The Roche Immunoturbidimetric Albumin Method on Cobas c 501 Gives Higher Values Than the Abbott and Roche BCP Methods When Analyzing Patient Plasma Samples.

BACKGROUND: Serum/plasma albumin is an important and widely used laboratory marker and it is important that we measure albumin correctly without bias. We had indications that the immunoturbidimetric method on Cobas c 501 and the bromocresol purple (BCP) method on Architect 16000 differed, so we decided to study these methods more closely. METHOD: A total of 1,951 patient requests with albumin measured with both the Architect BCP and Cobas immunoturbidimetric methods were extracted from the laboratory system. A comparison with fresh plasma samples was also performed that included immunoturbidimetric and BCP methods on Cobas c 501 and analysis of the international protein calibrator ERM-DA470k/IFCC. RESULTS: The median difference between the Abbott BCP and Roche immunoturbidimetric methods was 3.3 g/l and the Roche method overestimated ERM-DA470k/IFCC by 2.2 g/l. The Roche immunoturbidimetric method gave higher values than the Roche BCP method: y = 1.111x - 0.739, R² = 0.971. CONCLUSION: The Roche immunoturbidimetric albumin method gives clearly higher values than the Abbott and Roche BCP methods when analyzing fresh patient samples. The differences between the two methods were similar at normal and low albumin levels.

Accuracy of GFR estimating equations combining standardized cystatin C and creatinine assays: a cross-sectional study in Sweden.

BACKGROUND: The recently established international cystatin C calibrator makes it possible to develop non-laboratory specific glomerular filtration rate (GFR) estimating (eGFR) equations. This study compares the performance of the arithmetic mean of the revised Lund-Malmö creatinine and CAPA cystatin C equations (MEANLM-REV+CAPA), the arithmetic mean of the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI) creatinine and cystatin C equations (MEANCKD-EPI), and the composite CKD-EPI equation (CKD-EPICREA+CYSC) with the corresponding single marker equations using internationally standardized calibrators for both cystatin C and creatinine. METHODS: The study included 1200 examinations in 1112 adult Swedish patients referred for measurement of GFR (mGFR) 2008-2010 by plasma clearance of iohexol (median 51 mL/min/1.73 m2). Bias, precision (interquartile range, IQR) and accuracy (percentage of estimates ±30% of mGFR; P30) were compared. RESULTS: Combined marker equations were unbiased and had higher precision and accuracy than single marker equations. Overall results of MEANLM-REV+CAPA/MEANCKD-EPI/CKD-EPICREA+CYSC were: median bias -2.2%/-0.5%/-1.6%, IQR 9.2/9.2/8.8 mL/min/1.73 m2, and P30 91.3%/91.0%/91.1%. The P30 figures were about 7-14 percentage points higher than the single marker equations. The combined equations also had a more stable performance across mGFR, age and BMI intervals, generally with P30 ≥90% and never <80%. Combined equations reached P30 of 95% when the difference between eGFRCREA and eGFRCYSC was <10% but decreased to 82% at a difference of ≥40%. CONCLUSIONS: Combining cystatin C and creatinine assays improves GFR estimations with P30 ≥90% in adults. Reporting estimates of both single and combined marker equations in clinical settings makes it possible to assess the validity of the combined equation based on the agreement between the single marker equations.

Generation of a new cystatin C-based estimating equation for glomerular filtration rate by use of 7 assays standardized to the international calibrator.

BACKGROUND: Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays. METHODS: Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR. RESULTS: We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C. CONCLUSIONS: A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.

The revised Lund-Malmö GFR estimating equation outperforms MDRD and CKD-EPI across GFR, age and BMI intervals in a large Swedish population.

BACKGROUND: The performance of creatinine-based glomerular filtration rate (GFR) estimating equations may vary in subgroups defined by GFR, age and body mass index (BMI). This study compares the performance of the Modification of Diet in Renal Disease (MDRD) study and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations with the revised Lund-Malmö equation (LM Revised), a new equation that can be expected to handle changes in GFR across the life span more accurately. METHODS: The study included 3495 examinations in 2847 adult Swedish patients referred for measurement of GFR (mGFR) 2008-2010 by plasma clearance of iohexol (median 52 mL/min/1.73 m²). Bias, precision [interquartile range (IQR)] and accuracy [percentage of estimates ±10% (P10) and ±30% (P30) of mGFR] were compared. RESULTS: The overall results of LM Revised/MDRD/CKD-EPI were: median bias 2%/8%/11%, IQR 12/14/14 mL/min/1.73 m², P10 40%/35%/35% and P30 84%/75%/76%. LM Revised was the most stable equation in terms of bias, precision and accuracy across mGFR, age and BMI intervals irrespective of gender. MDRD and CKD-EPI overestimated mGFR in patients with decreased kidney function, young adults and elderly. All three equations overestimated mGFR and had low accuracy in patients with BMI <20 kg/m², most pronounced among men. CONCLUSIONS: In settings similar to the investigated cohort LM Revised should be preferred to MDRD and CKD-EPI due to its higher accuracy and more stable performance across GFR, age and BMI intervals.

Measurement of urinary cystatin C with a particle-enhanced turbidimetric immunoassay on Architect ci8200.

BACKGROUND: Cystatin C is a low-molecular-weight protein that is freely filtered by the glomerulus and catabolized after reabsorption by the proximal tubular cells in healthy subjects. Urinary cystatin C is a potential biomarker for tubular damage including acute kidney injury (AKI) in the acute phase when patients are submitted to the intensive care unit. METHODS: The aim of this study was to perform a method validation of urinary analysis of cystatin C by particle-enhanced turbidimetric immunoassay (PETIA) on a high-throughput chemical analyzer. Total assay time was 10 min. The antigen excess, linearity, lower limit of quantification (LoQ), recovery, assay precision, stability, and interference caused by hemoglobin were evaluated. RESULTS: The LoQ was calculated to 0.020 mg/l with a coefficient of variation (CV) ≤ 10%. No hook effect was observed and the assay was linear over the studied interval less than 0.020-0.950 mg/l with a regression of R² = 0.9994. The assay had a recovery between 93-100% and the assay precision had a total CV of less than 3.5%. Cystatin C was stable for 3 days in room temperature and 14 days in +4C. The assay did not show any major interference with hemoglobin at a hemoglobin concentration of 10 g/L. The reference interval for urine cystatin C was less than 0.166 mg/l. CONCLUSION: The urinary cystatin C PETIA showed good precision and performance characteristics including short test turnaround times that are necessary qualifications for a biomarker at a routine laboratory.

Early and late outcome prediction of death in the emergency room setting by point-of-care and laboratory assays of cardiac troponin I.

BACKGROUND: Point-of-care (POC) assays of cardiac troponins are common in the emergency department setting. The question raised was as follows: What is the clinical impact of the results of POC assays of cardiac troponins as compared with sensitive laboratory assays? METHODS: Patients admitted consecutively to the emergency department (N = 1,069) and on whom cardiac troponins were requested as part of their clinical work-up were included. Cardiac troponin I (cTnI) was measured by the POC assays-i-Stat (Abbott Diagnostics, Abbott Park, IL) and Stratus CS (Siemens Healthcare Diagnostics, Deerfield, IL)-and by the laboratory assays-Access AccuTnI (Beckman Coulter, Fullerton, CA) and Architect cTnI (Abbott Diagnostics). Results were related to early (14 days) and late outcome (median 3.3 months, range 0.1-35) as to death. RESULTS: The laboratory assays identified more patients (P < .001) with elevated levels than the two POC assays (39%-74% vs 20%-27%). Adopting the 99th percentiles upper reference limit, the Access AccuTnI identified 88% and Architect cTnI identified 81% of all patients who died of cardiovascular disease as compared with 50% and 54% for i-Stat and Stratus CS, respectively (P < .001). Negative predictive values for the laboratory assays were 97% as compared with 89% to 93% for the POC assays. Negative likelihood ratios were 0.25 (CI 0.15-0.041) and 0.59 to 0.68 (CI 0.47-0.79), respectively. CONCLUSIONS: The current POC cTnI assays are less sensitive for outcome prediction of patients with myocardial injury. The clinical judgment of the patient with suspected myocardial ischemia should not solely rely on results from POC assays. If a clinical suspicion of myocardial injury remains despite negative cTnI results with the POC assays, such results should be complemented by results from sensitive laboratory assays.

Performance evaluation of a turbidimetric cystatin C assay on different high-throughput platforms.

OBJECTIVE: The goal with this study was to evaluate the analytical performance of a new cystatin C immunoassay (Tina-quant a Cystatin C, Roche Diagnostics GmbH). The evaluation was carried out at four centers according to a standardized protocol. MATERIAL AND METHODS: The Tina-quant a Cystatin C is a latex particle-enhanced immunoturbidimetric assay. Roche cobas 6000, MODULAR ANALYTICS SWA and COBAS INTEGRA instruments were included in the study. Method comparison studies were carried out against two turbidimetric methods (Dako Cystatin C, Gentian Cystatin C), and one nephelometric method (Siemens N-Latex Cystatin C). RESULTS: Linearity was proven throughout the measuring range from 0.4 to 8 mg/L. Within-run CVs ranged from 0.7-2.8%, and total CVs from 1.4-4.7 % (concentration range 0.6-3.9 mg/L). Comparable results were obtained with paired serum and Li-heparinate plasma samples. Good agreement was achieved in the comparisons between the Tina-quant a Cystatin C assay and the other commercially available cystatin C assays, two different turbidimetric methods (slope range 0.88-1.04, intercept < 0.17 mg/L, r > or = 0.993) and one nephelometric assay (slope range 0.90-1.05, intercept < 0.21 mg/L, r > or = 0.986). CONCLUSIONS: The Tina-quant a Cystatin C assay was shown to be precise and accurate with proven linearity over the measuring range. Good comparability was obtained with other commercially available assays for the determination of cystatin C. The Tina-quant a Cystatin C assay is very well suited for clinical use on routine clinical chemistry analysers to detect renal dysfunction with a 24 h availability.

Evaluation of Dade Behring N Latex Cystatin C reagent on Abbott ci8200.

Plasma cystatin C has been shown in several studies to be superior to plasma creatinine for estimation of glomerular filtration rate (GFR). Reporting cystatin C results in mL/min using conversion formulas for transforming cystatin C expressed as mg/L to GFR expressed as mL/min has greatly facilitated the clinical use of the marker. At our hospital we have an increasing demand for cystatin C and at present we perform over 1400 cystatin C analyses a month. The test is available at all hours. This in combination with the volume emphasises the need to have the assay close to the routine chemistry instrument to reduce handling time per test and time to report test results. We have thus evaluated the Dade Behring N Latex Cystatin C assay (Dade Behring, Deerfield, IL, USA) on Architect ci8200 (Abbott Laboratories, Abbott Park, IL, USA). The nephelometric method on the ProSpec (Dade Behring) and the turbidimetric method on Architect ci8200 showed very good agreement (y = 1.0072x + 0.0042; R2 = 0.987). Accordingly, running the cystatin C analyses on a chemistry instrument (Architect ci8200) would be proper to increase the availability of the analysis and reduce turnaround times.

Comparison between Cystatin C- and Creatinine-Estimated Glomerular Filtration Rate in Cardiology Patients.

OBJECTIVE: Estimation of the glomerular filtration rate (GFR) is essential for identification, evaluation and risk prediction in patients with kidney disease. Estimated GFR (eGFR) is also needed for the correct dosing of drugs eliminated by the kidneys and to identify high-risk individuals in whom coronary angiography or other procedures may lead to kidney failure. Both cystatin C and creatinine are used for the determination of GFR, and we aimed to investigate if eGFR by the two methods differ in cardiology patients. METHODS: We compared cystatin C and creatinine (CKD-EPI) eGFR calculated from the same request from a cardiology outpatient unit (n = 2,716), a cardiology ward (n = 980), a coronary care unit (n = 1,464), and an advanced coronary care unit (n = 518) in an observational, cross-sectional study. RESULTS: The median creatinine eGFR results are approximately 10 ml/min/1.73 m(2) higher than the median cystatin C eGFR that is up to 90 ml/min/1.73 m(2), irrespective of the level of care. Creatinine eGFR resulted in a less advanced eGFR category in the majority of patients with a cystatin C eGFR <60 ml/min/1.73 m(2). CONCLUSIONS: Our study demonstrates a difference between creatinine and cystatin C eGFR in cardiology patients. It is important to be aware of which marker is used for the reported eGFR to minimize erroneous interpretations of the test results, as this could lead to under- or overmedication. Further studies are needed to determine the best method of estimating the GFR in cardiology units.

[Analysis of beta-"trace" protein detects leakage of cerebrospinal fluid. Quickly, safely and cheaply]. / Analys av beta-"trace"-protein spårar läckage av cerebrospinalvätska. Snabbt, säkert och billigt.

beta-trace protein is an immunological marker for the detection of cerebrospinal fluid leakage to the nose or ear. Analysis of beta-trace protein via a nephelometric assay is a valuable test for the identification of cerebrospinal fluid in rhinorrhea or otorrhea.

The age related association is more pronounced for cystatin C estimated GFR than for creatinine estimated GFR in primary care patients.

OBJECTIVES: There is an age associated change in GFR but this association may be influenced by the method used. The aims of the present study were to assess the association between age and cystatin C and creatinine based glomerular filtration rate estimates in primary care patients, and to determine the proportion of patients with clinically important renal impairment. MATERIALS AND METHODS: 1552 samples with simultaneous requests for creatinine and cystatin C from 1552 primary care patients in the county of Uppsala, Sweden were analysed. MDRD, CKD-EPI and cystatin C equations were used to calculate glomerular filtration rate (GFR) and the associations between GFR and age were explored. RESULTS: The yearly change in cystatin C estimated GFR was 1.24 mL/min/1.73 m(2) while the corresponding decline for creatinine estimated GFR was 0.76 mL/min/1.73 m(2) for MDRD and 0.99 mL/min/1.73 m(2) for CKD-EPI. CONCLUSIONS: The age related association with GFR estimates is smaller for creatinine estimates than for cystatin C estimates. This leads to differences in the number of patients with reduced eGFR detected with the three estimates and the patient treatment will depend on the estimate used. This is not coherent with a good patient care and we thus need to develop new eGFR equations with better agreement between the estimates.

Particle enhanced turbidimetric immunoassay for the determination of urine cystatin C on Cobas c501.

OBJECTIVE: Urinary cystatin C has been reported to be a good marker for tubular damage and acute kidney injury. The aim of this study was to develop a high throughput assay for the quantification of urine cystatin C. METHODS: Antigen-excess, imprecision, interference, linearity, recovery, sample stability and reference values were evaluated on Cobas c501. RESULTS: The assay was linear over the dynamic range of the study (R²=0.9994). The total assay imprecision was below 5%. The assay recovery was estimated at 87-100%. No tendency to antigen-excess (up to 35 mg/L), nor interference with haemoglobin (1.25-10 g/L) was observed. Cystatin C was stable for 1 day at ambient temperature (19-23°C) but for 2 days at +4°C. The reference interval for cystatin C in urine was <0.414 mg/L. CONCLUSIONS: The urinary cystatin C assay verified to be a reliable assay with convenient performance characteristics, enabling routine testing on clinical chemistry platforms.

Determination of cerebrospinal fluid cystatin C on Architect ci8200.

BACKGROUND: Human cystatin C is a cysteine protease inhibitor produced by all nucleated cells in the body and the protein is present in all body fluids. The concentration in cerebrospinal fluid (CSF) is considerably higher than in plasma. Cystatin C levels seem to influence the development of Alzheimer disease (AD) and low levels in the brain are associated with an increased risk for AD. The aim of this study was to develop a high throughput assay for the quantification of cystatin C in CSF. METHODS: Antigen excess, imprecision, interference, linearity, recovery, sample stability and reference values were evaluated on Architect ci8200 (Abbott Laboratories, Abbott Park, IL, USA). RESULTS: The assay had an antigen-excess limit at 23 mg/L and was linear over the range of 0.84 to 8.33 mg/L. Results > 8.33 mg/L were automatically rerun in a higher dilution. Within-run coefficient of variation (CV) was 1.71, 1.10 and 0.79%, between day CV was 1.71, 0.39 and 1.45%, between-run CV was 0.58, 0.66 and 0.48%, and total CV was 2.49, 1.34 and 1.72% at cystatin C concentrations of 1.39, 3.17 and 6.28 mg/L, respectively. The recovery was 97-102%. No interference at a 7.5% deviation level was observed for 8.5 g/L of hemoglobin or 800 mg/L (1368 micromol/L) of bilirubin. Reference values for cystatin C in cerebrospinal fluid obtained with this method were 2.42-14.33 mg/L.

Performance evaluation of a particle-enhanced turbidimetric cystatin C assay on the Abbott ci8200 analyzer.

OBJECTIVES: Glomerular filtration rate (GFR) is widely accepted as the best overall measure of kidney function. Cystatin C is a novel endogenous GFR marker that has been shown to be superior to creatinine for estimation of GFR in several studies. There is a need for cystatin C assays adapted to routine chemistry instrument to minimize turnaround times and allowing 24 h/day availability. MATERIALS AND METHODS: We have evaluated a new cystatin C assay developed for Architect cSystem (Abbott Laboratories, Abbott Park, IL, USA). RESULTS: The cystatin C assay showed good agreement with the corresponding assay from Dade Behring (Deerfield, IL, USA). The assay has a very low total imprecision and a good linearity. CONCLUSIONS: The new cystatin C assay is an interesting alternative to current cystatin C assays. On an Architect cSystem the assay can be performed with the same turnaround times and availability as creatinine.

Patient selection has a strong impact on cystatin C and Modification of Diet in Renal Disease (MDRD) estimated glomerular filtration rate.

OBJECTIVE: Estimation of the glomerular filtration rate (GFR) is essential for the evaluation of patients with kidney disease, and for correct dosage of drugs that are eliminated from the circulation by the kidneys. In most cases GFR is estimated based on serum creatinine and the Modification of Diet in Renal Disease (MDRD) formula. As both cystatin C and creatinine are used for the determination of GFR it is important to investigate if estimated GFR by the two methods differ in various patient groups. DESIGN AND METHODS: We have compared cystatin C and MDRD estimated GFR calculated from the same request from primary care units (n=488), a cardiology ward (n=826), the cardiointensive care unit (n=1026), two oncology wards (n=919 and 1021), and the neurosurgical intensive care unit (n=1515) in an observational cross-sectional study. RESULTS: We found better agreement between the two GFR estimates in samples from primary care patients and patients in the cardiology wards, than in samples from oncology wards or the neurosurgical intensive care unit. In the latter settings there was a pronounced difference between the two GFR estimates. CONCLUSION: The comparisons show that differences in patient selections have a strong impact on the agreement between cystatin C and MDRD estimated glomerular filtration rate.

Comparison between chicken and rabbit antibody based particle enhanced cystatin C reagents for immunoturbidimetry.

We have compared three commercial particle enhanced cystatin C reagents. One of the reagents utilizes chicken antibodies and the other two reagents are rabbit antibody based. We show that the chicken antibody based reagent yields a higher delta absorbance when reacting with the antigen. IgY coupled to latex particles show a strong scatter response even at high antigen concentrations in contrast to the steep decline in scatter previously reported for IgY antibodies in solution. The reagent also showed a low CV for duplicate samples. Laying hens thus seems as an interesting source of antibodies for particle-enhanced immunoassays.

Performance characteristics of a cystatin C immunoassay with avian antibodies.

BACKGROUND: A new particle-enhanced turbidimetric immunoassay (PETIA) with avian antibodies for measuring serum/plasma cystatin C has been developed. The performance characteristics of the assay are described. METHODS: Measurements were performed on a Roche Modular P and on an Abbott Architect ci8200 using Gentian cystatin C immunoassay. RESULTS: Measuring range was 0.3-8.0 mg/L. Reference range was 0.57-1.09 mg/L. Total analysis time was 10 minutes. Linearity was absolute over the whole assay range. Recovery of samples and controls was within 98.6-109.4%. Total imprecision CV, measured over 20 days with two lots, was < or = 4.2%. Comparison with a particle enhanced nephelometric cystatin C immunoassay (PENIA) by linear regression resulted in a slope within 0.97-1.02 and intercept within +/-0.05 mg/L. Interference studies with drugs, anticoagulants, intralipid (< or = 11 g/L), triglycerides (< or = 14 g/L) and bilirubin (< or = 420 mg/L) showed no significant interference. Due to the use of avian antibodies, no interference with rheumatoid factor was observed. No carry-over was detected. Lower detection limit and lower quantification limit (CV < or = 6%) were both below 0.33 mg/L, which is less than the lowest standard. Sample stability was up to one month at 2-8 degrees C. Stability of the reagents at 2-8 degrees C was estimated to be 24 months. Stability of the reagents in use was minimum 9 weeks. CONCLUSIONS: Gentian cystatin C PETIA is shown to have excellent performance between methods . Interference results are improved due to avian antibodies and a broader span of the calibration curve. Avian antibodies are also known to have better immune response than mammalian antibodies towards mammalian antigens.

Variations in assay protocol for the Dako cystatin C method may change patient results by 50% without changing the results for controls.

BACKGROUND: Cystatin C is increasingly used as a glomerular filtration marker, but so far only a few companies produce most of the cystatin C reagents suited for turbidimetry or nephelometry use in clinical laboratories. METHODS: We studied different protocols for measuring cystatin C on an Architect ci8200 system using cystatin C reagents from Dako (Glostrup, Denmark). The results were compared with those obtained with Dade Behring reagents (Deerfield, IL, USA) on a BN ProSpec system. RESULTS: Differences in assay protocol on the same instrument with the Dako reagent yielded an up to 50% difference in glomerular filtration rate calculated from the cystatin C results when analyzing patient samples, but had no effect on the results for controls. There were also significant differences regarding linearity and kinetics between samples and controls/calibrators. CONCLUSIONS: The results indicate different reactivity of the Dako antibodies against calibrators and controls in comparison with patient samples, highlighting the importance of using controls and calibrators that do not differ from patient samples.