European Journal of Cardiovascular Medicine

CKD is now considered as major public health importance worldwide because of the critical combination of an increased disease prevalence with remarkable harmful effects on prognosis and quality of life, and too on economic resources.¹ The reported prevalence of CKD in different regions of India ranges from,1% to 13%, and recently, data from the International Society of Nephrology’s Kidney Disease Data Center Study reported a prevalence of 17%.²

Chronic kidney disease is often symptomless in its early stages & goes undetected until it is very advanced. It is important to identify factors that increase CKD risk, even in individuals with normal GFR. Risk factors include hypertension, diabetes mellitus, autoimmune disease, age>60yrs, a family history of renal disease, a previous episode of acute kidney injury, and the presence of proteinuria, abnormal urinary sediment, or structural abnormalities of the urinary tract.³

Progression of CKD is associated with a number of serious complications, including increased incidence of cardiovascular disease, hyperlipidemia, anemia, and metabolic bone disease.⁴ Uromodulin (UMOD) is a Zona pellucida-like domain containing glycoprotein which is encoded by the UMOD gene located on chromosome 16.⁵ Uromodulin is the matrix of urinary casts which is derived from the secretion of renal tubular cells. In addition to its tubular secretion, Uromodulin also gets released from the tubular cell’s basolateral side into the interstitium. ⁶ Present study was aimed to study serum uromodulin as a biomarker of kidney function in patients with CKD and to identify early stages of chronic kidney disease.

Present study was single-center, prospective, observational study, conducted in department of biochemistry, at Thanjavur Medical College Hospital, Thanjavur, India. Study duration was of 2 years (January 2020 to December 2021). Study approval was obtained from institutional ethical committee.

Inclusion criteria

• Patients older than 18 years age, with chronic kidney disease, willing to participate in present study

Exclusion criteria

• Acute coronary syndrome
• Diabetes mellitus
• Renal transplantation
• Significant hepatic dysfunction
• Known or treated malignancies

Under aseptic precautions, 5ml of venous blood sample was collected after overnight fasting of 12 hours from all subjects. All samples were allowed to clot for 2 hours at room temperature before centrifugation. After retraction of the clot, samples were centrifuged at 1000×g for 20 minutes for separation of serum.

The data were entered in MS office excel sheet and analyzed using SPSS version 16. Continuous data with normal distribution was expressed as mean with standard deviation. Categorical data were expressed as frequency with %. Fisher’s exact test was used to compare the frequency between the groups. Unpaired ‘t’ test was used to compare the means between the controls and cases. One-way ANOVA with Bonferroni post hoc test was used to compare the variances between the six groups. Pearson’s correlation was used to determine the direction and degree of association between the parameters. P <0.05 was considered statistically significant.

A total of 180 subjects were selected as the study group for the present study. This includes 150 cases with Chronic Kidney Disease and 30 healthy controls. Levels of serum Uromodulin, Urea, Creatinine, Fasting, and Postprandial Blood Sugar were estimated for all the samples of the study group. eGFR was calculated from the CKD-EPI formula. The values obtained in controls and cases are presented in table 1.

Table 1: Demographic characteristics and kidney function parameters

There were no significant differences in the gender distribution. There is no difference in mean BMI in cases (25.1 ± 1.7) and in controls (25.2 ±2.8) and it is not statistically significant. (p-value >0.05). There was an increase in the mean SBP in cases (123± 9.4) when compared to controls (115±9.3) and there was an increase in the mean DBP in cases (83.16±7.58) when compared to controls (79.2±4.67), which is found to be statistically significant (p-value < 0.001). There were no significant differences in the mean of FBS and PPBS in cases when compared to control and p>0.05 which was considered as statistically insignificant.

Table 2: Comparison of various parameters among cases and controls

 There was an increase in the mean blood urea level in cases (63.1±23.9) when compared to controls (25.8 ±5.7), which is statistically significant (p-value < 0.001) and there was an increase in blood urea level with progressive stages of CKD. One Way ANOVA with Bonferroni Post hoc test was used to compare the variance between healthy control & different stages of CKD, which shows the significant difference (p,0.001).

Table 3A: Comparison of Blood urea levels between control and cases

Table 3B: Comparison of Blood urea levels between control group and various stages of CKD

Table 3C: Comparison of Blood urea levels between groups

There was an increase in mean serum creatinine levels in cases (0.7±0.08), when compared to controls (2.1±1.4) which are statistically significant (p<0.001). It also shows statistical significance(p<0.001) when compared with adjacent stages of CKD.

Table 4A: Comparison of serum creatinine levels between control and cases

Table 4B: Comparison of serum creatinine levels between control group and stages of CKD

Table 4C: Comparison of serum creatinine levels between groups

eGFR was significantly lower in cases (48.8±31) than in control (109.3±4.9). It shows statistical significance(p<0.001) when compared with adjacent stages of CKD.

Table 5A: Comparison of eGFR levels between control and cases

Table 5B: Comparison of eGFR levels between control group and stages of CKD

Table 5C: Comparison of eGFR levels between groups

Serum Uromodulin concentrations were gradually decreased with progressive stages of CKD, ranging from a maximum of 107.1ng/ml in CKD I to a minimum of 7.8ng/ml in CKD V. When comparing Serum Uromodulin levels between healthy control & different stages of CKD, it shows a significant difference (p<0.0001). Comparing adjacent stages of CKD, a significant difference is detected for all pairs of CKD stages. (p<0.0001) by using One Way ANOVA with Bonferroni Post hoc test.

Table 6A: Comparison of Serum Uromodulin levels between control and cases

Table 6B: Comparison of Serum Uromodulin levels between control group and stages of CKD

Table 6C: Comparison of Serum Uromodulin levels between groups

Upon univariate analysis, Serum Uromodulin concentrations were significantly associated with all biomarkers and eGFR. eGFR, (r = 0.866); Urea (r = -0.783), creatinine (r = -0.686). There was a significant negative correlation between Serum Uromodulin with SBP, Serum creatinine, Blood urea, and a positive correlation with eGFR.

Table 7: Correlation of various parameters with respect to uromodulin (ng/ml) levels

FIGURE 1                                             FIGURE 2                                 FIGURE 3

FIGURE 1: Correlation of Serum Uromodulin vs eGFR

FIGURE 2: Correlation of Serum Uromodulin vs Blood Urea

FIGURE 3: Correlation of Serum Uromodulin vs Serum Creatinine

Chronic kidney disease is a clinical syndrome that occurs when there is a gradual decline in renal function over time and mortality rises in parallel to the deterioration of kidney function. Therefore, early detection of CKD and an accurate assessment of kidney function in order to initiate actions to prevent a further decline are important.

Current assessment of kidney function relies primarily on measurements of conventional biomarkers of kidney function such as creatinine (Cr), blood urea nitrogen (BUN), and cystatin C (CyC), all of them having crucial limitations (e.g. serum creatinine concentrations tend to rise only when approximately 40% to 50% of renal parenchyma is reversibly or irreversibly damaged). Therefore, early stages of chronic renal failure are often overlooked, a circumstance that delays possible diagnostic and therapeutic interventions.

In the present study, Serum Uromodulin concentrations were found to be significantly (p<0.0001) decreased in patients with different stages of Chronic Kidney Disease; stage I (115±17.3), stage II (89.7±17.6), stage III (62.7±13.4), stage IV (39.1±13.2), stage V (19.5±7.9), when compared to the control group (225.9±42.2). Thereby this study confirms the previous studies that showed decreased levels of Uromodulin in CKD patients.^7,8,9

When patients in different stages of CKD were compared, Serum Uromodulin levels were found to be progressively decreased from stage 1 to stage 5. This observation shows that Serum Uromodulin decreases as renal function declines and positively correlated with eGFR (r= 0.866). Uromodulin allowed to distinguish between normal individuals(control) and patients at all stages of CKD, especially at early stages of kidney disease (CKD I) by simply assessing plasma concentrations, at a reasonable level of sensitivity and specificity outperforming all other biomarkers tested in this study.

Serum Creatinine and Blood Urea were progressively increased in cases than controls and shows a negative correlation with Uromodulin (r = -0.686 and r =-0.783) respectively. Serum Uromodulin is a direct marker for the number of intact tubular cells of the ascending limb (where it is exclusively produced) and therefore may represent a marker for the number of remaining functional nephrons/renal tissue/tubular secretion which in turn potentially helps the treating physician to assess the kidney function in the phase when conventional markers/glomerular filtration fails to indicate deterioration of kidney function.⁷

Limitations of present study were, small sample size. There was a lack of a gold standard such as inulin clearance or measured Cr clearance for GFR measurement. Other valuable relevant markers like Cystatin C are not included in the study.

There is scope for future study as Serum UMOD as a screening tool for evaluating CKD risk, cardiovascular complications, possibly overall mortality, novel predictive biomarker for renal function and for the incidence of CKD. These preliminary results encourage further evaluation of Uromodulin in larger CKD cohorts and other clinical settings such as acute renal failure.

The present study demonstrated that serum Uromodulin levels are significantly decreased progressively from stage 1 to 5, in patients with Chronic Kidney Disease as renal function declines. Serum uromodulin is a promising biomarker for the assessment of kidney function. It uniquely allows the identification of early stages of CKD when conventional biomarkers of kidney function, which are all markers of glomerular filtration, are still within the normal range. Thus, Serum Uromodulin can be used as a biomarker to detect early stages of Chronic Kidney Disease.

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