Comparison of Direct and Extraction Immunoassay Methods With Liquid Chromatography-Tandem Mass Spectrometry Measurement of Urinary Free Cortisol for the Diagnosis of Cushing’s Syndrome

Background@#Twenty-four-hour urinary free cortisol (UFC) measurement is the initial diagnostic test for Cushing’s syndrome (CS). We compared UFC determination by both direct and extraction immunoassays using Abbott Architect, Siemens Atellica Solution, and Beckman DxI800 with liquid chromatography-tandem mass spectrometry (LC-MS/MS). In addition, we evaluated the value of 24-hr UFC measured by six methods for diagnosing CS. @*Methods@#Residual 24-hr urine samples of 94 CS and 246 non-CS patients were collected.A laboratory-developed LC-MS/MS method was used as reference. UFC was measured by direct assays (D) using Abbott, Siemens, and Beckman platforms and by extraction assays (E) using Siemens and Beckman platforms. Method was compared using Passing–Bablok regression and Bland–Altman plot analyses. Cut-off values for the six assays and corresponding sensitivities and specificities were calculated by ROC analysis. @*Results@#Abbott-D, Beckman-E, Siemens-E, and Siemens-D showed strong correlations with LC-MS/MS (Spearman coefficient r = 0.965, 0.922, 0.922, and 0.897, respectively), while Beckman-D showed weaker correlation (r = 0.755). All immunoassays showed proportionally positive bias. The areas under the curve were 0.975 for Abbott-D, 0.972 for LCMS/MS, 0.966 for Siemens-E, 0.948 for Siemens-D, 0.955 for Beckman-E, and 0.877 for Beckman-D. The cut-off values varied significantly (154.8–1,321.5 nmol/24 hrs). Assay sensitivity and specificity ranged from 76.1% to 93.2% and from 93.0% to 97.1%, respectively. @*Conclusions@#Commercially available immunoassays for measuring UFC show different levels of analytical consistency compared to LC-MS/MS. Abbott-D, Siemens-E, and Beckman-E have high diagnostic accuracy for CS.

Influencing factors and interpretation of the clinical laboratory assay result of acute kidney injury / 中华检验医学杂志

[Abstrct] More and more laboratory indicators including serum creatinine , serum cystatin C , urinary microalbumin, N-acetyl-beta-D-Glucosaminidase (NAG), kidney injury molecule 1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), interleukin 18 (IL-18) and L type fatty acid binding protein (L-FABP) are used to diagnose and monitor acute kidney injury (AKI).However, the clinical applicability and limitations of these indicators , as well as the detection effect factors and biological variation on the diagnosis and monitoring of AKI are very important , especially how to combine the detection effect factors and biological variation to interpret test result is attached great importance by the laboratory personnel .

Negative interference by calcium dobesilate in uricase-peroxidase coupled assays of serum uric acid / 中华检验医学杂志

Objective To assess the interference by calcium dobesilatein 7 peroxidase-baseduric acid assays and to determine its clinical significance.Methods In the in vitro experiments, uric acid in pooled serum with final concentrations of calcium dobesilate additions (0, 2, 4, 8, 16, 32, and 64μg/ml) were measured by 7 peroxidase-based assays.Percent Bias (%) was calculated relative to the drug-free specimen.In the in vivo experiments, changes in serum uric acid and calcium dobesilate concentrations were observed before and after calcium dobesilate administration ( baseline, 0 h, 1 h, 2 h, 3 h, 4 h, 6 h ) involunteers.The interference in different assays was assessed compared with LC-IDMS/MS method. Calcium dobesilate levels in 40 specimens from those taking calcium dobesilate were measured by HPLC method.Of the 40 specimens, 10 were selected to analyse the levels of uric acid by both peroxidase and UV measurement method to assess the impact in clinical status.Results In the in vitro study, concentrations of uric acid measured by 7 peroxidase-based assays were reduced by -6.3%to -21.2%compared with drug-free serum, when theconcentration of calcium dobesilate was16μg/ml.In the in vivo study, comparedto UA levels at 0 h, the biasesof serum uric acid determined by peroxidase method after calcium dobesilate administration(1 h, 2 h, 3 h, 4 h, 6 h) were of -3.33%, -6.79%, -7.49%, -6.07%, -4.09%, respectively.The observed uric acid concentrations for 8 participants measured by enzymatic assays were inhibited by -3.75% to -6.89% at 0 hour and by -16.9% to-22.22% at 2 hours relative to the concentrations measured by the LC-IDMS/MS method. Conclusions Calcium dobesilate produced a clinically significant negative interference with uric acid in all peroxidase-based uric acid assays,which may result in false evaluation of uric acid level in clinical status.Significant differences in the degree of interference were observed among the assays.

Assessment of the consistency of five standardized cystatin C measurement systems / 中华检验医学杂志

Objective To assess the consistency of four standardized cystatin C particle-enhanced turbidimetric assay (PETIA) and one particle-enhanced nephelometric immunoassay (PENIA) measurement systems Methods Performance verification test was conducted according to CLSI EP 15-A2 and EP9-A2. Fourty serum samples in comparative test were obtained from the remaining serum samples of outpatients in Peking Union Medical College Hospital in March 2013.Fourty serum samples were tested on Olympus AU5400 automatic biochemical analyzer ( four PETIA Cys C reagents:Shanghai Jingyuan Co ., Ltd, Beijing Leadman Biochemistry Co ., Ltd, Beijing Strong Biotechnologies , Maker Biotechnology in Sichuan , and labelled as A, B, C, D respectively) and PENIA N Latex Cys C measurement system on Siemens BNⅡ(labelled as E).Correlation analysis were performed among four PETIA methods one PENIA method Differences of each detection system were compared in the medical decision level 1,2,3,4 mg/L.The reference material ERM-DA471/IFCC was measured by five systems and bias ( percentage bias ) was calculate for each system.Results Results of systems A, B, C, D, E were 1.29(0.89-2.43), 1.30 (0.96-2.59), 1.22(0.90-2.44), 1.27(0.96-2.47), 1.14(0.82-2.05)mg/L.Chart shows bias among these five systems was small when Cys C concentration was less than 4mg/L.PETIA method A, B, C, D correlated with their mean value well , with the average deviation from their mean value ( percent deviation) at -0.017 -0.031 mg/L ( -3.1%-2.1%), and all were less than allowed bias from the biological variation (3.4%).The deviation of PETIA method A, B, C, D with their mean value in medical decision level at -0.176 -0.178 mg/L.Systems A, B, C, D correlated well with the result of PENIA method system E , and the mean deviation ( percent deviation ) was at 0.278 -0.326 mg/L ( 12.6%-18.5%) , and the deviation ( percent deviation ) in the medical decision level 0.055 -1.079 mg/L (5.51%-26.98%).Bias of PETIA method A, B, C, D Cys C system measuringERM -DA471/IFCC ranged from 0.22 to 0.39 mg/L ( 3.9%-7.0%) , which exceeded the allowable range of the reference material target value, and were larger than the allowable bias from biological variation (3.4%).Bias ( percent ) of PENIA method system E was -0.1 mg/L ( -1.7%) , within the allowable range of ERM-DA471/IFCC target value .Conclusions The consistency of four assesed PETIA Cys C reagents was relatively ideal, and improved markably after being traced to ERM-DA471/IFCC.Besides, the results of PETIA were higher than those of PENIA .Bias among these five systems was small when Cys C concentration was less than 4 mg/L, and the bias became larger in higher Cys C concentration.