Evaluation of kidney disease using e-GFR compared to measured creatinine clearance

Measurement of renal function is required for diagnosis and stratification of kidney disease. GFR is considered as the best overall measure of kidney function for diagnosis and treatment of patients with CKD. Measuring GFR is time consuming and hence eGFR is calculated using equations with endogenous markers like SCr. Therefore, it is of interest to examine the accuracy of creatinine based estimates (CrCl and CG formula) of GFR among patients. Thus, 60 in-patients (30 men and 30 women) at the GVP hospital and 40 controls were enrolled in the study. SCr and 24 hrs urine creatinine are estimated using blood sample and same day 24-hr urine collection. SCr is estimated using the Kinetic Jaffe's method in Auto analyzer for serum and urine. eGFR is calculated using the CG formula for the SCr value. We evaluated the correlation between measured CrCl derived from 24-hr urine collection and calculated/predicted CrCl using the CG equations. A positive correlation was observed between measured GFR and e-GFR in case and control groups.


Background:
Chronic kidney disease (CKD) is a progressive disease involving the irreversible loss of kidney function over the time [1].Under normal physiologic conditions, the kidneys serve several functions: such as regulation of fluid volume, acid base balance of plasma, excretion of nitrogenous waste, synthesis of erythropoietin, 1,25-dihydroxy-cholecalciferol, and renin, and different drug metabolism.However, due to progression of renal dysfunction CKD is associated with multiple physiological and metabolic disturbances, such as-worsening and eventual failure of kidney function, accumulation of uremic toxins, metabolic acidosis, abnormalities in lipid, amino acid, mineral metabolism, malnutrition, insulin resistance, inflammation, oxidative stress, anaemia, vitamin D deficiency, skeletal muscle dysfunction, hypertension, and anorexia-Cachexia which are linked to poor outcomes [2].Chronic Kidney Disease (CKD) is defined as kidney damage of three or more months duration caused by structural or functional abnormalities with or without a decreased glomerular filtration rate (GFR).Pathological markers, abnormalities in the blood or urine, or imaging tests, may reveal kidney dysfunction [3].CKD was defined as creatinine clearance (CrCl) or GFR less than 60 ml/min/1.73m 2 [4, 5] here are, three equations in use to estimate eGFR: Four-variable MDRD equation [6, 7] CKD-EPI equation [8] and Cockcroft-Gault equation [9].The KDIGO recommends that CKD be diagnosed, classified, and staged by GFR [10].In clinical practice GFR is crucial for diagnosis, management, drug dosing and prognosis, in addition to its utility for research and public health [11, 12 & 13].The national kidney foundation kidney disease outcomes quality initiative (NKF-K/DOQI) framed a classification system that has become widely adopted in clinical practice (   2.00 SD-Standard deviation, IQR-Interquartile range, (S): Significant (p<0.001)P-value means the probability of obtaining results at least as extreme as the observed results of a statistical hypothesis test, assuming that the null hypothesis is correct.

Materials and methods: Materials:
This study was conducted at the Department of Biochemistry, Gayatri Vidya Parishad Hospital and Medical College (GVPIHC&MT) Visakhapatnam, Andhra Pradesh, India.Written informed consent was obtained from all subjects enrolled.The study was approved by the Institutional Ethical Committee (IEC).

Subjects:
Patients attending the Department of Nephrology, Gayatri Vidya Parishad Hospital, with established diagnosis of CKD were subjects of the study.A total of (n=60) CKD patients were included in the study.Patients were classified into various stages of CKD (30 men and 30 women) based on GFR (calculated from serum creatinine, using cockcroft-gault (CG) equation.Healthy volunteers (n=40) who were enrolled in this study served as controls.

Sample Collection:
Two micro litre of blood was drawn and transferred into a plain tube .collectedfrom all the participants.Samples were separated by centrifugation and stored at -50o C until further biochemical analysis.

Statistical analysis:
Data were entered in MS-Excel and analyzed in SPSS V25.Descriptive statistics were represented with percentages, Mean with SD or Median with IQR depends on nature of the data.Shapiro wilk test was applied to find normality.Chi-square test, Mann-whitney U test, Spearman correlation were applied.P<0.05 was considered as statistically significant.

GFR Cockcroft -Gault Equation:
Mg of substance excreted per minute in urine clearance = Mg of substance per ml of plasma C = U x V/P =ml/mt

Results:
The renal images of CKD patients from whom the samples were collected and analyzed (data not shown -check with authors).Table 2 shows that maximum and minimum age group ranges in cases were 32-80 years and in controls were 22-29 years range.The mean age ± SD in cases was 56.23 ± 10. 44 and in controls was 24.98 ± 1. 88. Table 3 shows that among a total of 60 cases & 40 controls, 50% of cases are females and remaining 50% of cases are males.Out of 40, 50% of controls are females and remaining 50% of are males.Equal distribution among cases and controls was maintained.Table 4 shows that the maximum weight in group cases is 78 kgs and controls are 75 kgs.Weight (Mean ± SD) in case group is 60.68 ± 6.90 and in the control group the weight (Mean ± SD) is 58.90 ± 6.48.Table 5 shows that maximum range of serum creatinine in cases is 9.65 mg/dl and controls are 0.60 mg/dl.Mean ± SD of serum creatinine in case group is 5.82 ± 1.29 and in control group Mean ± SD is 0. 87±0.16.Table 6 shows that maximum range of urinary creatinine in cases is 89.00mg/dl and controls are 97.60 mg/dl.Mean ± SD of urinary creatinine in case group is 62. 58 ± 15.99) and in control group is mean ± SD is 97.60 ± 12.67.Table 7 shows that maximum range of urinary volume in cases is 3000ml and controls are 2300 (ml).Mean ± SD of urine volume in case group (3000 ± 491.16), whereas in control group, Mean ± SD (2300 ± 228.69).Table 8 shows that maximum range of eGFR in cases is 27.26 (ml/min/1.73 m 2 ) and controls is 136.96(ml/min/1.73 m 2 ).Mean ± SD of eGFR in case group is 27.26 ± 3.75) and in control group mean ± SD is 136.96 ± 11.37.Table 9 shows that maximum range of CG in cases is 28.16 (ml/min/1.73 m 2 ) and controls is 127.78 (ml/min/1.73 m 2 ).Mean ± SD of CG in case group is 28.16 ± 3.86 and in control group mean ± SD is 127.78 ± 16.42.Table 10 shows the positive and significant correlation between the variables of both control and cases.

Conclusion:
Data shows that e-GFR obtained by cockcroft gault using creatinine value is having good correlation with measured GFR using serum creatinine and 24 hrs urine creatinine profile.Thus, e-GFR is useful for the evaluation of kidney disease in hospital setting.

14, 15 & 16]. Therefore
, it is of interest to determine the utility of eGFR in comparison to measured creatinine clearance in the evaluation of kidney disease.

Table 1 :
The 5 Stages of CKD defined by Estimated Glomerular Filtration Rate [

Table 2 :
Comparison of the Variable AGE (in Years) in Controls and CKD patients

Table 3 :
Distribution of Gender (Female & Male) in controls and CKD patients

Table 4 :
Comparison of variable (weight) in controls and CKD patients

Table 5 :
Comparison of the variable serum creatinine (in mg/dl) in controls and CKD patients

Table 6 :
Comparison of the variable urine creatinine (mg/dl) in CKD patients

Table 7 :
Comparison of the variable urine volume (in ml/24hrs) CKD patients & controls

Table 8 :
Comparison of the variable eGFR (ml/mt) in controls and CKD patients

Table 9 :
Comparison of the variable (Cockcroft -Gault) in controls and CKD patients

Table 10 :
Correlation between variables of (eGFR and Cockcroft Gault) in (controls and CKD patients) SD of CG in case group is 28.16±3.86)and in control group, the mean ± SD is 127.78±16.42.This is in accordance with Kumar et al. [21] that showed the creatinine based GFR estimation provides a more accurate assessment of 24 hour creatinine clearance and kidney function.Thus, the use of Cockcroft-Gault formulae in estimating GFR for drug dosing, detection of CKD and for prognosis is evident.Further, a positive linear correlation between mGFR & eGFR and Cockcroft gaunt in controls and CKD patients in accordance with Kumar et al. [21] is observed.
[22].Data shows that among 60 subjects, the maximum range of urinary volume in cases is 3000 ml and controls is 2300ml.Mean ± SD of urine volume in case group is 3000 ±491.16andwhereas in control group the mean ± SD is 2300 ± 228.69.This is in accordance with Xu et al.[22].Data shows that among 60 subjects the maximum range of eGFR in cases is 27.26 (ml/min/1.73m2) and controls is 136.96(ml/min/1.73m2).The mean ± SD of eGFR in case group is 27.