Evaluation of Enzymatic Sarcosine Oxidase Method and Comparison with Modified Kinetic Jaffe’s Reaction Analytical Method for Quantitative Analysis of Creatinine

Abstract

Kidneys are body organs located on the right and left side of the abdomen. Millions of nephrons are found in a kidney and are both structural and functional units of the organ. They remove waste products like creatinine from blood and passes it out through urine. Creatinine as a waste product of metabolism is a breakdown product of creatine phosphate found in body muscles. Most of the creatinine is excreted via the kidneys, therefore serum creatinine estimation is part of the renal function tests which determine the kidney function. Methods of creatinine estimation are grouped into chemical, enzymatic and spectrometry methods. The objective of this study was to evaluate the enzymatic sarcosine oxidase analytical method and compare it with the modified kinetic Jaffe’s method for quantification analysis of creatinine. It was a cross – sectional study with a population of 384 participants grouped into 213 blood donors, 104 renal disordered patients and 67 liver disordered patients randomly selected from blood transfusion unit, renal unit and medical ward of the Kenyatta National Hospital respectively. The study was in 3 phases. The evaluation phase included individual specimen precision test using 10 specimens of extremely low and high serum creatinine levels. Then precision on within run, between run and between days modes of analyses where two specimens, one with low serum creatinine of 30 μmol/L and another with high serum creatinine of 4769 μmol/L were analysed. 67 icteric specimens were analysed for total bilirubin and serum creatinine using the two methods for substance interference. Phase 2 was to compare the quantitative serum creatinine results of the 232 specimens analysed using the two creatinine analytic methods. Reference ranges phase for serum creatinine and estimated creatinine clearance using serum creatinine results of 213 (male: 118; female: 95) healthy subjects was performed and determination of glomerular filtration rate done using same number of participants. The enzymatic sarcosine oxidase method had a good precision and performance compared to the modified kinetic Jaffe’s method with standard deviation (SD) of <1. The three modes of analyses, the SD variation was < 1.6 μmol/L for the low serum creatinine level and < 4 μmol/L for the high serum creatinine level. Bilirubin levels affected the sensitivity of creatinine analysis using the modified kinetic Jaffe’s reaction with no effect on the enzymatic sarcosine oxidase method, with p = 0.013 at 95% Confidence Interval (CI). The two serum creatinine analytical methods compared significantly different with p=0.04 at 95% CI. Reference ranges for serum creatinine using the enzymatic sarcosine oxidase method for male and female were [40.12 – 108.48] μmol/L and [31.1 – 93.5] μmol/L respectively with p = 0.002 at 95% CI while estimated creatinine clearance were [63.92 – 135.88] ml/min and [71.36 – 130.64] ml/min for male and female respectively with p = 0.03 at 95% CI. The glomerular filtration rate values for the normal adults were estimated at ≥ 99.9 ml/min and ≥ 101.0 ml/min for male and female respectively with p = 0.021. Therefore the enzymatic sarcosine oxidase method was recommended as a method of choice for estimation of serum creatinine and determination of glomerular filtration rate for accurate diagnosis of kidney disorders and appropriate categorization of chronic kidney disorders for the Kenyan population.