bluuebunny/crossref_metadata_2025_split huggingface dataset:
Is serum cystatin C the marker of choice to predict glomerular filtration rate in paediatric patients?
Authors: Willems Hans L. , Hilbrands Luuk B. , van de Calseyde John F. , Monnens Leo A.H. , Swinkels Dorine W. 
Published: January 2003

Background: It has been suggested that serum cystatin C (cyst-C) concentration provides a better indication of changes in glomerular filtration rate (GFR) than does serum creatinine concentration. Methods: Because of conflicting results as to the usefulness of cyst-C, we compared the GFRs calculated from serum cyst-C, inulin clearance and endogenous creatinine clearance in children. GFRs calculated from cystatin concentration, inulin clearance following a single injection and endogenous creatinine clearance using Jaffé and enzymic methods were compared in 66 children (1·3-21·9 years) with a variety of renal disorders. Receiver operating curve analysis was used to determine the cut-off value that would give the best discrimination between normal and decreased GFR. Results: The serum cyst-C concentration ranged from 0·66 to 7·61 mg/L (median 1·94). Serum creatinine Jaffé concentration (creat-J) ranged from 38 to 871 µmol/L (median 105) and creatinine enzymatic concentration (creat-E) ranged from 28 to 862 µmol/L (median 126). The linear correlation coefficient ( R) of 1/cyst-C versus GFR ( R = 0·937) did not differ from either that of 1/creat-J versus GFR ( R = 0·918) or that of 1/creat-E versus GFR ( R = 0·901). These coefficients had overlapping confidence intervals. The areas under the curve for cyst-C, creat-J and creat-E were 0·967, 0·977 and 0·924, respectively, and were not significantly different from each other. For cyst-C, the optimal cut-off was 1·1 mg/L. Conclusions: Serum cyst-C is equivalent to creat-J and creat-E as a marker for estimating the GFR in the paediatric population studied.
Cobalamin-binding proteins in normal and cobalamin-deficient older subjects
Authors: van Asselt Dieneke Z.B. , Thomas Chris M.G. , Segers Martin F.G. , Blom Henk J. , Wevers Ron A. , Hoefnagels Willibrord H.L. 
Published: January 2003

Background: The causes of cobalamin (vitamin B12) deficiency in older people are only partly understood. We investigated the role of the cobalamin-binding proteins and tested the hypothesis that low saturated transcobalamin concentration is an early marker of cobalamin deficiency. Methods: We measured saturated (holo) and unsaturated (apo) transcobalamin and haptocorrin concentrations in healthy middle-aged volunteers, healthy older volunteers, cobalamin-deficient older volunteers and cobalamin-deficient older patients. Results: Holo and apo concentrations of transcobalamin and haptocorrin were similar in healthy middle-aged and older subjects. Holotranscobalamin concentrations were significantly decreased in cobalamin-deficient subjects but did not differ between healthy volunteers and patients. Furthermore, the relative amount of cobalamin on transcobalamin (i.e. holotranscobalamin/holotranscobalamin + holohaptocorrin) was similar in all four groups. Conclusions: Abnormalities of the cobalamin-binding proteins are not a cause of cobalamin deficiency in the aged. Plasma holotranscobalamin concentration did not differ between stages of cobalamin deficiency in older persons. Therefore, plasma holotranscobalamin is not an early marker of cobalamin deficiency in older people and has no additional value in the diagnostic work-up of reduced plasma cobalamin concentrations in older people.
Combination therapy in childhood leukaemia: in vitro studies of thiopurines and inhibitors of purine metabolism on apoptosis
Authors: De Abreu Ronney A. , Trueworthy Robert C. , van Kuilenburg André B.P. , Vogels-Mentink Trude M. , Lambooy Lambert H.J. , van Gennip Albert H. 
Published: January 2003

Background: Methotrexate (MTX) followed by 6-mercaptopurine (6MP) is one of the best known combinations for the treatment of childhood acute lymphoblastic leukaemia. Tiazofurin (TF) and 6-thioguanine (TG) are also used as chemotherapy agents in the treatment of malignancies. We have examined the induction of apoptosis by combinations of these drugs to gain more insights into their efficacy in the treatment of malignancies. Methods: The induction of apoptosis was examined in Molt-4, a human malignant acute lymphoblastic T-cell line. The cells were exposed to increasing drug concentrations at various exposure times. Annexin V/FITC and propidium iodide (PI) were used as markers for apoptosis and cell death. Annexin V/FITC positive and PI positive cells were detected by flow-cytometric analysis. Results: Sequential 24-h exposure with MTX (0·005-0·02 µmol) followed by 6MP (1-10 µmol) and 24-h exposure with TF (5·20 µmol) followed by TG (0·5-2 µmol) showed a more than additive induction of apoptosis compared with single-drug exposure. Simultaneous administration of the drugs does not show an additive effect on apoptosis. Conclusions: The results of this study indicate that sequential administration of MTX before 6MP and of TF before TG may be essential for therapeutic success in the treatment of leukaemia.
An improved procedure for testing for assay linearity
Authors: Ross H.A. , Sweep C.G.J. 
Published: January 2003

Background: Statistical testing of assay linearity using replicate measurements made on binary mixtures of samples provides no information about the significance of any detected deviations from linearity, which may often be desirable. Method: Performance of additional statistical analysis of the assay data. Result: Objective measures for non-linearity and the minimum detectable deviation from linearity of the assay are obtained. Conclusion: A few additional calculations from the available data make it possible to assess whether or not an assay method needs improvement to achieve adequate performance within its intended application.
Kinetics of myo-inositol loading in women of reproductive age
Authors: Groenen Pascal M.W. , Merkus Hans M.W.M. , Sweep Fred C.G.J. , Wevers Ron A. , Janssen Fokje S.M. , Steegers-Theunissen Régine P.M. 
Published: January 2003

Background: Myo-inositol plays a key role in an important intracellular signalling pathway. A deranged myo-inositol metabolism has been associated with neural tube defects. A myo-inositol loading test was performed to investigate the kinetics in healthy women of reproductive age. Methods: Five healthy non-obese females {mean age (standard deviation: SD) 22·8 (2·2) years} were recruited at the University Medical Center Nijmegen. Blood samples were drawn fasting and at 20, 40, 60, 90, 180 and 270 min after ingestion of 100 mg/kg body weight of myo-inositol. Urine samples were collected before myo-inositol loading and at 180 and 270 min post-loading. Samples were analysed for serum myo-, epi- and scyllo-inositol and glucose concentrations by gas chromatography. Plasma insulin concentrations were determined by radio-immunoassay. Random intercept models were fitted to evaluate the data. Results: The estimated myo-inositol and scyllo-inositol concentrations both reached maximum values at 180 min post-loading, respectively: mean (SD) 101·5 (9·2) µmol/L and 1·09 (0·11) µmol/L. The estimated plasma insulin and serum glucose concentrations decreased slightly but significantly during the experiment: P < 0·0001 and P < 0·05, respectively. At 180 and 270 min post-loading, urinary myo-inositol concentrations were increased and urinary glucose concentrations were unchanged. Conclusions: Myo-inositol enters the bloodstream quickly after oral ingestion and a small amount of myo-inositol is converted to scyllo-inositol. The synthesis of glucose from myo-inositol could not be detected by serum measurements. These data can be used in further research into the association between myo-inositol and neural tube defects.
Measurement of thiopurine S-methyltransferase activity in human blood samples based on high-performance liquid chromatography: reference values in erythrocytes from children
Authors: Keizer-Garritsen Jenneke J. , Brouwer Connie , Lambooy Lambert H.J. , Ter Riet Patricia , Bökkerink Jos P.M. , Trijbels Frans J.M. , De Abreu Ronney A. 
Published: January 2003

Background: Monitoring 6-thiopurine S-methyltransferase (TPMT; EC 2.1.1.67) activity is especially important when patients are treated with 6-thiopurine drugs, since severe bone marrow toxicity may be induced if patients have deficient TPMT activity. Methods: We have developed a method based on high-performance liquid chromatography (HPLC) for the measurement of TPMT activity in various cell types: erythrocytes (RBC), human peripheral blood mononuclear cells (pMNC) and human malignant lymphoblasts (Molt-F4). The enzymatic activity is measured by the amount of 6-methylmercaptopurine formed, using 6-mercaptopurine (6MP) as substrate and S-adenosylmethionine as co-substrate. Results: The Km values calculated for 6MP were 0·54 (RBC), 0·85 (pMNC) and 0·65 (Molt-F4 cells) mmol/L. The Km values for S-adenosylmethionine were 11·9 (RBC), 16·4 (pMNC) and 6·65 (Molt-F4 cells) µmol/L. The assay variation was 8·2-17%. TPMT activity was determined in a control group of 103 children and young adults (44 female, 59 male). The values observed were (mean ± standard deviation): female children and young adults, 15·1 ± 4·8 pmol/107 cells per h ( n = 44); male children and young adults, 15·8 ± 6·4 pmol/107 cells per h ( n = 59). No gender or age differences were found. Conclusion: The HPLC-based method enables the rapid screening of TPMT activities in large groups of patients treated with 6-thiopurines.
Quantitative detection of peripheral thyroglobulin mRNA has limited clinical value in the follow-up of thyroid cancer patients
Authors: Span P.N. , Sleegers M.J.M. , van den Broek W.J. , Ross H.A. , Nieuwlaat W-A. , Hermus A.R.M.M. , Sweep C.G.J. 
Published: January 2003

Background: As recurrences after treatment for differentiated thyroid cancer can occur many years after thyroidectomy, periodic monitoring of serum thyroglobulin (Tg) levels is performed in these patients. However, autoantibodies that can interfere with Tg immunoassays occur in the blood of approximately 25% of these patients. Several earlier reports suggest that measuring Tg mRNA by reverse-transcriptase polymerase chain reaction (RT-PCR) could be of value, especially in patients with Tg autoantibodies. Methods: Using an earlier described, real-time quantitative Taqman RT-PCR assay, Tg mRNA concentrations were assessed in peripheral blood taken from 58 patients treated for thyroid cancer and from two healthy controls. Results: In all tested samples Tg mRNA could be found. No correlation between serum Tg protein and Tg mRNA could be found. Tg mRNA concentrations did not differ between serum Tg-negative and Tg-positive patients. No differences in the number of patients with high or low Tg/ β-actin ratios were found between the groups of patients without, 131I uptake on whole-body scan, or patients with thyroid bed uptake, uptake elsewhere in the neck, or distant metastases with or without regional uptake ( P = 0·871). Conclusions: We were not able to confirm earlier positive reports on the clinical value of Tg mRNA measurement for the monitoring of patients treated for thyroid cancer.
Stability studies of ubiquinol in plasma
Authors: Hectors M.P.C. , van Tits L.J.H. , de Rijke Y.B. , Demacker P.N.M. 
Published: January 2003

Background: Ubiquinol is a sensitive redox marker in the first line of the antioxidative defence mechanism and is increasingly being measured in oxidation studies. Because of its apparent instability during storage and processing, we compared various storage conditions. Method: Blood was collected from three volunteers into tubes containing EDTA; it was then separated at 4°C and cryopreserved with saccharose (final concentration 6 g/L). Aliquots were stored with or without glutathione or butylated hydroxytoluene at -20°C and -80°C. Results and conclusion: Ubiquinol in samples stored at -20°C was not stable; however, it was stable when stored at -80°C, even without addition of antioxidant. By contrast, α-tocopherol was stable under all conditions studied.
Web Site Usability, Design, and Performance Metrics
Authors: Palmer Jonathan W. 
Published: January 2003

Web sites provide the key interface for consumer use of the Internet. This research reports on a series of three studies that developand validate Web site usability, design and performance metrics, including download delay, navigability, site content, interactivity, and responsiveness. The performance metric that was developed includes the subconstructs user satisfaction, the likelihood of return, and the frequency of use. Data was collected in 1997, 1999, and 2000 from corporate Web sites via three methods, namely, a jury, third-party ratings, and a software agent. Significant associations between Web site design elements and Web site performance indicate that the constructs demonstrate good nomological validity. Together, the three studies provide a set of measures with acceptable validity and reliability. The findings also suggest lack of significant common methods biases across the jury-collected data, third-party data, and agent-collected data. Results suggest that Web site success is a first-order construct. Moreover, Web site success is significantly associated with Web site download delay (speed of access and display rate within the Web site), navigation (organization, arrangement, layout, and sequencing), content (amount and variety of product information), interactivity (customization and interactivity), and responsiveness (feedback options and FAQs).
Assessing a Firm's Web Presence: A Heuristic Evaluation Procedure for the Measurement of Usability
Authors: Agarwal Ritu , Venkatesh Viswanath 
Published: January 2003

Web site usability is a critical metric for assessing the quality of a firm's Web presence. A measure of usability must not only provide a global rating for a specific Web site, ideally it should also illuminate specific strengths and weaknesses associated with site design. In this paper, we describe a heuristic evaluation procedure for examining the usability of Web sites. The procedure utilizes a comprehensive set of usability guidelines developed by Microsoft. We present the categories and subcategories comprising these guidelines, and 7discuss the development of an instrument that operationalizes the measurement of usability. The proposed instrument was tested in a heuristic evaluation study where 1,475 users rated multiple Web sites from four different industry sectors: airlines, online bookstores, automobile manufacturers, and car rental agencies. To enhance the external validity of the study, users were asked to assume the role of a consumer or an investor when assessing usability. Empirical results suggest that the evaluation procedure, the instrument, as well as the usability metric exhibit good properties. Implications of the findings for researchers, for Web site designers, and for heuristic evaluation methods in usability testing are offered.
Applying the Technology Acceptance Model and Flow Theory to Online Consumer Behavior
Authors: Koufaris Marios 
Published: January 2003

In this study, we consider the online consumer as both a shopper and a computer user. We test constructs from information systems (Technology Acceptance Model), marketing (Consumer Behavior), and psychology (Flow and Environmental Psychology) in an integrated theoretical framework of online consumer behavior. Specifically, we examine how emotional and cognitive responses to visiting a Web-based store for the first time can influence online consumers' intention to return and their likelihood to make unplanned purchases. The instrumentation shows reasonably good measurement properties and the constructs are validated as a nomological network. A questionnaire-based empirical study is used to test this nomological network. Results confirm the double identity of the online consumer as a shopper and a computer user because both shopping enjoyment and perceived usefulness of the site strongly predict intention to return. Our results on unplanned purchases are not conclusive. We also test some individual and Web site factors that can affect the consumer's emotional and cognitive responses. Product involvement, Web skills, challenges, and use of value-added search mechanisms all have a significant impact on the Web consumer. The study provides a more rounded, albeit partial, view of the online consumer and is a significant steptowards a better understanding of consumer behavior on the Web. The validated metrics should be of use to researchers and practitioners alike.
The Measurement of Web-Customer Satisfaction: An Expectation and Disconfirmation Approach
Authors: McKinney Vicki , Yoon Kanghyun , Zahedi Fatemeh “Mariam” 
Published: January 2003

Online shopping provides convenience to Web shoppers, yet its electronic format changes information-gathering methods traditionally used by customers. This change raises questions concerning customer satisfaction with the online purchasing process. Web shopping involves a number of phases, including the information phase, in which customers search for information regarding their intended purchases. The purpose of this paper is to develop theoretically justifiable constructs for measuring Web-customer satisfaction during the information phase. By synthesizing the expectation-disconfirmation paradigm with empirical theories in user satisfaction, we separate Web site quality into information quality (IQ) and system quality (SQ), and propose nine key constructs for Web-customer satisfaction. The measurements for these constructs are developed and tested in a two-phase study. In the first phase, the IQ and SQ dimensions are identified, and instruments for measuring them are developed and tested. In the second phase, using the salient dimensions of Web-IQ and Web-SQ as the basis for formulating first-order factors, we develop and empirically test instruments for measuring IQ and SQ-satisfaction. Moreover, this phase involves the design and test of second-order factors for measuring Web-customer expectations, disconfirmation, and perceived performance regarding IQ and SQ. The analysis of the measurement model indicates that the proposed metrics have a relatively high degree of validity and reliability. The results of the study provide reliable instruments for operationalizing the key constructs in the analysis of Web-customer satisfaction within the expectation-disconfirmation paradigm.
Antecedents of B2C Channel Satisfaction and Preference: Validating e-Commerce Metrics
Authors: Devaraj Sarv , Fan Ming , Kohli Rajiv 
Published: January 2003

Although electronic commerce (EC) has created new opportunities for businesses as well as consumers, questions about consumer attitudes toward Business-to-Consumer (B2C) e-commerce vis-à-vis the conventional shopping channels continue to persist. This paper reports results of a study that measured consumer satisfaction with the EC channel through constructs prescribed by three established frameworks, namely the Technology Acceptance Model (TAM), Transaction Cost Analysis (TCA), and Service Quality (SERVQUAL). Subjects purchased similar products through conventional as well as EC channels and reported their experiences in a survey after each transaction. Using constructs from the three frameworks, a model was constructed and tested to examine the determinants of the EC channel satisfaction and preference using the survey data. Structural equation model analyses indicate that metrics tested through each model provide a statistically significant explanation of the variation in the EC consumers' satisfaction and channel preference. The study found that TAM components—perceived ease of use and usefulness—are important in forming consumer attitudes and satisfaction with the EC channel. Ease of use also was found to be a signi.cant determinant of satisfaction in TCA. The study found empirical support for the assurance dimension of SERVQUAL as determinant in EC channel satisfaction. Further, the study also found general support for consumer satisfaction as a determinant of channel preference.
Reputation in Marketing Channels: Repeated-Transactions Bargaining with Two-Sided Uncertainty
Authors: Banks Darryl T. , Hutchinson J. Wesley , Meyer Robert J. 
Published: January 2003

Marketing channel interactions typically feature three characteristics that have not been incorporated together in an analytic study: (1) the parties can do business repeatedly over time, often under different terms of trade (e.g., prices may vary), (2) the terms that the seller offers one buyer may be different from those she offers another, giving each interaction the flavor of bilateral monopoly bargaining, and (3) the buyer and seller come to the interaction uncertain about the valuations each holds for the good, but they do know each other's reputation for valuation. The seller might, for example, come to the bargaining table aware that the buyer has a strong reputation for being willing to pay only low prices, and the buyer might come aware that the seller is strongly reputed for high cost and is, therefore, willing to offer only high prices. The latter characteristic raises an interesting question: When engaged in a marketing channel interaction, what type of reputation is best for a buyer or seller to take to the bargaining table? In this paper, we answer that question by incorporating each of the characteristics that typify channel interactions in a formal game-theoretic bargaining model. We determine how the reputations that buyers and sellers bring to the bargaining table affect their equilibrium strategies and payoffs. Our analysis shows that, in general, the best reputation for the seller to take to the bargaining table is one that makes the buyer nearly certain in his belief that the seller's cost is high, a result that matches intuition. The best reputation for the buyer, however, is counterintuitive. We show that an increase in the buyer's reputed willingness to pay can actually cause the seller to offer a lower price. The best reputation for the buyer to take to the bargaining table is, therefore, one that makes the seller believe that there is a significant chance that he is willing to pay a high price. This result is new to the literature and brings with it immediate managerial implications that we discuss. Our analysis also shows that modeling the buyer as a forward-looking strategic player yields different results than does following the normal convention of modeling the buyer as a nonstrategic price-taker. We discuss why future research on channels and on reference-dependent utility theory should consider these differences.
Order-Based Backorders and Their Implications in Multi-Item Inventory Systems
Authors: Song Jing-Sheng 
Published: January 2003

In a multi-item inventory system, such as an assemble-to-order manufacturing system or an online-retailing system, a customer order typically consists of several different items in different amounts. The average order-based backorders are the average number of customer orders that are not yet completely filled. While this is an important measure of customer satisfaction, it has not been widely studied in the operations management literature. This is largely because its evaluation involves the joint distribution of inventory levels of different items and other intricate relations, which is computationally dreadful. Taking a novel approach, this paper develops a tractable way of evaluating this measure exactly. We also develop easy-to-compute bounds, which require the evaluation of item-based backorders only. Numerical experiments indicate that the average of the lower and upper bounds is very effective. The exact results show surprisingly simple structures, which shed light on how system parameters affect the performance. Using these results, we study several examples to gain managerial insights. Questions addressed include: What are the implications of item-based inventory planning decisions on the order-based performance? What is the impact of introducing common components on inventory and service trade-offs? Would order-delivery performance be improved if we restrict the number of choices in product configurations?