A review of Bland-Altman difference plot analysis in the veterinary clinical pathology laboratory

Current guidelines recommend using Bland-Altman plots (BA-plots), also called Difference plots, as part of method comparison evaluation in the veterinary clinical pathology laboratory. Analysis of differences can meaningfully augment linear regression techniques and allows fuller summarization of the performance of two methods relative to each other. This work summarizes the current literature on BA-plot composition and evaluation. Model data is used to demonstrate data evaluation approaches based on the observed differences, the combined inherent imprecision of the methods, and clinically relevant performance goals. Common limitations of the approaches, including points of frequent misinterpretation, are presented. BA-plot analysis can be part of an intentionally crafted method comparison study that provides analytically and clinically relevant data.

Mass Spectrometry-Based Evaluation of the Bland-Altman Approach: Review, Discussion, and Proposal

Reliable quantification in biological systems of endogenous low- and high-molecular substances, drugs and their metabolites, is of particular importance in diagnosis and therapy, and in basic and clinical research. The analytical characteristics of analytical approaches have many differences, including in core features such as accuracy, precision, specificity, and limits of detection (LOD) and quantitation (LOQ). Several different mathematic approaches were developed and used for the comparison of two analytical methods applied to the same chemical compound in the same biological sample. Generally, comparisons of results obtained by two analytical methods yields different quantitative results. Yet, which mathematical approach gives the most reliable results? Which mathematical approach is best suited to demonstrate agreement between the methods, or the superiority of an analytical method A over analytical method B? The simplest and most frequently used method of comparison is the linear regression analysis of data observed by method A (y) and the data observed by method B (x): y = α + βx. In 1986, Bland and Altman indicated that linear regression analysis, notably the use of the correlation coefficient, is inappropriate for method-comparison. Instead, Bland and Altman have suggested an alternative approach, which is generally known as the Bland-Altman approach. Originally, this method of comparison was applied in medicine, for instance, to measure blood pressure by two devices. The Bland-Altman approach was rapidly adapted in analytical chemistry and in clinical chemistry. To date, the approach suggested by Bland-Altman approach is one of the most widely used mathematical approaches for method-comparison. With about 37,000 citations, the original paper published in the journal The Lancet in 1986 is among the most frequently cited scientific papers in this area to date. Nevertheless, the Bland-Altman approach has not been really set on a quantitative basis. No criteria have been proposed thus far, in which the Bland-Altman approach can form the basis on which analytical agreement or the better analytical method can be demonstrated. In this article, the Bland-Altman approach is re-valuated from a quantitative bioanalytical perspective, and an attempt is made to propose acceptance criteria. For this purpose, different analytical methods were compared with Gold Standard analytical methods based on mass spectrometry (MS) and tandem mass spectrometry (MS/MS), i.e., GC-MS, GC-MS/MS, LC-MS and LC-MS/MS. Other chromatographic and non-chromatographic methods were also considered. The results for several different endogenous substances, including nitrate, anandamide, homoarginine, creatinine and malondialdehyde in human plasma, serum and urine are discussed. In addition to the Bland-Altman approach, linear regression analysis and the Oldham-Eksborg method-comparison approaches were used and compared. Special emphasis was given to the relation of difference and mean in the Bland-Altman approach. Currently available guidelines for method validation were also considered. Acceptance criteria for method agreement were proposed, including the slope and correlation coefficient in linear regression, and the coefficient of variation for the percentage difference in the Bland-Altman and Oldham-Eksborg approaches.

Evaluation of a point-of-care benchtop analyzer for quantitative measurement of C-reactive protein in canine serum and plasma

BACKGROUND

Canine C-reactive protein (cCRP) is an acute-phase protein that increases dramatically with inflammation and has potential utility in monitoring disease progression and response to treatment. Rapid, automated point-of-care test (POCT) formats could enhance the clinical utility of cCRP measurement.

OBJECTIVES

We aimed to evaluate the VetChroma canine-specific POCT assay for the quantitative measurement of cCRP in canine serum or plasma.

METHODS

Serum and plasma from discarded canine diagnostic samples were used. Evaluation included intra- and inter-assay coefficients of variation and observed total error (TE_obs ), linearity and spike recovery, the effect of interfering substances and sample matrices, and a method comparison study.

RESULTS

Intra-assay variation ranged from 2.5%-6.1%, and inter-assay variation ranged from 2.1%-5.4%. The TE_obs ranged from 15.1%-19.7%. The assay was linear over the manufacturer's analytical range with no evidence of constant or proportional bias. Recovery of purified cCRP from canine serum ranged from 116.2% to 138.4%. Hemolysis, icterus, and turbidity did not interfere with the assay. The comparison of paired plasma and serum samples revealed constant and proportional bias. Comparison of the VetChroma cCRP assay to a commercial cCRP ELISA revealed significantly different results.

CONCLUSIONS

The VetChroma cCRP assay has acceptable test performance to measure serum cCRP concentration. The POCT protocol and test kit are valid for clinical use, although results obtained using other cCRP assays or plasma may not be directly compared.

Evaluation of the Atellica TnIH cardiac troponin I assay and assessment of biological equivalence

OBJECTIVES

We evaluated the analytical performance characteristics and the biological equivalence of the Atellica TnIH assay.

METHODS

Precision, detection capability, linearity, and sex specific 99^th percentiles were determined de novo. Classification of patients relative to the 99^th percentiles was used to assess biological equivalence.

RESULTS

Analytical precision and detection capability of the Atellica TnIH assay is excellent with a limit of blank <1 ng/L and 62.5% of women and 93% of men had results above the limit of detection. The 99th percentiles (90% CI) in women were 49 ng/L (31-67) and 70 ng/L (48-121) in men. An asymmetrical distribution involving 5% of results was notable. Agreement was moderate (Kappa 0.58, 95% CI 0.53-0.63) with 20% of patients discordantly classified with Atellica TnIH below and Access hsTnI above the 99th percentiles. Serial results in 195 patients demonstrated good agreement (Kappa 0.84, 95% CI 0.77-0.90). Differences greater than the assay specific reference change values (z_≥±1.96) occurred in 65% (95% CI 53-76%) of 99th percentile discordant patients compared to 2.7% (p<0.001) and 76% (p=0.17) of the concordant low and high cTnI groups respectively.

CONCLUSIONS

The 99th percentile discordant and the concordantly elevated groups are more alike with respect to their z_≥±1.96 rates. This favours an overestimated Atellica TnIH 99th percentile as more likely, and we hypothesize that antibody interference resulting in asymmetric scatter of nearly 5% samples may be the underlying mechanism. Analytical accuracy and interferences in cardiac troponin assays should be investigated and resolved with high priority.

Method comparison of Particle Enhanced Immunoturbidimetry (PEIT) with High Performance Liquid Chromatography (HPLC) for glycated hemoglobin (HbA1c) analysis

BACKGROUND AND OBJECTIVE

High Performance Liquid Chromatography (HPLC) technique is considered as a gold standard for HbA1c analysis however all laboratories cannot adopt it due to certain limitations. Our aim was to compare Particle Enhanced Immunoturbidimetry (PEIT) method with High Performance Liquid Chromatography (HPLC) for HbA1c analysis.

METHOD

All blood samples were analyzed by HPLC assay on a Bio-Rad D-10 analyzer and PEIT on an Erba XL-200 analyzer. Precision studies were undertaken and Coefficient of Variation (%CV) calculated. Systemic Error (SE), Random Error (RE) and Total Error (TE_calc) were obtained. The Total Allowable Error (TEa) set by the National Glycohemoglobin Standardization Program (NGSP) for HbA1c is 6%.The acceptable evaluation method is where TE_calc is less than TE_a. RESULTS: The Precision studies were satisfactory with Coefficient of Variation (%CV) being less than 4% for both techniques. Mean HbA1c levels were slightly higher from HPLC than PEIT 9.07 ± 2.23% and 8.93 ± 2.10% respectively, although the difference was minimal. RE was 1.41%, TE_calc was 1.55%, which was less than TEa set by the NGSP. Both methods strongly correlated with the correlation coefficient (r) 0.9716, p < 0.0001.

CONCLUSION

Our study showed HbA1c analysis by PEIT technique is precise, accurate, rapid and convenient and can be employed as an alternative to HPLC technique in countries where cost is a major problem for diagnosis and treatment.

Comparison of Hematological and Biochemical Results Derived from Arterial and Venous Blood Samples in Post-Anesthetic Dogs

Simple Summary

In contrast to humans, general anesthesia is required for both surgical procedures and diagnostic imaging like magnetic resonance imaging (MRI) and computed tomography (CT) in small animals. Because the post-anesthetic period is a particularly high risk time for death, serial monitoring of biochemical and hematological parameters could be required. Blood samples could be collected from an indwelling arterial catheter to avoid stress caused by venipuncture, but studies using arterial blood for hematological and biochemical testing have been limited. The aim of this study is to compare hematological and biochemical results derived from venous and arterial blood samples, and to evaluate their clinical interchangeability in post-anesthetic dogs. We found statistically significant but clinically irrelevant differences in hemoglobin, glucose, creatinine, and calcium levels, and results from venous and arterial blood samples are not clinically interchangeable for gamma-glutamyl transpeptidase and potassium levels.

Abstract

Collecting blood from an indwelling arterial catheter may reduce stress from repeated venipuncture in patients requiring serial monitoring, but the use of arterial blood for hematological and biochemical testing remains understudied. Here, we compared hematological and biochemical results of arterial and venous blood and evaluated their clinical interchangeability. Blood samples from dogs who had recovered from anesthesia, collected by both arterial catheterization and venipuncture, were analyzed. To assess clinical acceptance between paired samples, the limit of agreement between the values derived from the arterial and venous blood samples was compared with the allowable total error (TEa) recommended for each parameter. We found no significant differences between the arterial and venous sample results for red/white blood cell and platelet counts and hematocrit, blood urea nitrogen, phosphate, total protein, albumin, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyl transpeptidase, total bilirubin, sodium, potassium, and chloride levels, whereas hemoglobin, glucose, creatinine, and calcium levels differed significantly (p < 0.05). Moreover, only gamma-glutamyl transpeptidase and potassium exceeded the recommended TEa. Hematological and biochemical results derived from venous and arterial blood samples are clinically interchangeable in post-anesthetic dogs, with the exception of gamma-glutamyl transpeptidase and potassium; thus, these values should be used with caution.

Blood Pressure, Congestion and Heart Failure with Preserved Ejection Fraction Among Patients with and Without Type 2 Diabetes Mellitus. A Cluster Analysis Approach from the Observational Registry DICUMAP

INTRODUCTION

The association of patients with heart failure (HF) and preserved ejection fraction (HFpEF) and with type 2 diabetes mellitus (T2DM) is strong and related additionally to blood pressure (BP).

AIMS

To analyze distinctive clinical profiles among patients with HFpEF both with and without T2DM.

METHODS

The study was based on a Spanish National Registry (multicenter and prospective) of patients with HF (DICUMAP), that enrolled outpatients with HF who underwent an ambulatory BP monitoring (ABPM) and then were followed-up for 1 year. We categorized patients according to the presence/absence of T2DM then building different clusters based on K-medoids algorithm.

RESULTS

103 patients were included. T2DM was present in 44.7%. The patients with T2DM were grouped into two clusters and those without T2DM into three. All patients with T2DM had kidney disease and anemia. Among them, cluster 2 had higher systolic blood pressure and pulse pressure (PP) with a bad outcome (p = 0.03) regarding HF mortality and readmissions, influenced by eGFR (HR 0.93, 95% CI 0.97-0.87, p = 0.04), and hemoglobin (HR 0.65, 95% CI 0.71-0.63, p = 0.03). Among those without T2DM, cluster 3 had a pathological ABPM pattern with the highest PP, cluster 4 was slightly similar to cluster 2, and cluster 5 expressed a more benign pattern without differences on both, HF mortality and readmissions.

CONCLUSIONS

Patients with HFpEF and T2DM expressed two different profiles depending on neurohormonal activation and arterial stiffness with prognostic implications. Patients without T2DM showed three profiles depending on ABPM pattern, kidney disease and PP without prognostic repercussion.

Potency evaluation of rabies vaccine for human use: The impact of reducing the number of animals per dilution - Part 2

The most critical parameter for the quality control of the rabies vaccine is potency, which is evaluated by challenge test in mice while using a large animal number. Because the 3Rs concept is applied worldwide, it becomes necessary to develop alternative methods to demonstrate the production consistency of these vaccines and reduce the number of animals used for performing assays. Hence, the present study evaluated the impacts of reducing the number of mice used in the NIH test for such vaccines. A retrospective data analysis compared vaccines tested in the standard test with the results of the reduced test using only the first cages of each dilution and considering the second cages as their replicates. The relevance of the reduced assay was evaluated using Bland- Altman plot and CCC. Reliability was assessed by CV% and confidence intervals, while the impact of the reduced mouse number was evaluated by the analysis of the confidence interval of potency results and regression, linearity and parallelism parameters. The results demonstrated the feasibility of reducing to eight mice per dilution in routine assays, with complete statistical validation of the resulting potency, allowing the number of animals used for the test vaccines to be reduced by 50%.

Comments on: "Comparison of Methods Study between a Photonic Crystal Biosensor and Certified ELISA to Measure Biomarkers of Iron Deficiency in Chronic Kidney Disease Patients"

We recently read, with great interest, the article entitled "Comparison of Methods Study between a Photonic Crystal Biosensor and Certified ELISA to Measure Biomarkers of Iron Deficiency in Chronic Kidney Disease Patients" [...].

Preanalytical stability of [-2]proPSA in whole blood stored at room temperature before separation of serum and plasma: implications to Phi determination

Background [-2]proPSA seems to outperform free/total prostate-specific antigen (PSA) ratio in prostate cancer diagnosis. However, [-2]proPSA stability remains an underestimated issue. We examined [-2]proPSA stability over time in whole blood before separation of serum and plasma and its implications for prostate health index (Phi) determination. Total PSA (tPSA) and free PSA (fPSA) stabilities were also assessed. Methods Blood was drawn from 26 patients and separated in two tubes for plasma (K2EDTA and K2EDTA plus protease inhibitors - P100) and one for serum (clot activator plus gel separator). Tubes were stored at room temperature before centrifugation 1, 3 and 5 h for serum and EDTA plasma or 1 and 5 h for P100 plasma. To investigate the influence of gel separator on markers' stability, blood was collected from 10 patients in three types of tubes to obtain serum: tubes with clot activator plus gel separator, with silica particles or glass tubes. Biomarkers were assayed with chemiluminescent immunoassays. Results [-2]proPSA and Phi levels significantly and progressively increased over time in serum (+4.81% and +8.2% at 3 h; +12.03% and +14.91% at 5 h, respectively, vs. 1 h; p<0.001). Conversely, [-2]proPSA levels did not change in plasma (EDTA or P100). tPSA levels did not change over time in serum or plasma, whereas fPSA decreased in serum. All markers were higher in plasma than in serum at any time point. This difference did not seem to be attributable to the use of gel for serum preparation. Conclusions EDTA prevented spurious in vitro modifications in PSA-related isoforms, confirming that a stabilized blood sample is a prerequisite for [-2]proPSA measurement and Phi determination.

The use of error and uncertainty methods in the medical laboratory

Error methods - compared with uncertainty methods - offer simpler, more intuitive and practical procedures for calculating measurement uncertainty and conducting quality assurance in laboratory medicine. However, uncertainty methods are preferred in other fields of science as reflected by the guide to the expression of uncertainty in measurement. When laboratory results are used for supporting medical diagnoses, the total uncertainty consists only partially of analytical variation. Biological variation, pre- and postanalytical variation all need to be included. Furthermore, all components of the measuring procedure need to be taken into account. Performance specifications for diagnostic tests should include the diagnostic uncertainty of the entire testing process. Uncertainty methods may be particularly useful for this purpose but have yet to show their strength in laboratory medicine. The purpose of this paper is to elucidate the pros and cons of error and uncertainty methods as groundwork for future consensus on their use in practical performance specifications. Error and uncertainty methods are complementary when evaluating measurement data.

Comparison of Methods Study between a Photonic Crystal Biosensor and Certified ELISA to Measure Biomarkers of Iron Deficiency in Chronic Kidney Disease Patients

The total analytical error of a photonic crystal (PC) biosensor in the determination of ferritin and soluble transferrin receptor (sTfR) as biomarkers of iron deficiency anemia in chronic kidney disease (CKD) patients was evaluated against certified ELISAs. Antigens were extracted from sera of CKD patients using functionalized iron-oxide nanoparticles (fAb-IONs) followed by magnetic separation. Immuno-complexes were recognized by complementary detection Ab affixed to the PC biosensor surface, and their signals were followed using the BIND instrument. Quantification was conducted against actual protein standards. Total calculated error (TEcalc) was estimated based on systematic (SE) and random error (RE) and compared against total allowed error (TEa) based on established quality specifications. Both detection platforms showed adequate linearity, specificity, and sensitivity for biomarkers. Means, SD, and CV were similar between biomarkers for both detection platforms. Compared to ELISA, inherent imprecision was higher on the PC biosensor for ferritin, but not for sTfR. High SE or RE in the PC biosensor when measuring either biomarker resulted in TEcalc higher than the TEa. This did not influence the diagnostic ability of the PC biosensor to discriminate CKD patients with low iron stores. The performance of the PC biosensor is similar to certified ELISAs; however, optimization is required to reduce TEcalc.

Choosing a new CD4 technology: Can statistical method comparison tools influence the decision?

BACKGROUND

Method comparison tools are used to determine the accuracy, precision, agreement, and clinical relevance of a new or improved technology versus a reference technology. Guidelines for the most appropriate method comparison tools as well as their acceptable limits are lacking and not standardized for CD4 counting technologies.

METHODS

Different method comparison tools were applied to a previously published CD4 dataset (n = 150 data pairs) evaluating five different CD4 counting technologies (TruCOUNT, Dual Platform, FACSCount, Easy CD4, CyFlow) on a single specimen. Bland-Altman, percentage similarity, percent difference, concordance correlation, sensitivity, specificity and misclassification method comparison tools were applied as well as visualization of agreement with Passing Bablock and Bland-Altman scatter plots.

RESULTS

The FACSCount (median CD4 = 245 cells/µl) was considered the reference for method comparison. An algorithm was developed using best practices of the most applicable method comparison tools, and together with a modified heat map was found useful for method comparison of CD4 qualitative and quantitative results. The algorithm applied the concordance correlation for overall accuracy and precision, then standard deviation of the absolute bias and percentage similarity coefficient of variation to identify agreement, and lastly sensitivity and misclassification rates for clinical relevance.

CONCLUSION

Combining method comparison tools is more useful in evaluating CD4 technologies compared to a reference CD4. This algorithm should be further validated using CD4 external quality assessment data and studies with larger sample sizes. © 2017 International Clinical Cytometry Society.

Discordance with 3 Cardiac Troponin I and T Assays: Implications for the 99th Percentile Cutoff

BACKGROUND

We compared the 99th percentile reference intervals with 3 modern cardiac troponin assays in a single cohort and tested the hypothesis that the same individuals will be identified as above the cutoff and that differences will be explained by analytical imprecision.

METHODS

Blood was collected from 2005 apparently healthy blood donors. Cardiac troponin was measured with Abbott Architect STAT high sensitive troponin I, Beckman Coulter Access AccuTnI+3, and Roche Elecsys troponin T highly sensitive assays.

RESULTS

The 99th percentile cutoff limits were as follows: Abbott cardiac troponin I (cTnI) 28.9 ng/L; Beckman Coulter cTnI 31.3 ng/L; and Roche cardiac troponin T (cTnT) 15.9 ng/L. Correlation among the assays was poor: Abbott cTnI vs Beckman Coulter cTnI, R2 = 0.18; Abbott cTnI vs Roche cTnT, R2 = 0.04; and Beckman Coulter cTnI vs Roche cTnT R2 = 0.01. Of the results above the cutoff 50% to 70% were unique to individual assays, with only 4 out of 20 individuals above the cutoff for all 3 assays. The observed differences among assays were larger than predicted from analytical imprecision.

CONCLUSIONS

The 99th percentile cutoff values were in agreement with those reported elsewhere. The poor correlation and concordance amongst the assays were notable. The differences found could not be explained by analytical imprecision and indicate the presence of inaccuracy (bias) that is unique to sample and assay combinations. Based on these findings we recommend less emphasis on the cutoff value and greater emphasis on δ values in the diagnosis of myocardial infarction.

Dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and micro-computed tomography techniques are discordant for bone density and geometry measurements in the guinea pig

This study aims to examine agreement among bone mineral content (BMC) and density (BMD) estimates obtained using dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and micro-computed tomography (μCT) against high-resolution μCT and bone ash of the guinea pig femur. Middle-aged (n = 40, 86 weeks) male guinea pigs underwent in vivo followed by ex vivo DXA (Hologic QDR 4500A) scanning for intact and excised femur BMC and areal density. To assess bone architecture and strength, excised femurs were scanned on pQCT (Stratec XCT 2000L) as well as on two μCT scanners (LaTheta LCT-200; Skyscan 1174), followed by three-point bending test. Reproducibility was determined using triplicate scans; and agreement assessed using Bland-Altman plots with reference methods being high-resolution μCT (Skyscan) for BMD and bone ashing for BMC. All techniques showed satisfactory ex vivo precision (CV 0.05-4.3 %). However, bias compared to the reference method was highest (207.5 %) in trabecular bone volume fraction (BV/TV) measured by LaTheta, and unacceptable in most total femur and cortical bone measurements. Volumetric BMD (vBMD) and BV/TV derived by LaTheta and pQCT at the distal metaphysis were biased from the Skyscan by an average of 49.3 and 207.5 %, respectively. Variability of vBMD, BV/TV and cross-sectional area at the diaphysis ranged from -5.5 to 30.8 %. LaTheta best quantified total femur BMC with an upper bias of 3.3 %. The observed differences among imaging techniques can be attributable to inherent dissimilarity in construction design, calibration, segmentation and scanning resolution used. These bone imaging tools are precise but are not comparable, at least when assessing guinea pig bones.

[Measurement of canine and feline pancreatic lipase immunoreactivity - analytical comparison of new commercial assays with established assays]

OBJECTIVE

Commercial assays for the measurement of canine and feline pancreatic lipase immunoreactivity (Spec cPL® and Spec fPL®) have been available for a few years. The aim of this study was to compare new commercial assays that have not previously been validated in the literature to the established assays.

MATERIAL AND METHODS

Leftover serum samples from diagnostic submissions to the GI-lab of the Texas A&M University were collected based on certain parameters (e.g., good quality sample, hemolytic, lipemic, or icteric sample) and were assigned random sample ID numbers. The samples were evaluated by Spec cPL® or Spec fPL® and sent on dry ice to the Kleintierklinik am Hochberg (Germany). From here one aliquot of each sample was blindly submitted to the diagnostic laboratory Laboklin (Germany) for measurement of cPL and fPL by their newly released assay and also to the GI-Lab (Texas) for repeated analysis to exclude any effect of shipping.

RESULTS

There was no significant difference between serum cPL or fPL concentrations before or after shipping at the GI-Lab (Texas) (Wilcoxon paired sample signed rank tests p = 0.581 and 0.712, respectively). Significant differences were found between serum cPL or fPL concentrations of the newly released assays and the established assays (p < 0.0004 and p = 0.025, respectively). The newly released and the established assays showed some association (Spearman r: 0.775 and 0.739, respectively), however, there was a strong bias between the new assays and the established assays. The strength of agreement between the new and established canine and feline assays was poor (concordance coefficient 0.539 and 0.465, respectively). Also, the clinical interpretation for serum cPL and fPL results did not agree for many of the samples.

CONCLUSION AND CLINICAL RELEVANCE

In conclusion, the newly released assays for the measurement of cPL and fPL show significant bias and poor concordance and provide different clinical interpretations when compared with validated assays. Thus, further research is needed before these newly released assays can be recommended for clinical use.

Validation of equations used to predict plasma osmolality in a healthy adult cohort

BACKGROUND

Plasma osmometry and the osmol gap have long been used to provide clinicians with important diagnostic and prognostic patient information.

OBJECTIVE

We compared different equations used for predicting plasma osmolality when its direct measurement was not practical or an osmol gap was of interest and identified the best performers.

DESIGN

The osmolality of plasma was measured by using freezing point depression by microosmometer and osmolarity calculated from biosensor measures of select analytes according to the dictates of each formula tested. After a rigid analytic prescreen of 36 originally published equations, a bootstrap regression analysis was used to compare shrinkage and model agreement.

RESULTS

Sixty healthy volunteers provided 163 plasma samples for analysis. Of 36 equations considered, 11 equations met the prescreen variables for the bootstrap regression analysis. Of the 11 equations, 8 equations met shrinkage and apparent model error thresholds, and 5 equations were deemed optimal with an original model osmol gap <5 mmol.

CONCLUSIONS

The use of bootstrap regression provides a unique insight for osmolality prediction equation performance from a very large theoretical population of healthy people. Of the original 36 equations evaluated, 5 equations appeared optimal for the prediction of osmolality when its direct measurement was not practical or an osmol gap was of interest. Note that 4 of 5 optimal equations were derived from a nonhealthy population.

Severe experimental folate deficiency in a human subject - a longitudinal investigation of red-cell folate immunoassay errors as megaloblastic anaemia develops

Background

The few published studies comparing results between commercial red-cell folate immunoassays have found significant differences. None have provided longitudinal data during the development of megaloblastic anaemia from severe folate deficiency. The objective was to produce longitudinal data, comparing results between three commercial immunoassays for red-cell folate, generated by means of severe experimental folate deficiency.

Methods

This 58 year old male, initially replete in folate, used a folate-deficient diet to severely deplete himself of folate until overt megaloblastic anaemia developed. The Siemens Advia Centaur, Roche Elecsys 2010 and Beckman UniCel DxI 800 Access immunoassay systems were used, by different clinical pathology laboratories, to perform weekly assays for red-cell folate throughout the depletion stage. The results were analysed graphically four ways: comparison with lines of equality; number of standard deviations difference against the means; number of standard deviations difference over time; variation over time.

Results

There were very significant differences, varying with time and folate concentration, between the results reported by the three laboratories. The differences were greatest, up to 17 standard deviations, between the Siemens Advia Centaur and each of the other two systems. Of the 85 results comparing the Siemens Advia Centaur and the Roche Elecsys 2010, two were within the 99.9% confidence interval. Of the 91 results comparing the Siemens Advia Centaur and the Beckman UniCel DxI 800 Access, 22 were within the 99.9% confidence interval. Of the 83 results comparing the Beckman UniCel DxI 800 Access and the Roche Elecsys 2010, 37 were within the 99.9% confidence interval.

Conclusions

Comparative longitudinal data from clinical pathology laboratories, produced during experimental folate deficiency, have exposed very significant differences in results between commercial red-cell folate immunoassays. One immunoassay, the Roche Elecsys 2010, failed to detect overt megaloblastic anaemia of severe folate deficiency.

Electronic supplementary material

The online version of this article (doi:10.1186/2193-1801-3-441) contains supplementary material, which is available to authorized users.

[Postoperative assessment of daily energy expenditure. Comparison of two methods]

BACKGROUND

The reference method for determining resting energy expenditure (REE) in clinical nutrition practice is measurement by indirect calorimetry; however, indirect calorimetry has some limitations, is expensive and not widely available. Therefore, the most used methods to estimate the caloric requirements in intensive care patients are predictive equations. The Harris-Benedict equations (HBE) are the most common formulae in the clinical setting. The SenseWear(®) armlet (SWA) is a noninvasive device that monitors skin temperature, heat flux, galvanic skin response and movement. These data as well as anthropometric characteristics are used to calculate REE. The aim of this study was to evaluate the levels of agreement and interchangeability of REE estimated by HBE (EEHBE) and measured by SWA (EESWA) in normometabolic patients after elective bowel resection with laparotomy. Furthermore, postsurgical pain therapy by continuous thoracic epidural anaesthesia (t-PDA) was compared with continuous intravenous pain therapy regarding EESWA in these patients.

METHODS

After obtaining approval by the ethics committee and written informed consent 57 patients participated in the study procedures. A total of 50 patients (23 male, 27 female) were finally included in the data analysis because 7 patients did not meet the criterion of > 80% on-body time of the SWA. Additional (a priori) exclusion criteria were metabolic or cardiopulmonary decompensation or postoperative mechanical ventilation. Before induction of general anesthesia 26 patients received a thoracic epidural catheter. Immediately after surgery the SWA was placed on the right upper arm of each patient for 24 h. A continuous pain therapy was started either an epidural application of ropivacain 0.2% and sufentanil or in the other 24 patients an intravenous infusion of metamizol and tramadol.

RESULTS AND DISCUSSION

The data showed good agreement between EESWA and EEHBE. The mean on-body time was found to be 22.94±4.77 h. There were no significant differences between EESWA and EEHBE (p>0.05) corresponding to a high Pearson's coefficient of correlation of 0.985. The mean bias (EESWA-EEHBE) was -0.569±0.378 kcal/kgBW/24 h reflecting a minimal systematic underestimation of REE by SWA of -2.9% compared to EEHBE. The Bland-Altman plot shows interchangeability of EESWA and EEHBE. It was noted that 94% of the data points (47 out of 50 patients) were within ±2 SD and the remaining 3 data points were lying close to the 95% interval. The same results (no significant differences between EESWA and EEHBE) were obtained after differentiation of EEHBE into low (<18 kcal/kgBW/24 h, n=9), medium (18-21 kcal/kgBW/24 h, n=30) and high (>21 kcal/kgBW/24 h, n=11) energy ranges. There were no significant differences in EESWA regarding postsurgical pain therapy regimens.

CONCLUSIONS

The SWA showed reliable concordance with daily REE estimated by HBE in normometabolic postsurgery patients. This noninvasive, convenient and easy to handle device may be helpful in determining energy requirements as part of metabolic monitoring. Further research is needed to validate the method in patients with severe metabolic disturbances. The energetic requirements of patients with postoperative t-PDA were not different from those with intravenous pain therapy.

Evaluation of a microsphere-based immunofluorescence assay for the determination of Immunoglobulin A concentrations in cerebrospinal fluid of dogs

The simultaneous increase of immunoglobulin A (IgA) in serum and cerebrospinal fluid (CSF) is a characteristic finding in dogs suffering from canine steroid-responsive meningitis-arteritis (SRMA). The study aimed at developing and evaluating a microsphere-based immunofluorescence assay (MIA) for the measurement of IgA, trying to fulfill the need of a quicker method using only small volumes of CSF. Microsphere beads were coated with goat-anti-dog IgA antibodies and bound IgA was detected by a mouse-anti-dog IgA antibody in combination with a PE-labeled goat-anti-mouse IgG. CSF from 44 dogs were tested for IgA and compared with an in-house utilized ELISA. Using clinical relevant reference ranges, the new method showed a good agreement (84.17%) with the ELISA. A method comparison revealed a moderate agreement only. These findings indicate that the MIA will not replace the ELISA, but it opens the possibility for further research with microsphere-based assays.

Incurred sample reanalysis: different evaluation approaches on data obtained for spironolactone and its active metabolite canrenone

Background: The inherent reproducibility of a bioanalytical approach is usually sustained through incurred sample reanalysis (ISR). Questions relating to the number of ISRs, the right moment for performing reanalysis, the way of performing an appropriate statistical refinement of experimental data and actions to be taken in the case of failure are frequently raised. Results: Data resulting from ISR following a bioequivalence study for spironolactone formulations are discussed. Reanalysis of samples was carried out twice: immediately after the end of the study and after a period that overcame the long-term stability study achieved during method validation. The Bland–Altman approach was used to assess experimental results. ISR was successful over the short reanalysis period for both compounds. Data produced through reanalysis after the long-term period indicated a systematic positive bias for the metabolite canrenone (although results supported reproducibility). The results obtained for spironolactone were affected by a strong negative systematic bias and failed to support reproducibility. The explanation deals with the continuous conversion of spironolactone to canrenone in plasma samples. However, reproducibility of the method may be sustained by comparing original and repeated differences between concentration values in samples by means of a paired t-test, Wilcoxon sign rank-sum test and linear regression. Conclusions: Different statistical approaches for making data comparisons are discussed and may be successfully applied during reanalysis of samples from a bioequivalence study. Results of the evaluations may differ in accordance with the statistical procedure being applied, thus a definitive conclusion requires consideration of all specific experimental circumstances arising during production of the processed data.

Development and analytical validation of a radioimmunoassay for the measurement of alpha1-proteinase inhibitor concentrations in feces from healthy puppies and adult dogs

Canine α1-proteinase inhibitor (cα1-PI), a proteolysis-resistant protein with a molecular weight similar to albumin, has been shown to be clinically useful as a marker for gastrointestinal protein loss in dogs. A competitive, liquid-phase radioimmunoassay was developed and analytically validated. Fecal samples were collected from 101 healthy pet dogs of various breeds and ages, and fecal cα1-PI (Fcα1-PI) concentrations were compared between dogs of different age groups. A reference interval for Fcα1-PI concentration was calculated using the central 95th percentile. Analytical sensitivity of the assay was 2.2 µg Fcα1-PI/g feces. Observed-to-expected ratios for the serial dilution and spiking recovery of 9 and 6 fecal extracts ranged from 90.4 to 152.0% and from 71.3 to 112.3%, respectively. Coefficients of variation for intra- and interassay variability for 6 fecal extracts were ≤10.8% and ≤12.5%, respectively. The reference intervals for the mean and maximum Fcα1-PI from fecal samples collected on 3 consecutive days were 2.2–13.9 µg/g and 2.2–21.0 µg/g, respectively. Fcα1-PI was significantly higher in dogs <1 year of age ( P < 0.0001 for both mean and maximum Fcα1-PI for the 3 samples). The radioimmunoassay described is sensitive, linear, precise, reproducible, and accurate for clinical use, thus allowing reliable quantification of Fcα1-PI in clinical patients. Using this assay, a mean or a maximum Fcα1-PI for 3 sampling days of >13.9 µg/g or >21.0 µg/g, respectively, should be considered abnormal in dogs >1 year of age. Fecal cα1-PI concentrations in dogs <1 year of age were significantly higher and should be carefully interpreted in this age group.

Incurred sample reanalysis (ISR): a decisive tool in bioanalytical research

The AAPS Workshop 2008 on Current Topics in GLP Bioanalysis: Assay Reproducibility for Incurred Samples was the defining moment in establishing incurred sample reanalysis (ISR) as a mandatory exercise in demonstrating assay reproducibility using incurred (study) samples. The importance of ISR can be envisaged from its role in clinical as well as non-clinical studies. Incurred samples can differ significantly in their composition when compared with the calibration standards and quality control samples that are used to validate the developed method. The present article attempts to summarize five troubleshooting cases encountered in the analyses of incurred samples for bioanalytical methods developed in our laboratory for mesalamine, hydrochlorothiazide, clopidogrel, sildenafil and rabeprazole. The issues identified were related to: sample inhomogeneity, sample processing error, impact of buffer pH during sample preparation, instability of metabolite and change in laboratory environment. The steps taken to trace and correct these incidents are discussed with adequate data. These examples will further broaden the scope and emphasize the significance of ISR. We believe this investigation will help to develop more reliable and efficient bioanalytical methods.

Agreement between the Heidelberg Retina Tomograph (HRT) stereometric parameters estimated using HRT-I and HRT-II

PURPOSE

To assess agreement between Heidelberg Retina Tomograph (HRT)-I and HRT-II stereometric parameters and to determine whether parabolic error correction (PEC) to the topographies improves agreement.

METHODS

University of California San Diego Diagnostic Innovations in Glaucoma Study participants with two HRT-II examinations (n = 380) or one HRT-I and one HRT-II examinations (n = 344) acquired on the same day were included. From the group of 380 eyes, 200 eyes were randomly selected to estimate the repeatability coefficients of HRT-II rim area and volume, cup area and volume, and mean retinal nerve fiber layer (RNFL) thickness parameters (HRT-II control group), and the remaining 180 eyes were used to assess agreement between two HRT-II examinations (HRT-II study group). Agreement between stereometric parameters of HRT-I and HRT-II examinations (HRT-I vs. HRT-II study group) were assessed with (1) no PEC, (2) HRT PEC, and (3) a modified PEC. Bland-Altman plots were used to assess agreement using estimates of bias and clinical limits of agreement (CLA) based on repeatability coefficients.

RESULTS

In the HRT-II study group, agreement between stereometric parameters was good, with no statistically significant biases. For all parameters, differences were within the CLA in 94% of participants. In the HRT-I vs. HRT-II study group, there was a small statistically significant bias between the stereometric parameters, but all differences were within CLA for ≥95% of participants. In both study groups, PEC did not improve agreement.

CONCLUSIONS

Agreement between HRT-I and HRT-II stereometric parameters was good, and PEC did not improve agreement. These results suggest that HRT-I and HRT-II examinations can be used interchangeably to detect changes in stereometric parameters over time.

Comparing body composition assessment tests in long-term hemodialysis patients

BACKGROUND

Protein-energy wasting is common in chronic kidney disease and is associated with decreases in body muscle and fat stores and poor outcomes. The accuracy and reliability of field methods to measure body composition is unknown in this population.

STUDY DESIGN

Cross-sectional observational study.

SETTING & PARTICIPANTS

118 maintenance hemodialysis patients were seen at the General Clinical Research Center at Harbor-UCLA Medical Center, Torrance, CA.

INDEX TESTS

Triceps skinfold, near-infrared interactance, and bioelectrical impedance analysis using the Segal, Kushner, and Lukaski equations.

REFERENCE TEST

Dual-energy x-ray absorptiometry (DEXA).

RESULTS

Participants (42% women, 52% with diabetes, 40% African Americans, and 38% Hispanics) were aged 49.4 +/- 11.5 (mean +/- SD) years, and had undergone dialysis therapy for 41.1 +/- 32.9 months. Body mass index was 27.0 +/- 6.0 kg/m(2). Using DEXA as the reference test, the bioelectrical impedance analysis-Kushner equation, triceps skinfold, and near-infrared interactance were most accurate of the index tests in estimating total-body fat percentage, whereas bioelectrical impedance analysis-Segal equation and bioelectrical impedance analysis-Lukaski equation overestimated total body fat percentage. Bland-Altman analyses and difference plots showed that bioelectrical impedance analysis-Kushner and near-infrared interactance were most similar to the reference test. Bioelectrical impedance analysis-Kushner, triceps skinfold, and near-infrared interactance had the smallest mean differences from DEXA, especially in women (1.6%, 0.7%, and 1.2%, respectively). Similar results were observed in African American participants (n = 47).

LIMITATIONS

Measurements were performed 1 day after a hemodialysis treatment, leading to more fluid retention, which may have affected the reference and index tests differently.

CONCLUSIONS

Using DEXA as the reference test, both near-infrared interactance and bioelectrical impedance analysis-Kushner method yield more consistent estimates of total body fat percentage in maintenance hemodialysis patients compared with the other index tests. Near-infrared interactance is not affected by skin color. Field methods with portable devices may provide adequate precision.

Assessment of salivary urea as a less invasive alternative to serum determinations

OBJECTIVE

Experimental studies describe how urea is excreted through salivary glands and correlates with serum levels independently of salivary flow rate. This study confirms that salivary urea (SaU) is a reliable biomarker of uraemic state. In order to validate the SaU methodology, the following factors were taken into account: the independence of urea levels from saliva flow rate in healthy subjects and patients with chronic renal failure and the agreement between SaU and serum urea (U) levels in the entire population. In addition, reference intervals and cut-off values for SaU and U were established.

MATERIAL AND METHODS

Urea levels were determined in 268 matched whole saliva (SaU) and serum (U) samples obtained simultaneously from 78 healthy individuals and 154 patients with chronic renal failure. A serum enzymic colorimetric assay was adapted to SaU determinations.

RESULTS

SaU was independent of salivary flow rate. The agreement between SaU and U was confirmed by Bland-Altman analysis with a significant correlation between them (r = 0.91, p = 0.0001). The reference interval of SaU ranged from 1.66 to 7.5 mM. The cut-off values for SaU and U were 7.5 mM and 8.2 mM, respectively (sensitivity and specificity 100% for both).

CONCLUSIONS

SaU testing is harmless and useful for ruling out azotemic states in outpatients. Our results support the inclusion of SaU as a diagnostic test in the clinical laboratory.

Incurred sample reanalysis: enhancing the Bland–Altman approach with tolerance intervals

This article describes the need for incurred sample reanalysis and suggests that the combination of a Bland–Altman plot and tolerance intervals can provide a visual evaluation of method performance. It also shows how the proposed combination is a tool that may be of value in determining minimum sample size. An example dataset is worked through in its entirety so that a reader unfamiliar with the topic can gain sufficient information to analyze their own data. Related topics include the generation of 66.7% tolerance factors, comparison of mean-normalized and log differences and the use of probability plots to evaluate error distributions. The suggestions presented in this article are meant to be a continuation of the ongoing incurred sample reanalysis discussion and, as such, further comment is invited.

Portable biomedical devices: a critical issue during telecare services design

OBJECTIVES

The selection of a portable biomedical device (PBD) is a key issue regarding telecare service design. The objective of this study is to investigate the accuracy parameters of a PBD under different settings and levels.

METHODS AND MATERIALS

By using a commercial PBD, trials were performed in a referral cardiology center and on the Olympia Explorer of the Royal Olympia Cruises, and the Superfast XII of Superfast Ferries. Data were collected (February 2004 - June 2006) by performing: (1) 'in hospital' standalone trials; (2) 'in hospital' comparative trials; and (3) 'on board' trials. Semistructured interviews were also conducted with several subjects, their cardiologists and crewmembers.

RESULTS

We investigated the accuracy parameters, namely the data precision (DP), the peripheral modules reliability (PMR) and the data transmission quality (DTQ). Although the outcomes of the comparative trials, via a statistical method verifying the DP (more than 95%), the trials 'on board' and 'in hospital' revealed a number of critical variables for the PMR and DTQ parameters.

CONCLUSION

Telecare services design has accuracy parameter investigation needs. These parameters should be investigated simultaneously, while a compromise between them can act as a driving force to the telecare services success. The compromise is achieved by a smooth fit between DP and PMR with this fit varying within settings and levels.

Preservation of RNA for functional analysis of separated alleles in yeast: comparison of snap-frozen and RNALater solid tissue storage methods

BACKGROUND

The aim of the present study was to compare RNALater with the usual method of liquid nitrogen snap freezing as a surrogate mRNA preservation method for functional analysis of separated alleles in yeast (FASAY).

METHODS

A total of 81 patients with transitional cell carcinoma of the bladder underwent fresh tissue biopsies directly transferred into RNALater and stored at room temperature or at 4 degrees C for increasing time intervals until RNA processing. From this cohort of patients, 53 paired snap-frozen and RNALater preservative-suspended tissues were obtained. Samples immediately frozen in liquid nitrogen were further stored at -80 degrees C.

RESULTS

Of the 81 RNALater samples, 14 were not processed for FASAY because of RNA degradation. Of the remaining 67 samples, 15 (22%) were FASAY-positive. Identical FASAY results were found for 50 of 53 (94.4%) paired samples and the percentage of red yeast colonies was highly correlated (Cohen's kappa<0.82; p<0.00001). A single p53 missense mutation was found in each of the three discordant positive FASAY and was identical in each concordant positive sample (10/53). Storing samples in RNALater at room temperature for 3 days and at 4 degrees C for less than 1 month provided high-quality mRNA suitable for FASAY.

CONCLUSIONS

Our results demonstrate that RNALater is a suitable and flexible alternative to snap freezing for FASAY analysis.

Salivary testosterone: a reliable approach to the diagnosis of male hypogonadism

OBJECTIVE

This study was to demonstrate that Sal-T is a reliable biomarker of androgen status in the diagnosis of male hypogonadism.

DESIGN

In order to validate the salivary testosterone assay (Sal-T), its reproducibility, the agreement with serum free testosterone levels (Free-T), the correlation with other circulating androgen markers (bioavailable testosterone, total testosterone) and cut-off values were defined.

PATIENTS AND METHODS

We studied 52 eugonadic (E) and 20 hypogonadic (Hy) men. Sal-T was assayed using an adapted radioimmunoassay for serum testosterone. Sal-T concentrations were compared in nine cases before and after citric acid stimulation of salivary flow rate. Free-T and bioavailable testosterone (Bio-T) were calculated by Vermeulen equation and SHBG were determined by binding assay.

RESULTS

Sal-T did not depend on salivary flow rate and morning samples from 07.00 h to 09.00 h were stable. Agreement between Sal-T and Free-T measurements was confirmed in all subjects. Sal-T levels correlated positively with all circulating androgens, showing the best correlation with Free-T in E (r = 0.92) as well as in Hy (r = 0.97). A cut-off value of Sal-T < or = 0.195 nm showed 100% sensibility and specificity to rule out hypogonadism.

CONCLUSIONS

Our data showed that Sal-T is a reliable marker of testosterone bioavailability. The results support the inclusion of this biomarker as a noninvasive approach in the diagnosis of male androgen deficiency.

Bias Estimation in Method Comparison Studies

A test and a reference analytical method are usually compared for agreement based on paired data obtained from several independent subjects. Bias between two methods can be classified as constant and proportional. In this article, we provide an approach for maximum likelihood estimation of total bias between two methods and partitioning it into constant and proportional bias for each subject. Normal, binomial, or Poisson distribution are the conditional distributions of the response variable that we have considered here, whereas subjects are considered to be random sample from a normally distributed population. Real data on blood cell counts and hemoglobin are used for demonstration. The estimate of biases can be used to test different statistical hypotheses and/or for graphical interpretation of the agreement. The partitioning of total biases in terms of constant and proportional gives an insight on the sources of disagreement between two methods and helps designers and manufacturer's define a remedial strategy.

Multiplexed quantification of dementia biomarkers in the CSF of patients with early dementias and MCI: a multicenter study

In this report we evaluated the clinical performance of APOE genotyping and three protein biomarkers (total tau, beta-amyloid(1-42), and tau phosphorylated at threonine 181) in a prospective multicenter study using the INNO-BIA AlzBio3 assay applied on Luminex platform. Concentration of biomarkers of Alzheimer's disease in cerebrospinal fluid (CSF) was measured with multiplexing technology (n=223), and compared to the results of ELISA assays in patients with early dementias or mild cognitive impairment (MCI) collected at 12 gerontopsychiatric university departments, and APOE genotyping was performed. Concentrations of Abeta(1-42) were statistically significantly lower in MCI-AD subjects compared to MCI-O, and significantly lower in D-AD patients compared to MCI-O. P-tau(181P) concentrations were significantly higher in MCI-AD patients compared to MCI-O, and significantly higher in D-AD patients compared to MCI-O. The total tau concentrations in MCI-AD patients were significantly higher compared to MCI-O, and higher in D-AD compared to MCI-O, moreover, the concentration of total tau was significantly higher in D-AD compared to MCI-AD patients. For the differential diagnosis between D-AD and D-O, the optimal cutoff concentration of Abeta(1-42) was 197.7 pg/mL, and that for P-tau(181P) was 47.9 pg/mL. These cutoff values were also applied to discriminate between MCI-AD and MCI-O subjects. Simultaneous measurement of the biomarkers significantly improves management of the samples and quality control of the assays' performance.

Nonaqueous capillary electrophoresis method for the enantiomeric purity determination of S-timolol using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin: validation using the accuracy profile strategy and estimation of uncertainty

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of S-timolol maleate using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) as chiral selector. With a background electrolyte made up of a methanolic solution of 0.75 M formic acid, 30 mM potassium camphorsulfonate and containing 30 mM HDMS-beta-CD, the determination of 0.1% of R-timolol in S-timolol could be performed with an enantiomeric resolution of 8.5. Pyridoxine was selected as internal standard. The NACE method was then fully validated by applying a novel strategy using accuracy profiles. It is based on beta-expectation tolerance intervals for the total measurement error which includes trueness and intermediate precision. The uncertainty of measurements derived from beta-expectation tolerance intervals was estimated at each concentration level of the validation standards. To confirm the suitability of the developed and validated method, several real samples of S-timolol maleate containing R-timolol maleate at different concentrations were analysed and the results were compared to those obtained by liquid chromatography.

Performance validation of a third-generation allergen-specific IgE assay in the clinical laboratory: Interlaboratory and intermethod comparison

BACKGROUND

Allergen-specific IgE (sIgE) measurements are used to help identify causative allergenic agents and to determine the degree of sensitization to facilitate treatment decisions. We examined the performance of a new third-generation chemiluminescent enzyme immunoassay for allergen-specific IgE (sIgE) on the continuous random access Immulite 2000 system.

METHODS

Detection limit and dilutional linearity were determined. Within-run and total precision were assessed according to the NCCLS EP5 guideline. Interlaboratory comparison of the new Immulite 2000 third-generation allergen-specific IgE assay was performed, as well as intermethod comparison against the Pharmacia FEIA, a second-generation assay.

RESULTS

The detection limit was <0.1 kU/l. Dilutional linearity held from 100 down to 0.2 kU/l. Regression analysis of the interlaboratory comparison results yielded: Immulite 2000(Laboratory 1)=1.07 Immulite 2000(Laboratory 2)+0.18 kU/l; r=0.98, n=3588 results. Intermethod comparison showed the following: Immulite 2000=0.83 (Pharmacia FEIA)+0.42 kU/l; r=0.79, n=512 results. Bland-Altman analysis of the interlaboratory and intermethod comparisons indicated no systematic bias.

CONCLUSIONS

We confirmed the reported performance characteristics of the third-generation sIgE assay and found reasonably good interlaboratory and intermethod agreement. The extended range capability of the third-generation assay provides a new tool for investigating cutoffs and trends in childhood allergy disease progression at concentrations <0.35 kU/l.

Comparison insight bone measurements by histomorphometry and microCT

Morphometric analysis of 70 bone biopsies was done in parallel by microCT and histomorphometry. microCT provided higher results for trabecular thickness and separation because of the 3D shape of these anatomical objects.

INTRODUCTION

Bone histomorphometry is used to explore the various metabolic bone diseases. The technique is done on microscopic 2D sections, and several methods have been proposed to extrapolate 2D measurements to the 3D dimension. X-ray microCT is a recently developed imaging tool to appreciate 3D architecture. Recently the use of 2D histomorphometric measurements have been shown to provide discordant results compared with 3D values obtained directly.

MATERIAL AND METHODS

Seventy human bone biopsies were removed from patients presenting with metabolic bone diseases. Complete bone biopsies were examined by microCT. Bone volume (BV/TV), Tb.Th, and Tb.Sp were measured on the 3D models. Tb.Th and Tb.Sp were measured by a method based on the sphere algorithm. In addition, six images were resliced and transferred to an image analyzer: bone volume and trabecular characteristics were measured after thresholding of the images. Bone cores were embedded undecalcified; histological sections were prepared and measured by routine histomorphometric methods providing another set of values for bone volume and trabecular characteristics. Comparison between the different methods was done by using regression analysis, Bland-Altman, Passing-Bablock, and Mountain plots.

RESULTS

Correlations between all parameters were highly significant, but microCT overestimated bone volume. The osteoid volume had no influence in this series. Overestimation may have been caused by a double threshold used in microCT, giving trabecular boundaries less well defined than on histological sections. Correlations between Tb.Th and Tb.Sp values obtained by 3D or 2D measurements were lower, and 3D analysis always overestimated thickness by approximately 50%. These increases could be attributed to the 3D shape of the object because the number of nodes and the size of the marrow cavities were correlated with 3D values.

CONCLUSION

In clinical practice, microCT seems to be an interesting method providing reliable morphometric results in less time than conventional histomorphometry. The correlation coefficient is not sufficient to study the agreement between techniques in histomorphometry. The architectural descriptors are influenced by the algorithms used in 3D.

Comparison of liquid chromatography-tandem mass spectrometry with a commercial enzyme-multiplied immunoassay for the determination of plasma MPA in renal transplant recipients and consequences for therapeutic drug monitoring

Mycophenolic acid (MPA) is an immunosuppressive drug partly metabolized to MPA-glucuronide (MPAG), which is pharmacologically inactive. The currently available enzyme-multiplied immunoassay technique (EMIT) has been reported to overestimate MPA plasma concentration in clinical samples when compared with HPLC techniques. The aims of this study were to design and validate a specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique for the determination of MPA and MPAG using a low plasma volume and a simple sample preparation procedure; then to compare it with EMIT for the determination of MPA in plasma samples collected over an interdose interval at different posttransplantation periods (days 3, 7, and 30 and after 3 months) in 25 renal transplant recipients orally administered cyclosporine and mycophenolate mofetil twice daily, to investigate the origins of the differences between techniques. The LC-MS/MS technique developed showed limits of quantification (LOQs) of 0.1 mg/L and 1 mg/L for MPA and MPAG, respectively, and was linear, accurate, and precise from these LOQs up to 30 mg/L for MPA and 300 mg/L for MPAG. EMIT gave similar results to LC-MS/MS for spiked quality control samples (in a synthetic matrix or in drug-free plasma) but significantly overestimated MPA levels in clinical samples: EMIT - LC-MS/MS = +61.39% +/- 57.94%, with large variations depending on patients, time elapsed since transplantation, sampling time, and concentration levels. These results confirmed the known overestimation of the EMIT assay compared with a specific method and showed that the magnitude of this overestimation depended on sampling time and time after transplantation.