Comparison of 150mmol/L and 250mmol/L concentration of sodium hydroxide in Jaffe's two point method for serum creatinine measurement with respect to linearity of assay

Abstract

Objectives: Objective of the study is to perform linearity check for Creatinine measurement with Jaffe's two point method using CLSI EP-6 guideline for 150 mmol/L, 250mmol/L NaOH concentration in final reagent mixture. Material & Method: Leftover serum of samples received by the laboratory, devoid of patient identification, was used to make pool of serum. Serum creatinine reagents have NaOH of 150 mmol/L, 250 mmol/L were prepared. Serial dilution of pooled serum spiked with creatinine powder was prepared. Creatinines were measured in series of dilution. Linear regression analysis of each dilution series to find linearity limit was performed. esult & Discussion: This study evaluated Linearity difference plot using CLIA criteria (15% or 0.3 mg/dl whichever is higher) for creatinine at 95% confidence limit.7.5% of result or 0.15 mg/dl were used for plotting Linearity Difference plot. If any the two conditions are satisfied at a given point in the Linearity Difference Plot, the point is considered within linearity. 250 mmol/L NaOH in final reagent mixture gives limit of linearity 23.77mg/dl and 150 mmol/L NaOH in final reagent mixture gives limit of linearity 31.16 mg/dl. Conclusion: 150 mmol/L final reagent concentration of NaOH gives higher linearity of 31.16 mg/dl, low slop (a=29.23) indicating high sensitivity of the reagent, low y-intercept (b=-0.4578) indicating minimum effect of non-creatinine chromogens; i.e. high specificity than 250mmol/L final reagent concentration of NaOH.