Comparision of creatinine levels measured by liquid chromatography-mass spectrometry and routine spectrophotometric methods and evaluation of their effects on GFR calculation

Kidney Diseases and especially Chronic Kidney Failure, which has chronic, progressive and irreversible loss of functional nephrons due to various reasons, is an important public health problem in all over the world and in our country. Since renal failure is a condition that can be prevented or delayed, therefore it is important to detect and monitor kidney function and glomerular filtration rate (GFR) with accurate markers. Because of direct GFR measurement is difficult and also labored, estimated GFR is widely used instead. Creatinine is the only parameter that can be measured biochemically in the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, which is one of the accepted over fourty eGFR equations that recommended for international and national use. Repeated measurement of serum creatinine levels is considered a sufficient parameter in monitoring GFR. Therefore, creatinine levels should be analyzed with high sensitivity in terms of determining kidney function. Jaffe method is mostly used in clinical laboratories for creatinine analysis and is based on spectrophotometric measurement of creatinine, which gives color with picric acid at alkaline media. Such as proteins, bilirubin and ketones substances can interfere with this method and cause false results. Further, sensitivity of the performed method is critical for accurate results in low creatinine values range. Therefore, creatinine is a commonly used clinical parameter, yet research on the accuracy of the measurement method remains current. Limitations in accuracy and precision in creatinine measurement have led to the search for new biomarkers. Low molecular weight proteins such as cystatin C, Beta Trace Protein (BTP) and Symmetric-Dimethyl Arginine (SDMA) are recommended as an renal marker as an alternative to creatinine. Among these, GFR calculation formulas related to cystatin C, which is the most preferred in routine use, are also recommended by our Ministry of Health. In our study, we determined liquid-chromatography mass spectrometry (LC-MS / MS) measurement method as the reference method for ease of sample preparation and use, rapid results, and high sensitivity for creatinine quantification. After LC-MSMS creatinine method validation studies, we also compared the results of Jaffe method and enzymatic method with creatinine results. We examined the effect of the obtained results on CKD-EPI eGFR calculation. In order to examine the accuracy of these data, we also used standard reference material SRM 967a with different creatinine methods. As an alternative marker, we analyzed cystatin C and BTP by nephelometer (BNII, Siemens) and SDMA by LC MS / MS. Then, we compared the results with creatinine measurement using reference method LC MS / MS. Also, after calculating the cystatin C results with the cystatin C based eGFR and also the combined eGFR equation with cystatin C and creatinine, we compared the results with the commonly used CKD-EPI. We examined the effect of all eGFR results obtained on classification of chronic renal failure. As a result of our reference LC-MS / MS creatinine method, for accuracy study two levels (0.85 mg / dL and 3.87 mg / dL) of the SRM967a material we used concentrations were 0.84 mg/dL and 3.95 mg/dL respectively. Compared to the reference LC-MS / MS method, we found a strong correlation with Jaffe and enzymatic creatinine methods and obtained consistent results in regression analysis. We obtained a positive correlation with cystatin C, BTP and SDMA we determined as an alternative biomarkers, with high correlation with cystatin C (r 2 = 0.91). Three methods (LC-MSMS referance creatinine analyze method, eGFR equation and creatinine/cystatin C combined eGFR equation) has showed consistent regression and strong corelation in creatinine results. It is recommended that the methods of the tests, which are important for clinical decision, to be standardized between the laboratories. Standard reference materials (SRM) or a reference method can be used for standardization. Although the Jaffe method we use in the routine method gives consistent results with the reference method, because may cause high standard deviations in the eGFR results and differences in classification of chronic renal failure, we recommend verifying with reference method or SRMs. Cystatin C, which is used as an alternative marker, can give more accurate and harmonious results when combined with creatinine in eGFR equation. As a result of our study, LC-MS / MS may be routinely used for creatinine measurements, since a high-sensitive creatinine (hs-creatinine) method is needed for low creatinine levels, such as in pediatric and geriatric patients.