How to use linear regression and correlation in quantitative method comparison studies

On topological indices and entropy measures of beryllonitrene network via logarithmic regression model

Chemical graph theory, a subfield of graph theory, is used to investigate chemical substances and their characteristics. Chemical graph analysis sheds light on the connection, symmetry, and reactivity of molecules. It supports chemical property prediction, research of molecular reactions, drug development, and understanding of molecular networks. A crucial part of computational chemistry is chemical graph theory, which helps researchers analyze and manipulate chemical structures using graph algorithms and mathematical models. Beryllonitrene , a compound of interest due to its potential applications in various fields, is examined through the lens of graph theory and mathematical modeling. The study involves the calculation and interpretation of topological indices and graph entropy measures, which provide valuable insights into the structural and energetic properties of Beryllonitrene's molecular graph. Logarithmic regression models are employed to establish correlations between these indices, entropy, and other relevant molecular attributes. The results contribute to a deeper understanding of Beryllonitrene's complex characteristics, facilitating its potential applications in diverse scientific and technological domains. In this study, degree-based topological indices TI are determined, as well as the entropy of graphs based on these TI .

Analyzing post-2000 groundwater level and rainfall changes in Rajasthan, India, using well observations and GRACE data

Research on groundwater and water resources is essential for preserving viable environments. Although the arid area has been identified as a significant hotspot for groundwater depletion, the Indian desert region was not included in the initial analysis. This study intends to evaluate Rajasthan's groundwater level (GWL) and rainfall trends from 2000 to 2021 and how variations in GWLs are related to long-term rainfall. Annual GWL and rainfall data time series were collected from 921 monitoring stations for 33 districts of Rajasthan. The GWL trends and rainfall were identified using non-parametric modified Mann-Kendall test and Spearman rho techniques. Pearson's, Kendall's (tau b), and Spearman's analyses were used to determine the correlation between GWL and rainfall. The results from the modified Mann-Kendall and Spearman rho methods reveal that GWL has a significant declining trend in 38 % of districts, where 13 % have no trend, and the rest of 49 % have a rising trend. The yearly rainfall trend at 70 % and 30 % of the districts are rising and stable, respectively. A negative correlation between GWL depth and rainfall was discovered in each district, where 15 % are firm, 58 % are moderate, and 27 % are weak negative correlations. Also, the regression analysis estimates the effect of rainfall on GWL, which was observed: rainfall negatively influenced the depth of GWL at 58 % of the districts, had a positive impact at 33 %, and others had no effect. GRACE TWS anomaly shows a decreasing trend of -1.22 cm/yr, and GRACE and GWL anomalies have a positive relationship (r = 0.471). Results conclude that rainfall is the primary influencer on GWL in this semi-arid region vulnerable to drought.

Determination of Minerals in Soft and Hard Cheese Varieties by ICP-OES: A Comparison of Digestion Methods

For sample preparation prior to mineral analysis, microwave digestion (~2 h) is quicker and requires lower acid volume as compared to dry (6-8 h) and wet digestion (4-5 h). However, microwave digestion had not yet been compared systematically with dry and wet digestion for different cheese matrices. In this work, the three digestion methods were compared for measuring major (Ca, K, Mg, Na and P) and trace minerals (Cu, Fe, Mn and Zn) in cheese samples using inductively coupled plasma optical emission spectrometry (ICP-OES). The study involved nine different cheese samples with moisture content varying from 32 to 81% and a standard reference material (skim milk powder). For the standard reference material, the relative standard deviation was lowest for microwave digestion (0.2-3.7%) followed by dry (0.2-6.7%) and wet digestion (0.4-7.6%). Overall, for major minerals in cheese, strong correlation was observed between the microwave and the dry and wet digestion methods (R² = 0.971-0.999), and Bland-Altman plots showed best method agreement (lowest bias), indicating the comparability of all three digestion methods. A lower correlation coefficient, higher limits of agreement and higher bias of minor minerals indicate possibilities of measurement error.

Are basic laboratory skills adequately acquired by undergraduate science students? How control quality methodologies applied to laboratory lessons may help us to find the answer

Graphical abstract

A systematic review of the validity, reliability, and feasibility of measurement tools used to assess the physical activity and sedentary behaviour of pre-school aged children

Physical activity (PA) and sedentary behaviour (SB) of pre-school aged children are associated with important health and developmental outcomes. Accurate measurement of these behaviours in young children is critical for research and practice in this area. The aim of this review was to examine the validity, reliability, and feasibility of measurement tools used to assess PA and SB of pre-school aged children.Searches of electronic databases, and manual searching, were conducted to identify articles that examined the measurement properties (validity, reliability or feasibility) of measurement tools used to examine PA and/or SB of pre-school aged children (3-7 years old). Following screening, data were extracted and risk of bias assessment completed on all included articles.A total of 69 articles, describing 75 individual studies were included. Studies assessed measurement tools for PA (n = 27), SB (n = 5), and both PA and SB (n = 43). Outcome measures of PA and SB differed between studies (e.g. moderate to vigorous activity, step count, posture allocation). Most studies examined the measurement properties of one measurement tool only (n = 65). Measurement tools examined included: calorimetry, direct observation, combined heart rate and accelerometry, heart rate monitors, accelerometers, pedometers, and proxy report (parent, carer or teacher reported) measures (questionnaires or diaries). Studies most frequently assessed the validity (criterion and convergent) (n = 65), face and content validity (n = 2), test-retest reliability (n = 10) and intra-instrument reliability (n = 1) of the measurement tools. Feasibility data was abstracted from 41 studies.Multiple measurement tools used to measure PA and SB in pre-school aged children showed some degree of validity, reliability and feasibility, but often for different purposes. Accelerometers, including the Actigraph (in particular GT3X versions), Actical, ActivPAL and Fitbit (Flex and Zip), and proxy reported measurement tools used in combination may be useful for a range of outcome measures, to measure intensity alongside contextual information.

Validation of quantitative gait analysis systems for Parkinson's disease for use in supervised and unsupervised environments

BACKGROUND

Gait impairments are among the most common and impactful symptoms of Parkinson's disease (PD). Recent technological advances aim to quantify these impairments using low-cost wearable systems for use in either supervised clinical consultations or long-term unsupervised monitoring of gait in ecological environments. However, very few of these wearable systems have been validated comparatively to a criterion of established validity.

OBJECTIVE

We developed two movement analysis solutions (3D full-body kinematics based on inertial sensors, and a smartphone application) in which validity was assessed versus the optoelectronic criterion in a population of PD patients.

METHODS

Nineteen subjects with PD (7 female) participated in the study (age: 62 ± 12.27 years; disease duration: 6.39 ± 3.70 years; HY: 2 ± 0.23). Each participant underwent a gait analysis whilst barefoot, at a self-selected speed, for a distance of 3 times 10 m in a straight line, assessed simultaneously with all three systems.

RESULTS

Our results show excellent agreement between either solution and the optoelectronic criterion. Both systems differentiate between PD patients and healthy controls, and between PD patients in ON or OFF medication states (normal difference distributions pooled from published research in PD patients in ON and OFF states that included an age-matched healthy control group). Fair to high waveform similarity and mean absolute errors below the mean relative orientation accuracy of the equipment were found when comparing the angular kinematics between the full-body inertial sensor-based system and the optoelectronic criterion.

CONCLUSIONS

We conclude that the presented solutions produce accurate results and can capture clinically relevant parameters using commodity wearable sensors or a simple smartphone. This validation will hopefully enable the adoption of these systems for supervised and unsupervised gait analysis in clinical practice and clinical trials.

Effects of GSTT1 Genotype on the Detoxification of 1,3-Butadiene Derived Diepoxide and Formation of Promutagenic DNA-DNA Cross-Links in Human Hapmap Cell Lines

Smoking is a leading cause of lung cancer, accounting for 81% of lung cancer cases. Tobacco smoke contains over 5000 compounds, of which more than 70 have been classified as human carcinogens. Of the many tobacco smoke constituents, 1,3-butadiene (BD) has a high cancer risk index due to its tumorigenic potency and its abundance in cigarette smoke. The carcinogenicity of BD has been attributed to the formation of several epoxide metabolites, of which 1,2,3,4-diepoxybutane (DEB) is the most toxic and mutagenic. DEB is formed by two oxidation reactions carried out by cytochrome P450 monooxygenases, mainly CYP2E1. Glutathione-S-transferase theta 1 (GSTT1) facilitates the conjugation of DEB to glutathione as the first step of its detoxification and subsequent elimination via the mercapturic acid pathway. Human biomonitoring studies have revealed a strong association between GSTT1 copy number and urinary concentrations of BD-mercapturic acids, suggesting that it plays an important role in the metabolism of BD. To determine the extent that GSTT1 genotype affects the susceptibility of individuals to the toxic and genotoxic properties of DEB, GSTT1 negative and GSTT1 positive HapMap lymphoblastoid cell lines were treated with DEB, and the extent of apoptosis and micronuclei (MN) formation was assessed. These toxicological end points were compared to the formation of DEB-GSH conjugates and 1,4-bis-(guan-7-yl)-2,3-butanediol (bis-N7G-BD) DNA-DNA cross-links. GSTT1 negative cell lines were more sensitive to DEB-induced apoptosis as compared to GSTT1 positive cell lines. Consistent with the protective effect of GSH conjugation against DEB-derived apoptosis, GSTT1 positive cell lines formed significantly more DEB-GSH conjugate than GSTT1 negative cell lines. However, GSTT1 genotype did not affect formation of MN or bis-N7G-BD cross-links. These results indicate that GSTT1 genotype significantly influences BD metabolism and acute toxicity.

Assessment of a dried blood spot C-reactive protein method to identify disease flares in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is characterised by painful, stiff and swollen joints. RA features sporadic 'flares' or inflammatory episodes-mostly occurring outside clinics-where symptoms worsen and plasma C-reactive protein (CRP) becomes elevated. Poor control of inflammation results in higher rates of irreversible joint damage, increased disability, and poorer quality of life. Flares need to be accurately identified and managed. A method comparison study was designed to assess agreement between CRP values obtained by dried blood spot (DBS) versus conventional venepuncture sampling. The ability of a weekly DBS sampling and CRP test regime to detect flare outside the clinic was also assessed. Matched venepuncture and finger lancet DBS samples were collected from n = 100 RA patients with active disease at baseline and 6 weeks (NCT02809547). A subset of n = 30 RA patients submitted weekly DBS samples over the study period. Patient demographics, including self-reported flares were recorded. DBS sample CRP measurements were made by enzyme-linked immunosorbent assay, and venepuncture samples by a reference immunoturbometric assay. Data was compared between sample types by Bland-Altman and weighted Deming regression analyses. Flare detection sensitivity and specificity were compared between 'minimal' baseline and 6 week sample CRP data and the 'continuous' weekly CRP data. Baseline DBS ELISA assay CRP measures yielded a mean positive bias of 2.693 ± 8.640 (95% limits of agreement - 14.24 to 19.63%), when compared to reference assay data. Deming regression revealed good agreement between the DBS ELISA method and reference assay data, with baseline data slope of 0.978 and intercept -0.153. The specificity of 'continuous' area under the curve (AUC) CRP data (72.7%) to identify flares, was greater than 'minimal' AUC CRP data (54.5%). This study indicates reasonable agreement between DBS and the reference method, especially at low to mid-range CRP values. Importantly, longitudinal CRP measurement in RA patients helps to clearly identify flare and thus could assist in remote monitoring strategies and may facilitate timely therapeutic intervention.Trial registration: The Remote Arthritis Disease Activity MonitoR (RADAR) study was registered on 22/06/2016 at ClinicalTrials.gov Identifier: NCT02809547. https://clinicaltrials.gov/ct2/show/NCT02809547 .

Interpretation and Implications of Lognormal Linear Regression Used for Bacterial Enumeration

Background

Bacterial enumeration data are typically log transformed to realize a more normal distribution and stabilize the variance. Unfortunately, statistical results from log transformed data are often misinterpreted as data within the arithmetic domain.

Objective

To explore the implication of slope and intercept from an unweighted linear regression and compare it to the results of the regression of log transformed data.

Method

Mathematical formulae inferencing explained using real dataset.

Results

For y=Ax+B+ε, where y is the recovery (CFU/g) and x is the target concentration (CFU/g) with error ε homogeneous across x. When B=0, slope A estimates percent recovery R. In the regression of log transformed data, logy=αlogx+β+εz (equivalent to equation y=Axα·ω), it is the intercept β=logyx=logA that estimates the percent recovery in logarithm when slope α=1, which means that R doesn’t vary over x. Error term ω is multiplicative to x, while εz or log(ω) is additive to log(x). Whether the data should be transformed or not is not a choice, but a decision based on the distribution of the data. Significant difference was not found between the five models (the linear regression of log transformed data, three generalized linear models and a nonlinear model) regarding their predicted percent recovery when applied to our data. An acceptable regression model should result in approximately the best normal distribution of residuals.

Conclusions

Statistical procedures making use of log transformed data should be studied separately and documented as such, not collectively reported and interpreted with results studied in arithmetic domain.

Highlights

The way to interpret statistical results developed from arithmetic domain does not apply to that of the log transformed data.

Evaluation of the Reticulocyte Production Index in the Pediatric Population

OBJECTIVES

Since hematologic values vary with age in children, we evaluated the agreement between the "traditional" reticulocyte production index (RPI) and an RPI by age (RPI/A)-adjusted normal values.

METHODS

A retrospective, observational, and analytical study was performed on CBCs of children with anemia younger than 18 years. The agreement and clinical repercussions of the RPI values were analyzed with an RPI/A developed with theoretical values for different ages.

RESULTS

A total of 5,503 tests were analyzed and no systematic error between the two indices was found; however, there were significant proportional differences at higher values that resulted in lower RPI/A in children younger than 15 days and higher RPI/A in children aged 15 days and older. No agreement was observed at any age. The proportion of arregenerative anemia diagnosed using RPI/A was higher in children younger than 15 days and lower in those 15 days and older.

CONCLUSIONS

RPI is not an adequate tool for evaluating the erythropoietic capacity of bone marrow in the pediatric population. The disagreement between the results can be explained by the difference in normal hematologic values between children and adults.

Maneuver-Based Objectification of User Comfort Affecting Aspects of Driving Style of Autonomous Vehicle Concepts

Driving maneuvers try to objectify user needs regarding the driving dynamics for a vehicle concept. As autonomous vehicles will not be driven by people, the driving style that merges the individual aspects of driving dynamics, like user comfort, will be part of the vehicle concept itself. New driving maneuvers are, therefore, necessary to objectify the driving style of autonomous vehicle concepts with all its interdependencies relating to the individual aspects. This paper presents a methodology to design such driving maneuvers and includes a pilot study and a user study. As an example, the methodology was applied to the parameters of user comfort and travel time. The driven maneuvers resulted in statistical equations to objectify the interdependencies of these two aspects. Finally, this paper provides an outlook for needed maneuvers in order to tackle the entire driving style with its multidimensional facets.

Comparative Analysis of Protein Quantification Methods for the Rapid Determination of Protein Loading in Liposomal Formulations

Advances in manufacturing processes provide the ability for the high throughput production of liposomes containing a range of moieties, from small molecules to large biologicals (including proteins and nucleic acids for prophylactic and therapeutic applications). Whilst rapid quantification methods for small molecules are generally well established, the ability to rapidly quantify liposomal entrapment of proteins is limited. Indeed, most standard protein quantification techniques (including the BCA assay and Reverse phase-high performance liquid chromatography (RP-HPLC)) measure protein encapsulation indirectly, by measuring the amount of non-incorporated drug, and subtracting from the initial amount of protein added. However, this can give inaccurate and misrepresentative results. To address this, we have developed a range of methods to directly quantify protein entrapment within liposomes. The encapsulation efficiency within neutral, anionic and cationic liposome formulations was determined by three techniques; BCA assay, RP-HPLC and HPLC coupled to an evaporative light scattering detector, (HPLC-ELSD). All three methods are reliable for the quantification of protein, with linear responses and correlation coefficients of 0.99, and LOQ for all three methods being less than 10 µg/mL. Here within, we provide three methods for the rapid and robust quantification of protein loading within liposomal (and other bilayer) vesicle systems.

Comparison of central venous saturation by standard ABG machine versus co-oximeter: Is 18 carat as good as the 24 carat gold standard?

AIMS

Aggressive therapy aimed at desired end-points of Early Goal Directed Therapy (EGDT) is the cornerstone of septic shock management. A key endpoint that improves outcomes is achieving central venous saturation (ScvO2) >70%. The gold standard to measure ScvO2 is by a co-oximeter (co-ox).

SETTINGS AND DESIGN

This prospective, observational study from a multidisciplinary pediatric intensive care unit (PICU) was conducted to assess the validity of ScvO2 levels by standard ABG (stand ABG) machine in comparison with co-ox in conditions that shifted the oxygen dissociation curve (ODC) to the right or left in sick children and controls.

MATERIALS AND METHODS

Data from paired samples was tested for correlation coefficient for pH, paCO2, paO2, and ScvO2. Tests for correlation (Pearson's coefficient) and agreement (Bland-Altman analysis) were performed on ScvO2 values obtained in various subgroups. Sensitivity and specificity for ScvO2 values determined by standard ABG machine versus co-ox were calculated in reference to EGDT endpoints.

RESULTS

A total of 141 paired samples were collected from 82 children. Despite a statistically significant difference in the pH and ScvO2, there was good linear correlation between these parameters. Limits of agreement between ScvO2 measured by standard ABG machine and co-ox by Bland-Altman gave 2.3% bias with 95% CI of -24.2% to 19.5%. Sensitivity and specificity of standard ABG machine in detecting low ScvO2 in shock was 84.21% and 93.18% respectively, while it was false positive in 4 samples.

CONCLUSIONS

The less expensive standard ABG machine showed satisfactory correlation with gold standard co-ox over a range of patient conditions; however, the wide range for agreement was of concern and it performed particularly poorly in anemic patients.

Challenges in implementing clinical liquid chromatography-tandem mass spectrometry methods--the light at the end of the tunnel

The use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the clinical setting is a relatively new application. One of the significant barriers hampering the transition of LC-MS/MS from the research lab into a clinical setting is the uncertainty of how to successfully develop and validate a method that meets guidelines for clinical applications. Here, we have taken this seemingly overwhelming process and broken it into five general stages for consideration: assessing the clinical validity of a new LC-MS/MS assay, determination of feasibility, assay development, assay validation and post-implementation monitoring. Although various publications are available and serve as resources for determining development processes and acceptability criteria for specific LC-MS/MS assays, many of them are general recommendations or are specific to research applications that may not translate either practically or clinically. In this perspective special feature article, a resource is compiled that describes key differences between LC-MS/MS methods for research use versus clinical use. In addition, the challenges facing the expanding role of this technique in the clinical setting are discussed, including instrumentation/automation challenges, potential regulation of laboratory developed tests by the US Food and Drug Administration and standardization and harmonization of MS methods through the use of traceable materials and availability of guidance documents.

Objective assessment of learning curves for the Voxel-Man TempoSurg temporal bone surgery computer simulator

Introduction:

Simulators are becoming an increasingly important part of surgical training. Temporal bone surgery is one area in which simulators, such as the Voxel-Man TempoSurg simulator, are likely to play a significant role in training. We present learning curve data from novice trainees using this simulator to learn cortical mastoidectomy, exposure of the sigmoid sinus, and exposure of the short process of the incus.

Methods:

We measured the time taken to perform the procedures, the volume of reference bone removed, and the structures damaged during dissection.

Results:

We found improvement in a number of parameters over the course of the study. The overall scores, structural damage scores and time taken improved, to differing degrees, for each task. The volume of reference bone removed remained constant.

Conclusion:

These results indicate that the trainees' efficiency improved as they became more proficient at removing a given volume of reference bone.

Biomarkers of dementia: comparison of electrochemiluminescence results and reference ranges with conventional ELISA

We compared the performance of the Meso Scale Diagnostics electrochemiluminescence (MSD) multiplex assay for t-tau and p-tau(231), originally developed for measurement of brain cell extract and tissue cultures, with the established standard method, the Innogenetics ELISA for total and p-tau(181). The methods were also clinically evaluated with 120 samples from our mono center population. The established Innogenetics ELISA procedures have been well optimized to measure patient samples in the normal and pathological range. Compared to the MSD they were superior in the limit of detection for total as well as p-tau. The obtained reference values for our normal controls were in the upper third of the published studies. Innogenetics tau, Innogenetics p-tau(181) and MSD t-tau differentiated the Alzheimer's (n=44) and minimal impairment group (MCI, n=39) from normal controls (n=37), but the MCI group was not statistically different from the normal controls. The MSD multiplex assay measured t-tau adequately but p-tau(231) could not differentiate normal from pathological results in CSF due to the high limit of detection. Both procedures however, have to be further standardized and complemented by adequate internal and external quality control schemes to qualify for routine analysis in a medical laboratory.

Comparison of an antibody capture and a cell capture ligand-binding assay to quantify a monoclonal therapeutic in serum

Background: Ligand-binding assays are a tool used for the quantification of antibody therapies. When assay format changes are required during the drug development process it is advisable to assess these formats ensuring the resulting data can be compared. In this article, we outline the method and results obtained comparing an anti-idiotype capture and a cell-capture ligand-binding assay. Results: Comparison of results for all quality controls between assays were within acceptance limits, with the exception of the low quality control. Statistical analysis of the results demonstrated 95% power to detect a 20% difference between data sets. Subsequent analysis of unknown samples further confirmed 98% power to detect a 20% difference between data sets. Conclusion: Results obtained using two assay formats are statistically comparable to each other.

Quantitative recovery of proviral HIV-1 DNA from leukocytes by the Dried Buffy Coat Spot method for real-time PCR determination

The current recommended method for diagnosing HIV-1 in newborns infected vertically and in adults, during the "window period", is the detection of proviral HIV-1 DNA within leukocytes (buffy coat). This study describes a new portable Dried Buffy Coat Spot (DBCS) assay able to provide a quantitative proviral HIV-1 DNA recovery from the buffy coat. Fifty blood samples were collected from HIV-positive children and processed for DBCSs. Total DNA and proviral DNA were normalised to β-globin and HIV-1 pol genes. Assay sensitivity and specificity were evaluated against the whole blood dried blood spot (DBS) method. Both procedures, using automatic DNA extraction, were compared to a standard whole blood DNA manual extraction. DNA recovery from whole blood was nearly equivalent to that of the DBCS-based extraction, while DBS-based extraction was 10-fold less sensitive. The detection rate of proviral HIV-1 DNA with DBCS assay was equivalent to whole blood manual extraction (100% concordance), but DBS-extracted samples showed limited concordance (44%). The DBCS assay may prove to be more feasible in resource-limited settings. It may represent a simple and robust point-of-care assay for HIV screening of children, for whom a reference test is still lacking.

Investigation of outpatients referred to a chemical pathologist with potential pseudohyperkalaemia

Background:

Pseudohyperkalaemia is when the in vitro blood potassium concentration is artefactually raised while the in vivo concentration is normal. With unexplained hyperkalaemia, pseudohyperkalaemia needs to be excluded to avoid unnecessary and potentially detrimental therapy. There are numerous causes, but no systematic approach for the investigation of outpatients with potential pseudohyperkalaemia exists in the literature.

Aims:

To evaluate the in-house protocol.

Methods:

Patients referred for investigation of potential pseudohyperkalaemia underwent an outpatient based protocol which is designed to determine whether the cause was due to delayed blood separation, clotting, centrifugation or a haematological abnormality.

Results:

32 patients with serum potassium of 5.5–7.1 mmol/l were referred. All patients had pseudohyperkalaemia; the most frequent causes were full blood count (FBC) abnormalities (28%), time >4 hours from sampling to centrifugation (28%) and sample clotting (25%). Anaemia was more likely to be found in male patients.

Conclusion:

Before a problem can be treated, it must be confirmed and its aetiology identified. A systematic approach to investigate potential pseudohyperkalaemia has been presented. This confirmed the clinician’s suspicion of pseudohyperkalaemia and in the majority of patients the aetiology was also identified. The use of serum and plasma potassium with an FBC in the initial investigation will identify whether clotting or a haematological abnormality is the cause in about half of the cases. Assay of whole-blood potassium is less important as centrifugation is a rare cause. Time to centrifugation is likely to play a major part in the majority of the remaining cases.

Comparison of Immunoassays for the Selective Measurement of Human High–Molecular Weight Adiponectin

Background: Adiponectin is an adipocyte-derived hormone circulating in different multimer complexes. The high–molecular-weight (HMW) complex is likely the active form of this protein and has been recognized as a risk marker for type 2 diabetes and coronary artery disease (CAD). Because quantification of HMW adiponectin by Western blot analysis is time-consuming, novel ELISAs have been developed to simplify measurements in clinical research. However, these enzyme immunoassays have not been cross-validated in larger patient groups. We evaluated 2 individual ELISA systems by comparison to Western blotting for measurement of the distribution of HMW adiponectin in healthy individuals and patients with CAD and type 2 diabetes.

Methods: We measured HMW adiponectin in 204 individuals (83 CAD patients, 81 type 2 diabetes patients, and 40 healthy controls). Correlations, range of agreement, and imprecision of HMW concentrations obtained using 2 commercial ELISAs (#1, ALPCO Diagnostics; #2, Millipore) were evaluated by comparison with quantitative Western blotting.

Result: Adiponectin results of the ELISAs were significantly correlated with those obtained by Western blotting (both r > 0.75, P < 0.001). Deming regression and Bland-Altman analyses indicated high agreement among the 3 immunoassays. The median difference between HMW adiponectin concentrations measured by ELISA and by Western blot was +0.4 mg/L for ELISA #1 and −0.4 mg/L for ELISA #2 with 95% of value differences <3 mg/L.

Conclusions: Selective measurement of HMW adiponectin by ELISA is feasible; however, individual differences among immunoassays must be considered. The evaluated ELISAs exhibit analytical characteristics that allow their use as equivalent for Western blot analysis in larger clinical and epidemiological groups.

Derivation and internal validation of an equation for albumin-adjusted calcium

BACKGROUND

Previously published equations to adjust calcium for albumin concentration may vary depending on factors such as the type of reagents used. Albumin-adjusted calcium equations derived from laboratories using the bromocresol purple (BCP) albumin binding reagent have not been described.

METHODS

The linear regression equation for the binding of calcium and BCP-albumin was derived in a cohort of 4613 outpatients, and the albumin-adjusted calcium equation was internally validated in a separate cohort of 1538 subjects. The performance of this equation was compared with a previously published equation (adjusted [Ca](mmol/L) = total [Ca](mmol/L) + 0.02 (40 - [albumin] (g/L)) in 343 subjects with albumin < 33 g/L (below reference range).

RESULTS

The local adjustment equation was expressed by the relationship; adjusted [Ca](mmol/L) = total [Ca](mmol/L) + 0.012 (39.9 - [albumin](g/L)). The equation showed evidence of good internal validity (shrinkage value of adjusted r2 = -0.0059). Classification of calcium status differed between the two equations in 47 of 343 subjects with low serum albumin (weighted kappa = 0.46; moderate agreement).

CONCLUSION

A locally derived and internally validated albumin-adjusted calcium equation differed from previously published equations and resulted in important differences in classification of calcium status in hypoalbuminemia patients. Individual laboratories should determine their own linear regression equation for calcium on albumin rather than relying on published formulas.