Exogenous interferences with Jaffe creatinine assays: addition of sodium dodecyl sulfate to reagent eliminates bilirubin and total protein interference with Jaffe methods

Background: The study evaluated the impact of interferences on the analytical specificity of three commercial and commonly used creatinine methods (two Jaffe and one enzymatic). Methods: Manufacturer creatinine methods plus modified methods were tested with the following interferences: spiking serum with bilirubin, albumin, glucose, hemoglobin and lipid, and patient sera with maximum concentrations of bilirubin, 1,090 µmol/l and protein, 117.8 g/l. Results: Hemoglobin, 7.5 g/l and lipaemic with triglyceride concentration of 6.27 mmol/l, did not interfere with all assays. Glucose >33.3 mmol/l increased creatinine recovery for Dimension method. Samples spiked with bilirubin imparted a negative bias for Dimension and Architect methods but imparted a positive bias for Vitros assay. However, using patient sera, negative bias with bilirubin was found for all methods, from which Architect method gave the highest effect (R²=0.861), followed by Vitros (R²=0.239) and Dimension (R²=0.163). Protein provided the positive bias for all creatinine measurements that increased with increasing concentration (R² ranging from 0.104 to 0.182, P<0.0001). Addition of sodium dodecyl sulfate (SDS) in alkaline‐picrate reagent reduced the effect of bilirubin and protein for kinetic Jaffe method. Although adding potassium ferricyanide was well effective for eliminating negative interference of bilirubin, it was prone to interference from protein. Conclusions: Endogenous interferences continue to plague creatinine accuracy measurement in both Jaffe and enzymatic methods, and consequentially the estimated glomerular filtration rate. The addition of SDS to the alkaline‐pirate reagent was shown to be effective in reducing bilirubin and protein interferences. J. Clin. Lab. Anal. 24:123–133, 2010. © 2009 Wiley‐Liss, Inc.     

Evaluation of the IRMA TRUpoint and i-STAT creatinine assays

BACKGROUND: The i-STAT (Abbott Diagnostics, East Windsor, NJ) and IRMA TRUpoint (ITC, Edison, NJ) POCT analyzers were evaluated in an oncology center. METHODS: Precision and agreement with our core laboratory creatinine was judged by comparison of 50 consecutive chemotherapy patient results against the Roche rate-blanked Jaffe and enzymatic creatinine methods. Glomerular filtration rate (GFR) was estimated using the Cockroft-Gault (CG) calculation and Modification of Diet in Renal Disease Study (MDRD) equation. RESULTS: Precision varied from 1% (enzymatic)-6.1% (TRUpoint). Correlation was good (r>0.9948) with slopes within 5% of the Jaffe and enzymatic methods. Intercepts were <15.9 micromol/l (<0.18 mg/dl), and statistically significant bias (p<0.0025) was noted between the mean of patient specimens for i-STAT correlations to both the Jaffe and enzymatic laboratory creatinine methods. There was statistically significant concordance of estimated GFR between all methods, however, the agreement of estimated GFR to either the Jaffe or enzymatic creatinine laboratory methods was better for the TRUpoint (by either MDRD or CG estimation) and i-STAT (by MDRD equation) (Kappa>0.60) than the i-STAT (by CG estimation) (Kappa=0.41-0.60). CONCLUSION: Small biases in the calibration of analytical creatinine methods can lead to differences in clinical concordance using estimated GFR. Selecting an optimal POCT method depends on the institution's current creatinine method and tolerance for analytical performance and clinical concordance.     

酶法和Jaffe速率法测定血清肌酐的方法学比较

目的：了解酶法和Jaffe速率法测定血清肌酐结果的偏倚大小，为室间评估结果分组提供依据。方法：按照美国全国临床实验标准委员会（NCCLS）EP9－A文件进行评估，将测得的数据进行相关回归分析。计算两方法间的偏倚。结果．；酶法和Jaffe速率法测定肌酐，其回归方程式Y＝1．005X＋17．9（Y为Jaffe速率法，X为酶法），相关系数r=0.998，有明显恒定偏倚。结论：必须对不同方法原理的肌酐室间评估结果作分组处理。     

Variation of serum creatinine, cystatin C, and creatinine clearance tests in persons with normal renal function

BACKGROUND: To determine the potential sensitivity of several renal function tests for detecting early changes in renal function, we compared the within-individual (W-I) variation over 5 months of serum creatinine, serum cystatin C, and creatinine clearance. METHODS: On 31 healthy subjects, blood and timed urine specimens were collected once each month to get 6 collections. Creatinine (enzymatic) in serum and urine and cystatin C (immunonephelometric) in serum were measured and glomerular filtration rate (GFR) by creatinine clearance and the Modification of Diet in Renal Disease (MDRD) equation were calculated. To compare W-I variations between different creatinine methods, we also measured creatinine by both enzymatic and kinetic alkaline picrate methods on 15 sets of frozen samples. RESULTS: For the 31 volunteers, the mean W-I variations for serum creatinine (5.8%) and cystatin C (5.4%) were both much lower than the W-I variation of creatinine clearance (18.7%). As expected, the MDRD GFR had a similar W-I variation (6.7%) to that of serum creatinine and its values were markedly different than GFR by creatinine clearance. On the 15 sets of frozen samples, the W-I variation of creatinine measured by the enzymatic method (CV 5.2%) was slightly less than by the picrate method (CV 6.2%). CONCLUSIONS: The low W-I variation of both serum cystatin C and serum creatinine suggests that serial measurements of either would detect a changes in renal function earlier than would GFR by creatinine clearance or MDRD equation, which allows reporting only for GFRs<60 ml/min/1.7 m(2). While we measured only creatinine clearance, the large variability, difficulty, and cost of all clearance measurements make them impractical for routine monitoring of patients.     

酶法与碱性苦味酸法测定肌酐清除值的差异情况研究

目的研究酶法和碱性苦味酸法测定肌酐清除值（CrCl）的差异,探讨酶法CrCl采用国外参考区间是否合适。方法分别用肌氨酸氧化酶法（简称酶法）和碱性苦味酸速率法（简称苦味酸法）测定266名患者的血肌酐、尿肌酐以及CrCl,并以苦味酸法CrCl水平分为4组,第1-4组CrCl分别为〈25、26-50、51-80和〉81 mL/min。分析两法测定血肌酐、尿肌酐和CrCl结果的差异以及各组两法差异的变化。结果酶法血肌酐值和尿肌酐值低于苦味酸法（P〈0.001）,酶法CrCl除第1组外均高于苦味酸法（P〈0.001）。第1组两法血肌酐相对差值较小,且与两法尿肌酐相对差值接近,使CrCl在两法间无差异;第2-4组血肌酐相对差值逐渐增大,尿肌酐相对差值基本不变,导致CrCl在两法间出现差异且差异越来越大（P〈0.001）。结论CrCl〈25 mL/min时,两法CrCl没有差异;CrCl〉26 mL/min时,两法CrCl出现差异且差值逐渐增大;CrCl正常组两法差值很大,酶法CrCl采用国外参考区间不合适。     

Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values

PURPOSE: We sought to reexpress the 4-variable Modification of Diet in Renal Disease (MDRD) Study equation for estimation of glomerular filtration rate (GFR) using serum creatinine (S(cr)) standardized to reference methods. METHODS: Serum specimens included creatinine reference materials prepared by the College of American Pathologists (CAP), traceable to primary reference material at the NIST, with assigned values traceable to isotope dilution mass spectrometry (IDMS), a calibration panel prepared by the Cleveland Clinic Research Laboratory (CCRL), and frozen samples from the MDRD Study. Split specimens were measured at the CCRL using the Roche enzymatic and Beckman CX3 kinetic alkaline picrate assays. RESULTS: Roche enzymatic assay results on CAP samples were comparable to IDMS-assigned values. Beckman CX3 assay results in 2004-2005 were significantly higher than but highly correlated with simultaneous Roche enzymatic assay results (r(2) = 0.9994 on 40 CCRL samples) and showed minimal but significant upward drift from Beckman CX3 assay results during the MDRD Study in 1989-1991 (r(2) = 0.9987 in 253 samples). Combining these factors, standardized S(cr) = 0.95 x original MDRD Study S(cr). The reexpressed 4-variable MDRD Study equation for S(cr) (mg/dL) is GFR = 175 x standardized S(cr)(-1.154) x age(-0.203) x 1.212 (if black) x 0.742 (if female), and for S(cr) (micromol/L) is GFR = 30849 x standardized S(cr)(-1.154) x age(-0.203) x 1.212 (if black) x 0.742 (if female) [GFR in mL x min(-1) x (1.73 m(2))(-1)]. CONCLUSION: When the calibration of S(cr) methods is traceable to the S(cr) reference system, GFR should be estimated using the MDRD Study equation that has been reexpressed for standardized S(cr).     

血清肌酐两种测定方法偏倚的比较

目的分析肌氨酸氧化酶法（简称酶法）和苦味酸速率法（Jaffe′s法）测定血清肌酐结果的偏倚。方法依据美国国家临床实验室标准协会EP9-A文件,每天取临床样本8份,分别用两种方法测定血清Cre含量,共测定5d,记录结果,去除离群点,计算线性回归方程和相关系数,进行偏倚估计。结果在测定患者新鲜血清样本Cre时,酶法和Jaffe′s法测定结果的预期相对偏倚在Cre浓度小于100μmol/L时,两种方法的预期偏倚不超过-1.5%,酶法的测定结果低于Jaffe′s法;当Cre浓度大于300μmol/L时,两种方法的预期偏倚不低于6.4%,酶法的测定结果高于Jaffe′s法;当Cre浓度大于500μmol/L时,两种方法的预期偏倚不低于7.9%。结论预期偏倚在中低浓度时随肌酐浓度增高而降低,高浓度时则随浓度增高而增大,但Jaffe′s法测定结果较酶法低。临床实验室在换用不同仪器或试剂时必须对肌酐测定的不同方法建立不同的参考值范围。     

苦味酸法和酶法检测肌酐对肾小球滤过率预测公式效能的影响

目的 探讨应用苦味酸法和酶法检测肌酐对GFR评估方程适用性的影响.方法 选取2007-2009年华北(北京)、东北(大连)、华东(上海)、华中(长沙)4个区域三级甲等综合医院CKD患者176例.以双血浆法99m Tc-二乙三胺五乙酸(99mTc-DTPA)血浆清除率作为176例CKD患者的rGFR.使用4个不同厂家的酶法或苦味酸法肌酐试剂配套不同厂家自动生化分析仪分别测定患者血肌酐,同时应用体表面积( BSA)标化的Cockcroft-Gault方程(CG/BSA方程)、简化MDRD方程、校正至同位素稀释质谱法的简化MDRD方程(MDRD-IDMS方程)、CKD流行病学合作研究方程(CKD-EPI方程)及2个国内简化MDRD改良方程(课题组方程1、2)分别计算eGFR,比较不同估算结果与rGFR的相关性、偏差、精密度以及30％准确性.结果 176例CKD患者的rGFR为[40.70(19.41～84.35)] ml·min-1·(1.73 m2)-1.应用苦味酸法测定肌酐时,各方程评估的eGFR与rGFR的ICC在0.879～0.923之间;应用酶法测定肌酐时,各方程评估的eGFR与rGFR的ICC在0.925 ～0.946之间,相关性优于应用苦味酸法测定肌酐.Bland-Altman图显示,各方程评估的eGFR在高值区偏差较大,但用酶法时偏离程度均小于应用苦味酸法.在rGFR≥60 ml·min-1·(1.73 m2)-1时,各方程应用酶法测定肌酐时的30％准确性在68.3％～90.0％之间,应用苦味酸法30％准确性在41％～75％之间,除课题组方程1外,其他方程应用酶法测定肌酐时的准确性均显著高于苦味酸法.而rGFR＜60ml· min-1·(1.73 m2)-1时,应用酶法、苦味酸法测定肌酐的30％准确性分别在39.7％～49.1％、40.5％～52.6％之间.对于同一方程,应用酶法测定肌酐的两套不同检测系统间,其30％准确性差异无统计学意义,而应用苦味酸法的两套不同检测系统间,其30％准确性差异有统计学意义.结论 同一评估方程使用苦味酸法和酶法两种不同的肌酐检测方法时,结果存在显著性差异.采用酶法测定肌酐时,方程评估的eGFR结果在相关性、偏离程度、准确性方面均优于苦味酸法.     

Beta-trace protein, cystatin C, beta(2)-microglobulin, and creatinine compared for detecting impaired glomerular filtration rates in children

BACKGROUND: Because of the limitations of serum creatinine as a marker of glomerular filtration rate (GFR) in children, we assessed the diagnostic accuracy of the novel marker beta-trace protein (BTP) in comparison with cystatin C (Cys-C), beta(2)-microglobulin (beta(2)-MG), and creatinine as conventional indicators of reduced GFR. METHODS: We obtained serum samples from 225 children (age range, 0.2-18 years) with various renal pathologies who were referred for nuclear medicine clearance investigations (technetium-diethylenetriamine pentaacetic acid or chromium-EDTA). We measured Cys-C, BTP (nephelometric tests; Dade Behring), beta(2)-MG (Tinaquant; Roche), and creatinine (enzymatic assay; Creatinine-PAP; Roche). RESULTS: Seventy-five children had reduced GFR (<90 mL x min(-1) x 1.73 m(-2)). One hundred fifty children (independent of gender and age) with values >90 mL x min(-1) x 1.73 m(-2) comprised the control group with gaussian distributions of BTP and Cys-C concentrations. The upper reference limits (97.5 percentile) were 1.01 mg/L for BTP and 1.20 mg/L for Cys-C. The correlations of nuclear medicine clearance with the reciprocals of BTP, Cys-C, and the Schwartz GFR estimate were significantly higher (r = 0.653, 0.765, and 0.706, respectively; P <0.05) than with the reciprocal of creatinine or beta(2)-MG (r = 0.500 and 0.557, respectively). ROC analysis showed a significantly higher diagnostic accuracy of BTP, Cys-C, and the GFR estimate for the detection of impaired GFR than serum creatinine (P <0.05). Compared to creatinine, BTP increased the diagnostic sensitivity by approximately 30%, but it was not more sensitive than Cys-C or the Schwartz GFR estimate. CONCLUSIONS: BTP is superior to serum creatinine and an alternative for Cys-C to detect mildly reduced GFR in children, but it is not better than the Schwartz GFR estimate.     

酶法与碱性苦味酸法测定肌酐清除值的差异情况研究

目的研究酶法和碱性苦味酸法测定肌酐清除值(CrCl)的差异,探讨酶法CrCl采用国外参考区间是否合适。方法分别用肌氨酸氧化酶法(简称酶法)和碱性苦味酸速率法(简称苦味酸法)测定266名患者的血肌酐、尿肌酐以及CrCl,并以苦味酸法CrCl水平分为4组,第1~4组CrCl分别为<25、26~50、51~80和>81 mL/min。分析两法测定血肌酐、尿肌酐和CrCl结果的差异以及各组两法差异的变化。结果酶法血肌酐值和尿肌酐值低于苦味酸法(P<0.001),酶法CrCl除第1组外均高于苦味酸法(P<0.001)。第1组两法血肌酐相对差值较小,且与两法尿肌酐相对差值接近,使CrCl在两法间无差异;第2~4组血肌酐相对差值逐渐增大,尿肌酐相对差值基本不变,导致CrCl在两法间出现差异且差异越来越大(P<0.001)。结论CrCl<25 mL/min时,两法CrCl没有差异;CrCl>26 mL/min时,两法CrCl出现差异且差值逐渐增大;CrCl正常组两法差值很大,酶法CrCl采用国外参考区间不合适。     

血清肌酐测定基质效应的研究

目的 评价血清肌酐测定常规方法的校准偏差及肌酐制备物常在常规方法上的基质效应.方法 根据美国临床实验室和标准化协会(CLSI)EP14-A2评价方案,同位素稀释液相色谱串联质谱法(ID-LC/MS/MS)测定血清肌酐的方法为比对方法,15种常规肌酐测定系统(7种酶法,8种苦味酸法)为待评方法,测定40个新鲜冰冻人血清和36种制备物的肌酐浓度,评价制备物的基质效应和测定系统的校准偏差.结果 大部分商品制备物(29/30)在苦味酸法系统上表现出基质效应,少部分商品制备物(13/30)在部分酶法系统上表现出基质效应.我中心6个制备物在所有15个系统上均未观察到基质效应.所有常规系统新鲜冰冻血清测定值与比对方法测定值间均呈较好的直线相关,所有苦味酸法和部分酶法测定肌酐方法存在校准偏差.结论 基质效应和校准偏差存在于常规肌酐测定方法,必须重视这些因素,提高肌酐测定结果的正确度和可比性.     

Impact of serum creatinine measurement error on dose adjustment in renal failure

BACKGROUND: Doses of renally eliminated drugs should be adjusted according to kidney function to prevent adverse drug events and cost. Dose adjustment can be based on serum creatinine level, subsequent creatinine clearance estimation, and dosage calculation with consideration of the renal elimination properties of the respective compound. OBJECTIVE: Our objective was to quantify the impact and relevance of serum creatinine measurement error on dose adjustment in renal failure. METHODS: We analyzed 27914 measurements from external quality assessment surveys of 1878 German laboratories that used a kinetic alkaline picrate (69% of results) or an enzymatic method (25%) for creatinine determination. Linear models were fit for both methods combined and separately. On the basis of 95% confidence intervals (CIs) for creatinine values, 95% CIs for drug dosing were calculated. RESULTS: The 95% CI for a measured serum creatinine value was 0.80. Measured value < Reference method value < 1.28. Measured value for the kinetic alkaline picrate method and 0.87. Measured value < Reference method value < 1.21. Measured value for the enzymatic method. Applied to a data set of 6.5 million simulated patients with all possible combinations of characteristics relevant for drug dosing, the dosing error caused by serum creatinine measurement error did not exceed 25% in patients with creatinine clearance estimates lower than 50 mL/min according to the Cockcroft-Gault equation. For drugs completely eliminated by the kidneys in active form, the dosing error was up to 6-fold smaller than that which would occur if doses were not adjusted. CONCLUSION: The serum creatinine measurement error of current laboratory methods is small and is comparable to other errors influencing dose adjustment.     

Lactulose interferes in the alkaline picrate assay for creatinine

Errors of more than 10 mg/L in measured serum creatinine concentrations were encountered for an azotemic patient who was given lactulose orally. The magnitude of the apparent error fluctuated with the dose of lactulose. Additions of lactulose to serum produced a linear increase in the creatinine measured by each of two automated methods that involve use of the alkaline picrate (Jaffé) reaction. A lactulose concentration of 100 g/L produced positive interferences of 30 and 65 mg/L in kinetic (Beckman Astra) and continuous-flow (Technicon SMAC) assays, respectively, but caused no problem in an enzymatic assay for creatinine. The results of creatinine assays must be interpreted with caution in patients treated with lactulose.     

Deproteinization of serum: another best approach to eliminate all forms of bilirubin interference on serum creatinine by the kinetic Jaffe reaction

The negative interference of conjugated, unconjugated, and delta bilirubin on patient serum creatinine determined by the kinetic Jaffe reaction is the unresolved problem. We compared bilirubin interference on thirty patients' serum creatinine obtained from four analyzers, with and without deprotenization before the Jaffe reaction, to the Vitros dry enzymatic method. We found significant negative interference from bilirubin on serum creatinine in all samples directly applied to four wet chemical methods, except the one incorporated with serum blank rate. The negative interferences linearly related to bilirubin concentration. However, bilirubin did not interfere on serum creatinine obtained from all wet chemical methods incorporated with deproteinization process before the reaction. We conclude that deproteinized serum before the reaction is the best approach to eliminate all forms of bilirubin interference on serum creatinine determined by the kinetic Jaffe reaction.     

Enzymatic assays for creatinine: time for action.

Accurate serum creatinine measurements in glomerular filtration rate estimation (eGFR) using equations are critical to ongoing global public health efforts to improve the diagnosis and treatment of chronic kidney disease. There is now an ongoing activity to promote worldwide standardization of methods to determine creatinine together with the introduction of a revised eGFR equation appropriate for use with standardized creatinine methods. Standardization of calibration, i.e., implementation of calibration traceability to high-order reference measurement procedures and reference materials, does not, however, correct for analytical interferences of field methods (non-specificity bias). To account for the sensitivity of alkaline picrate-based methods to non-creatinine chromogens, some manufacturers have adjusted the calibration to minimize the pseudo-creatinine contribution of plasma proteins, producing results more closely aligned to the reference method (isotope dilution-mass spectrometry), but this strategy makes an assumption that the non-creatinine chromogen interference is a constant among samples, which is an oversimplification. Thus, analytical non-specificity for substances found in individual patient samples can affect the accuracy of eGFR computed from serum creatinine values for any alkaline picrate method, including the so-called "compensated" Jaffé methods. The use of assays that are more specific for serum creatinine determination, such as those based on enzymatic reactions, may provide more reliable eGFR values. Supporting the choice of more specific assays by clinical laboratories represents one of the main tasks of our profession in order to achieve the ultimate clinical goal, which is to routinely report an accurate eGFR in all the pertinent clinical situations.     

Impact of standardized calibration on the inter-assay variation of 14 automated assays for the measurement of creatinine in human serum.

PURPOSE: The aim of our study was to measure the inter-assay variation and accuracy of serum creatinine assays and to assess the effect of standardized calibration procedures on this variability. METHODS: We analyzed 30 human sera and three reference materials, using 17 creatinine assays (12 colorimetric, 4 enzymatic and 1 HPLC). We compared two standardized calibration procedures, using either a reference material or secondary standards, to that recommended by the manufacturers. RESULTS: For assays calibrated according to the manufacturers' recommendations, the median inter-assay coefficient of variation (CV) was 14.2% for 20 low samples (45-150 microM), and 7.7% for 10 high samples (250-350 microM). The CV was significantly influenced by the calibration procedure, but none of the standardized calibration procedures significantly improved the inter-assay variability. However, a significant decrease in CV was noted within each type of assay method (colorimetric or enzymatic) when the standardized calibration used standards of level(s) close to the concentrations to be measured. Only the compensated Jaffe technique and the amido-hydrolase assay showed bias of less than 10%. CONCLUSIONS: Standardizing calibration procedures is unlikely to decrease the analytical variability of creatinine assays enough to allow uniform and reliable use of the equations for estimation of glomerular filtration rate.     

Evaluation of renal function in intensive care: plasma cystatin C vs. creatinine and derived glomerular filtration rate estimates.

Plasma cystatin C, a new marker of glomerular filtration rate (GFR), was prospectively evaluated in surgical intensive care. Cystatin C was measured (immunonephelometry, Dade-Behring) in 10 patients selected to cover a full range of GFR (phase I) and in 28 unselected consecutive patients followed for 5 days post-admission (phase II). Results were compared with (51)Cr-EDTA clearance (phase I only), plasma creatinine (kinetic Jaffe, Roche), 24-h or estimated by Cockcroft and Gault (CG) creatinine clearance (CrCl), and modified diet in renal disease (MDRD)-estimated GFR. In phase I, the highest correlation with(51)Cr-EDTA clearance (22-198 mL/min) was noted for CG CrCl (r(2): 0.883, p<0.001). During phase II follow-up, 24-h CrCl could not be calculated in 25% of daily evaluations. Cystatin C correlated with creatinine (0.856, p<0.0001) and CG CrCl with MDRD GFR (0.926, p<0.0001) in renal failure (10-78 mL/min, n=60). There was a +40% (p<0.001) median difference between cystatin C and creatinine (as a % of upper normal cut-off). Sensitivity/specificity to detect a <80 mL/min CG CrCl was 88/97% for cystatin C vs. 48/100% for creatinine (laboratory cut-off). In patients with normal and stable renal function (n=14), day-to-day intra-individual variation was 7.4% for cystatin C (vs. 10.6% for creatinine). In intensive care unit surgical adult patients, CG CrCl provides an easy and cost-effective estimate of GFR. Superior to creatinine, plasma cystatin C can be measured in selected patients where CG CrCl is known to be inaccurate.     

利用Rate-Blank消除胆红素对肌酐测定的负干扰因素

目的分析苦味酸法测定肌酐时胆红素干扰物质的影响,探讨一种消除胆红素干扰苦味酸法测定肌酐的方法。方法在日立7170A全自动生化分析仪上设定两种苦味酸测量肌酐的方法,一种为RateA,另一种利用带血清信息的空白速率(Rate-Blank)RateA法,参数设定为测定方法RateA,反应时间10分钟,读数点〔19 23 11 15〕。用两种方法分别测定正常体检组、高胆红素组标本血清肌酐的浓度。将以上两种方法测得的结果与酶法测得的结果进行对比分析。结果高胆红素对Rat-eA法测量肌酐有明显负干扰,采用Rate-Blank RateA法后此干扰明显降低。结论采用Rate-Blank RateA可基本消除胆红素对苦味酸测定肌酐的干扰。     

Standardization of p-creatinine assays and use of lean body mass allow improved prediction of calculated glomerular filtration rate in adults: a new equation

OBJECTIVE: To evaluate the Cockcroft-Gault (CG) equation, using various body weight expressions, and the Sawyer equation in predicting glomerular filtration rate (GFR) using an enzymatic and zero-calibrated Jaffe plasma-creatinine assay, and to derive a new robust equation in adults. MATERIAL AND METHODS: The CG weight measures included total, ideal and adjusted body weight (ABW; lowest of total and ideal) and two lean body mass (LBM) expressions, while the Sawyer equation is based primarily on LBM. Iohexol clearance was used to measure GFR. One derivation set (n = 436; enzymatic assay) was used to evaluate and bias-adjust existing equations when indicated, and to derive a new equation based on plasma-creatinine, age, gender and the body weight measure yielding the best adjusted R2. All equations were then validated in a separate set (n = 414; Jaffe assay). RESULTS: The existing equations all performed similarly in both sets. Prediction errors of equations based on LBM showed no correlation with BMI. The CGABW and Sawyer equations performed best. The new equation with LBM yielded the highest adjusted R2. In the combined set (n = 850), its accuracy (86 %/98 % of estimates within 30 %/50 % of measured GFR) was significantly better than for the CGABW (79 %/95 %) and Sawyer equations (79 %/93 %) (p<0.001) for each 30 mL/min GFR subgroup within +/-30 % and +/-50 %, except within +/-30 % >120 mL/min. Prediction error did not correlate with BMI, age or gender. CONCLUSION: A new creatinine-based equation derived in a mainly Caucasian patient sample is a better predictor of GFR than CG-type equations irrespective of the body weight measure used or, if bias-adjusted, when using zero-calibrated creatinine assays.     

血清胱抑素C：一种简便测定肾小球滤过率的标志物

目的 :评价测定肾小球滤过率 (GFR)的一种简便方法—血清胱抑素C检测的临床意义。方法 :对 5 0例不同肾病患者及70名正常人同时测定血清胱抑素C及内生肌酐清除率、血肌酐值 ,并对两组结果进行相关分析。结果 :血清胱抑素C与内生肌酐清除率及血肌酐值有高度相关性 (r值分别为r =- 0 .83 4 ,p <0 .0 0 1和r =0 .867,p <0 .0 0 1)。结论 :血清胱抑素C检测是一种简便、可靠测定GFR的标志物