controls (36.00 ± 6.54 vs. 52.28 ± 2.56 mg/dL; p<0.0005). Furthermore, HDL-C showed a significant negative correlation with HbA1c (r=−0.350, p<0.005). This suggests that poorer glycemic control was accompanied by lower HDL-C levels in the present population. Alterations in lipid metabolism and insulin resistance may contribute to this relationship. Mean serum GGT was markedly higher in T2DM cases than controls (101.61 ± 36.84 vs. 19.06 ± 8.77 U/L; p<0.0005). GGT also showed a significant positive correlation with HbA1c (r=0.479, p<0.00001) and a negative correlation with HDL-C (r=−0.526, p<0.0005). Dai et al. reported an association between serum GGT and diabetic nephropathy in patients with T2DM.[9] Similarly, Liang and Yang demonstrated an association between changes in the GGT/HDL-C ratio and diabetes risk, supporting the relationship between GGT, HDL-C, and metabolic abnormalities.[10] More recent evidence has also demonstrated associations between the GGT/HDL-C ratio and glycemic and metabolic status.[11-13] An important finding of the present study was that 48 (64.0%) diabetic patients had qualitative albuminuria. Mean GGT increased from 66.22 ± 22.14 U/L in patients without albuminuria to 145.00 ± 24.21 U/L in those with 3+ albuminuria. Similarly, HbA1c increased from 7.99 ± 1.19% to 12.88 ± 1.40%, with both trends being statistically significant (p<0.0001). These findings indicate that increasing albuminuria was accompanied by poorer glycemic control and higher GGT levels. Studies evaluating metabolic biomarkers and diabetic microvascular complications have similarly highlighted the importance of glycemic and metabolic abnormalities in identifying patients with greater complication burden.[14,15] The observed relationship between GGT and albuminuria is also supported by previous population-based evidence demonstrating an association between higher serum GGT and albuminuria.[16] Since GGT is involved in glutathione metabolism, its elevation may reflect metabolic and oxidative disturbances accompanying diabetes. However, the present cross-sectional study demonstrates association rather than causation. The study was limited by its relatively small sample size, single-centre design, and qualitative rather than quantitative assessment of albuminuria. The effects of duration of diabetes and antidiabetic therapy could also not be completely evaluated. Larger prospective studies using quantitative urinary albumin-to-creatinine ratio and adjustment for relevant confounding variables are required to determine the independent predictive value of HDL-C and GGT for diabetic microvascular complications.

Patients with T2DM had significantly higher HbA1c and GGT and lower HDL-C levels compared with healthy controls. HbA1c correlated positively with GGT and negatively with HDL-C, while GGT was negatively correlated with HDL-C. Increasing grades of albuminuria were associated with significantly higher GGT and HbA1c levels. These findings suggest that routinely available biochemical parameters such as GGT, HDL-C, and HbA1c may provide useful information regarding metabolic abnormalities and microvascular involvement in T2DM. Larger prospective studies are required to establish their predictive value.