SEARCH · PubMed Health

Results for “Repeatability and Reproducibility”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24Linked to original sources

PubMed2001

Chromatographic methods for product-profile analysis and isolation of oligosaccharides produced by heparinase-catalyzed depolymerization of heparin.

A two-dimensional chromatography method for monitoring the formation of oligosaccharides produced by heparinase-catalyzed depolymerization of heparin is reported. In the first step of the two-dimensional method, the depolymerized heparin is size-fractionated by high-performance gel permeation chromatography (HPGPC). The size-uniform fractions are then separated on the basis of charge by strong anion-exchange (SAX) HPLC on a high resolution CarboPac PA1 column. To demonstrate application of the two-dimensional product-profile analysis method, data are presented for the heparinase I-catalyzed depolymerization of heparin in the absence and presence of histamine, a ligand that binds site-specifically to heparin. Results from the two-dimensional analysis indicate that histamine alters the extent of depolymerization and the product-profiles for the tetrasaccharide and hexasaccharide fractions. The use of CarboPac PA1 columns for the semi-preparative scale separation of oligosaccharides in size-uniform fractions isolated from depolymerized heparin by low-pressure (gravity flow) GPC is also reported. The semi-preparative scale CarboPac PA1 column gives high resolution and excellent reproducibility after repeated use over an extended period of time, making it possible to reliably combine fractions from multiple separations. The oligosaccharides are eluted from the CarboPac PA1 column with a NaCl gradient at relatively low pH (3 or 7) where they are stable. An efficient two-step procedure is described for desalting oligosaccharides separated

Animals↗

PubMed2004

Quantification of the proliferation index of human dermal fibroblast cultures with the ArrayScan high-content screening reader.

High-throughput cell-based assays are becoming a powerful approach in the drug discovery process. The ArrayScan high-content screening (HCS) reader is a cytometer based on a fully automated fluorescence microscope that is able to obtain quantitative information on the intensity and localization of fluorescence signals within single cells over a wide cell population. The aim of this work was to set up an automated HCS multiparameter analysis for the quantification of the in vitro proliferation index of normal human dermal fibroblast (NHDF) cultures. The authors stimulated starved NHDF with insulin-like growth factor-1, platelet-derived growth factor, epidermal growth factor, fibroblast growth factor, or serum, and they quantified the proliferation index by measuring the expression of Ki-67 antigen, the incorporation of bromodeoxyuridine (BrdU), and the phosphorylation of the retinoblastoma protein (pRb). This approach also allowed quantification of the mitotic index by phospho-histone H3 staining and the percentage of cells in the S-phase by BrdU incorporation. The proliferation data from the ArrayScan assays were validated by comparison with a reference enzyme-linked immunosorbent assay (ELISA) and by flow cytometry. The measured proliferation indices were highly reproducible in repeated measures and independent experiments. The authors therefore propose that the ArrayScan HCS system could be used for high-throughput multiparameter analysis and quantification of the proliferation of cellular cultures.

Bromodeoxyuridine↗

PubMedDate not supplied

Assessment of bone mineral content and bone mass by non-invasive radiologic methods.

Methods for quantitative determination of bone mineral and bone mass in normal subjects and in patients with metabolic bone disorders can be measured by the Compton scattering technique, the neutron activation analysis, by measurement of metacarpal bone mass, by single and dual photon absorptiometry, and by quantitative computed tomography. Measurement on metacarpal bone (radiogrammetry) seems to be able to distinguish between resorption and/or new bone formation at the periosteal and/or endosteal surface. The intraindividual observer variation on combined cortical thickness (D-d), cortical area (D2-d2), metacarpal bone mass (D2-d2)/D2-varies from 0.7 to 2.5 per cent and the interindividual observer variation from 1.0 to 5.8 per cent. Single photon absorptiometry measures bone mineral content in the forearm with great precision. The reproducibility using repeated measurements and automatic selection of the measuring area is about one per cent and can be used to follow changes in mineral content with time in patients with metabolic bone diseases. The dual photon absorptiometry may be used for measurements of bone mineral content in lumbar spine, in the femoral neck and measurement of total body calcium with an accuracy of less than 6 per cent and a precision below 3 per cent. Quantitative computed tomography has the ability to measure trabecular and cortical bone both centrally and peripherally. Using CT scanning, scanner related changes with time (day-to-day variation +/- 4%), patient repositioning (less than 1.5%), and fat concentration (residual uncertainty of approximately 1/6 of the biologic variation) are important factors influencing the accuracy and reproducibility of the values of the measured bone mineral content.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Diseases, Metabolic↗

PubMedDate not supplied

[Quality specifications and allowable standards for validation of methods used in clinical biochemistry].

The purpose of this work is to provide, for a large number of analysis in the field of clinical biochemistry, appropriate criteria for the evaluation of the performance of in vitro diagnostic methods. Based on a first set of data established in 1986 and the experience cumulated by organisers in charge of internal and external quality assessment surveys, an expert group has proposed acceptable limits for a large list of analysis (n = 116). Data are reported and presented in tables divided into 7 chapters including: general biochemistry, enzymes, proteins, tumour markers, hormones, drugs (and toxic), and urinary analysis. For each analysis are given: analytical and reference ranges, three concentration levels for control specimens to be used during evaluations and the range of values within which they can be chosen, reproducibility and repeatability limits expressed as CV%. Maximal tolerable systematic error and inaccuracy are given for control and biological specimens and compared to those obtained using a reference or validated method. These data are essential for evaluations using the protocol designed by the SFBC and can serve as quality criteria for the choice and validation of in vitro diagnostic systems.

Biochemistry↗

PubMed1988

Exocrine pancreatic function test by endoscopic retrograde aspiration of pure pancreatic juice.

The validity of endoscopic retrograde aspiration of pure pancreatic juice (PPJ) as an exocrine pancreatic function test was evaluated in terms of coefficients of variation in control subjects, reproducibility on repeated examinations, and sensitivity for detecting patients with chronic pancreatitis (CP). PPJ was obtained from, nine control subjects, four patients with suspected CP and 13 with CP. PPJ was collected from within the pancreatic duct by endoscopic retrograde catheterization of the papilla at 2-min intervals for 20 minutes after a bolus intravenous injection of secretin (1U/kg) and then for further 20 minutes after a bolus intravenous injection of CCK-PZ (1U/kg). It was recognized that endoscopic aspiration of PPJ was at least as useful and reliable as the traditional pancreozymin secretin test. Useful parameters included 10-min secretory volume and 10-min bicarbonate output after secretin stimulation, and 10-min enzyme output after CCK-PZ stimulation (lipase output showed higher sensitivity than amylase output). Maximal bicarbonate concentration showed poorer reproducibility and sensitivity despite better coefficients of variation. Lower limits in controls (mean-1.5SD) were 22.5ml for 10-min secretory volume, 2.7mEq for 10-min bicarbonate output, 24.5 x 10(3)U for 10-min amylase output and 3.4 x 10(3)IU for 10-min lipase output.

Adult↗

PubMed2002

Early mitochondrial calcium defects in Huntington's disease are a direct effect of polyglutamines.

Huntington's disease (HD) is caused by an expansion of exonic CAG triplet repeats in the gene encoding huntingtin protein (Htt), but the mechanisms by which this mutant protein causes neurodegeneration remain unknown. Here we show that lymphoblast mitochondria from patients with HD have a lower membrane potential and depolarize at lower calcium loads than do mitochondria from controls. We found a similar defect in brain mitochondria from transgenic mice expressing full-length mutant huntingtin, and this defect preceded the onset of pathological or behavioral abnormalities by months. By electron microscopy, we identified N-terminal mutant huntingtin on neuronal mitochondrial membranes, and by incubating normal mitochondria with a fusion protein containing an abnormally long polyglutamine repeat, we reproduced the mitochondrial calcium defect seen in human patients and transgenic animals. Thus, mitochondrial calcium abnormalities occur early in HD pathogenesis and may be a direct effect of mutant huntingtin on the organelle.

Animals↗

PubMed2003

Performance liquid chromatographic analysis of glipizide: application to in vitro and in vivo studies.

This paper describes the validation of a sensitive, accurate, and reproducible method for the determination of a release profile of glipizide from controlled-release dosage forms. In this method, an in vitro dissolution profile of commercial controlled-release dosage forms is determined using a reversed-phase C(18) column, mobile phase (acetonitrile-buffer, 0.05 M KH(2)PO(4) adjusted to pH 3.5 with orthophosphoric acid), and UV detection at a wavelength of 275 nm. The method is validated for linearity, accuracy, precision, and detection and quantitation limits. The same method can be exploited to determine the plasma concentration of glipizide. The peak area versus plasma concentration is linear over the range of 12.5-1000 ng/mL and the detection limit was 5 ng/mL in plasma. The average accuracy was 99.90% with a relative standard deviation (RSD) of not more than 3%. Repeatability and reproducibility were found to be good with an RSD of less than 3%.

Chromatography, Liquid↗

PubMed1999

CBF and CBV measurements by USPIO bolus tracking: reproducibility and comparison with Gd-based values.

The authors measured cerebral blood flow (CBF) and cerebral blood volume (CBV) by bolus tracking of a novel ultrasmall superparamagnetic iron oxide (USPIO) contrast agent (NC100150) and compared absolute and relative perfusion measurements with those obtained by a standard gadolinium-based contrast agent. They found a linear correlation between the two methods. A dose of 0.4 mg Fe/kg body weight was found to produce a signal drop similar to that of a standard 0.2 mmol/kg gadodiamide injection using spin-echo echoplanar imaging (SE-EPI) at 1.0 T. The measurements showed a high degree of reproducibility of repeated absolute as well as relative CBF and CBV values, lending further hope to the possibility of using magnetic resonance bolus tracking for routine CBF and CBV measurements. Finally, the authors present their initial experience with high-resolution, non-EPI CBV maps obtained from steady-state levels of an intravascular superparamagnetic contrast agent.

Animals↗

PubMedDate not supplied

Liquid chromatography with mass spectrometry--detection of lipophilic shellfish toxins.

A rapid multiple toxin method based on liquid chromatography with mass spectrometry (LC/MS) was developed for the detection of okadaic acid (OA), dinophysistoxin-1 (DTX-1), DTX-2, yessotoxin (YTX), homoYTX, 45-hydroxy-YTX, 45-hydroxyhomo-YTX, pectenotoxin-1 (PTX-1), PTX-2, azaspiracid-1 (AZA-1), AZA-2, and AZA-3. Toxins were extracted from shellfish using methanol-water (80%, v/v) and were analyzed using a C8 reversed-phase column with a 5 mM ammonium acetate-acetonitrile mobile phase under gradient conditions. The method was validated for the quantitative detection of OA, YTX, PTX-2, and AZA-1 in 4 species (mussels, Mytilus edulis; cockles, Cerastoderma edule; oysters, Crassostrea gigas; king scallop, Pecten maximus) of shellfish obtained from United Kingdom (UK) waters. Matrix interferences in the determination of the toxins in these species were investigated. The validated linear range of the method was 13-250 microg/kg for OA, PTX-2, and AZA-1 and 100-400 microg/kg for YTX. Recovery and precision ranged between 72-120 and 1-22%, respectively, over a fortification range of 40-160 microg/kg for OA, PTX-2, and AZA-1 and 100-400 microg/kg for YTX. The limit of detection, reproducibility, and repeatability of analysis showed acceptable performance characteristics. A further LC/MS method using an alkaline hydrolysis step was assessed for the detection of OA, DTX-1, and DTX-2 in their esterified forms. In combination with the LC/MS multiple toxin method, this allows detection of all toxin groups described in Commission Decision 2002/225/EC.

Animals↗

PubMed1985

Airway responsiveness to inhaled antigen, histamine, and methacholine in inbred, ragweed-sensitized dogs.

We studied the responses to antigen in animals selected from a colony of inbred dogs sensitized to specific allergens to determine if they had characteristics similar to those of human asthmatics. They were immunized with ragweed and grass pollen extracts (10 micrograms in alum) immediately after routine vaccination with attenuated live virus (distemper and hepatitis) and killed bacteria (Leptospira) at 4, 8, and 12 wk of age. Subsequently, ragweed and grass injections were repeated every 2 months. Immunized dogs made specific IgE-antibodies in serum averaging 3 to 4 times that of control animals (no immunization with pollen or vaccine). They showed positive skin responses to the injection of ragweed pollen extract, whereas control dogs did not respond to ragweed pollen by quantitative skin test or inhalation challenge. In immunized dogs under barbiturate anesthesia, air-flow resistance of the total respiratory system increased from 0.60 +/- 0.07 (mean +/- SEM) before to 12.6 +/- 3.4 cm H2O/lps 5 min after the start of antigen aerosol; respiratory resistance remained increased for 20 min and was associated with 0 hypoxemia and increased arterial plasma histamine. In addition, airway responsiveness to both inhaled histamine and methacholine was greater in immunized dogs than in nonimmunized dogs of comparable age. Airway responses to each agonist were highly reproducible on repeated testing. These results indicate that physiologic responses to antigen by inbred, ragweed-sensitized dogs resemble human asthma closely and that these dogs appear suitable for a variety of experimental studies of asthma with respect to pathogenesis, diagnosis, prevention, and treatment.

Animals↗

PubMed1989

Stereological estimation of mean nuclear volume in prostatic cancer, the reproducibility and the possible value of estimations on repeated biopsies in the course of disease.

The reproducibility of stereological estimates of mean nuclear volume by using the principle of volume estimation of particles of arbitrary shape is investigated together with the possible prognostic value of the estimates in the course of advanced prostatic cancer. Repeated transurethral resection of the prostate was performed 14-93 months after the first resection in 14 of 85 consecutive patients in whom prostatic cancer was newly diagnosed in the period 1979-1983. Twelve of these fourteen patients needed endocrine treatment because of progression of the metastatic disease. The reproducibility of the estimations was excellent as the variation of the method was less than 1% when the estimation of the mean nuclear volume was repeated at random on the same specimens after a time-interval of 2 months. The progression of the disease was evidenced by a significant histological upgrading and by a highly significant increase of the mean nuclear volume from the first to the second transurethral resection of the prostate.

Aged↗

PubMedDate not supplied

Precision parameters of standard methods of analysis for dairy products.

The available collaborative studies for standard methods of analysis for various constituents of milk and milk products were examined in an attempt to assign specific repeatability and reproducibility precision parameters to these methods. The different collaborative assays for the primary constituents (moisture/solids, fat, protein), the nutritionally important elements (calcium, sodium, potassium, phosphorus), and miscellaneous analytes/physical constants (ash, lactose, salt, freezing point) produced different estimates of the precision parameters for the same method. A suitable summary of the precision estimates from collaborative studies is given by the reproducibility relative standard deviation, RSDg, which is relatively constant within a product and permits comparisons across products. An estimate of the variation of RSDR for an analyte from a number of collaborative studies is presented in terms of the median and 90% interval (the range of the centermost 90% of values). These estimates are only informative when a substantial number of independent studies are available for pooling the independent estimates to form a distribution of RSDR values. The RSDR for the determination of the primary constituents of milk and milk products is characterized by a median RSDR of 1% and a 90% interval of 0.3-3%, with RSDR estimates occasionally occurring below 0.3% and above 4%. These overall estimates appear to be independent of analyte, matrix, and method and apply to concentrations of primary constituents that range from about 2 to 80%. The repeatability relative standard deviation, RSDr, is unstable, although it tends to converge to about 0.5-0.7 X RSDR. Too few collaborative assays are available to characterize RSDR for the determination of certain other constituents (acidity, ash, lactose, salt, and the nutritionally important elements) unless RSDR values for different analytes, methods, and matrixes are pooled on the basis of similar analyte concentrations. When pooled, the RSDR values are generally better than predicted from the Horwitz equation, RSDR (%) = 2 exp (1-0.5 log10C), where C is the concentration expressed as a decimal fraction; all but one of 661 RSDR values are within the upper empirical limit of twice this curve.

Animals↗

PubMed1998

Brain MRI lesion volume measurement reproducibility is not dependent on the disease burden in patients with multiple sclerosis.

We evaluated the potential effect of the lesion burden on the reproducibility of repeated lesion volume (LV) measurements from brain magnetic resonance imaging (MRI) scans of patients with multiple sclerosis (MS). Dual-echo, conventional spin echo brain MRI scans were obtained from 107 patients with MS. On proton density-weighted images, LV was assessed three times by the same raters, using a semi-automated, local thresholding technique for lesion segmentation. Mean LV (MLV) was 16.1 mL (range = 0.7-57.3 mL). The mean intra-observer coefficient of variation (COV) for the three measurement replicates was 2.6% (range = 0.2-7.2%). The intra-observer measurement variance (Var) increased with MLV and the fitted model was Var = 0.00187 MLV1.84. This indicates that LV measurements can be considered as measures whose variances are proportional to the square of their mean values, i.e., these measures have constant COV. Using a semi-automated, local thresholding segmentation technique, the reproducibility of LV measurements from brain MRI scans of patients with MS is not significantly influenced by varying lesion burdens.

Analysis of Variance↗

PubMed1995

Antipyrine repeatability and comparison of the powder and capsule formulations.

Twelve healthy subjects (6 females), who were drug-free and non alcoholic, age 21-40 years and weight 43-80 kg took part in the study which lasted about 4 weeks. The subjects were randomly assigned into 2 panels (of 6 subjects each) and took antipyrine (1,050 mg) orally either as powder made into solution or gelatin capsules on 3 consecutive trial occasions separated by 2-week intervals. Panel A had powder, powder and capsule formulations on trials 1, 2 and 3, respectively, and panel B had capsule, capsule and powder formulations on trials 1, 2 and 3, respectively. There were no significant differences in the saliva pharmacokinetic parameters of antipyrine in the 3 trials for both panels of subjects, except the half-lives in panel B which was significantly different at the 5% level. There were no significant differences in the amounts of antipyrine and its metabolites excreted in urine in the 3 trials. The saliva concentrations of antipyrine in the 3 trials were relatively comparable. The relative bioavailability of the capsule formulation of antipyrine was 97%. This study shows that the saliva pharmacokinetic parameters of antipyrine and the amounts of antipyrine metabolites excreted in urine are highly reproducible following repeated oral administration, either in solution or as capsules. The capsule formulation is fully bioavailable and should be suitable for oral administration in assessing the influence of drugs and environmental factors on antipyrine metabolism.

Adult↗

PubMed1996

Repeated analysis of sister chromatid exchange induction by diepoxybutane in cultured human lymphocytes: effect of glutathione S-transferase T1 and M1 genotype.

Spontaneous and diepoxybutane (DEB)-induced sister-chromatid exchanges (SCEs) were examined in whole-blood lymphocyte cultures of 3 men and 4 women. A strong increase in mean number of SCEs per cell with increasing DEB concentrations (0, 2, and 4 microM) was observed in cultures of all subjects, but 3 of the donors were clearly more sensitive than the others. The SCE measurements were repeated 2-6 times per donor over a period of 55 months to assess the stability of the individual SCE response. The results showed that SCE induction by DEB was steady in the individuals during the follow-up at each DEB dose, with no significant differences among the repeated experiments. At 4 microM DEB, the DEB-sensitive and -resistant donors could be reliably be differentiated from each other in all trials. As DEB-sensitivity has been suggested to be due to the lack of glutathione S-transferase (GST) T1, the donors were genotyped for the presence of GSTT1 and GSTM1 genes. The 3 individuals found to be DEB-sensitive were all of the GSTT1 null genotype, whereas the 4 DEB-resistant donors were GSTT1 positive, which supported the role of the GSTT1 gene in determining DEB-sensitivity. Three of the DEB-resistant and none of the DEB-sensitive had the GSTM1 null genotype. Thus, the lack of the GSTM1 gene was not associated with the DEB-sensitivity trait. In conclusion, the present findings show that individual SCE responses to treatment of cultured human lymphocytes with DEB can reliably be reproduced in repeated trials. The results confirm that the GSTT1 gene but not the GSTM1 gene is important in determining individual sensitivity to the in vitro genotoxicity of DEB.

Cells, Cultured↗

PubMed2006

An alternative high-performance liquid chromatographic method for determination of clindamycin in plasma.

A simple, sensitive, selective and reproducible method based on a reversed-phase chromatography was developed for the determination of clindamycin in human plasma. Clindamycin was separated from the internal standard (phenobarbital) on a Luna C18 column (250 x 4.6 mm, 5 mm particle size: Phenomenex, USA), with retention times of 5.6 and 14.2 minutes, respectively. Ultraviolet detection was set at 210 nm. The mobile phase consisted of a solution of 0.02 M disodiumhydrogenphosphate (pH 2.8) and acetonitrile (76:24 v/v), running through the column at a flow rate of 1.0 ml/min. The chromatographic analysis was operated at 25 degrees C. Sample preparation (1 ml plasma) was done by a single step liquid-liquid extraction with water saturated ethylacetate. Calibration curves in plasma at concentrations of 0.25, 0.5, 1.0, 2.0, 4.0, 8.0 and 16.0 microg/ml were all linear with correlation coefficients better than 0.999. The precision of the method based on within-day repeatability and reproducibility (day-to-day variation) was below 15% (% coefficient of variations: %CV). Good accuracy was observed for both the intra-day and inter-day assays, as indicated by the minimal deviation of mean values found with measured samples from that of the theoretical values (below +/- 15%). Limit of quantification was accepted as 0.07 microg using 1 ml plasma sample. The mean recovery for clindamycin and the internal standard were greater than 95%. The method was free from interference from fosmidomycin, including commonly used drugs, antimalarials and antihelminthics. The method appears to be robust and has been applied to a pharmacokinetic study of clindamycin in a patient with malaria following oral doses of clindamycin at 10 mg/kg body weight given twice daily for 7 days.

Anti-Bacterial Agents↗

PubMed2002

Application of solid/liquid extraction for the gravimetric determination of lipids in royal jelly.

Gravimetric lipid determination is a major parameter for the characterization and the authentication of royal jelly quality. A solid/liquid extraction was compared to the reference method, which is based on liquid/liquid extraction. The amount of royal jelly and the time of the extraction were optimized in comparison to the reference method. Boiling/rinsing ratio and spread of royal jelly onto the extraction thimble were identified as critical parameters, resulting in good accuracy and precision for the alternative method. Comparison of reproducibility and repeatability of both methods associated with gas chromatographic analysis of the composition of the extracted lipids showed no differences between the two methods. As the intra-laboratory validation tests were comparable to the reference method, while offering rapidity and a decrease in amount of solvent used, it was concluded that the proposed method should be used with no modification of quality criteria and norms established for royal jelly characterization.

Chemistry Techniques, Analytical↗

PubMed2000

Detection of individual differences in radiation-induced apoptosis of peripheral blood lymphocytes in normal individuals, ataxia telangiectasia homozygotes and heterozygotes, and breast cancer patients after radiotherapy.

Quantification of radiation-induced apoptosis in peripheral blood lymphocytes (PBLs) has been proposed as a possible screening test for cancer-prone individuals and also for the prediction of normal tissue responses after radiotherapy. We have used the TUNEL assay (terminal transferase nick-end labeling) 24 h after irradiation with 4 Gy at high dose rate to assess interindividual differences in radiation-induced apoptosis between (1) a panel of normal individuals, (2) ataxia telangiectasia (AT) homozygotes and heterozygotes, and (3) breast cancer patients who had received radiotherapy 8-13 years ago, including a number of patients who had suffered adverse responses to radiation. With this protocol, we show clear differences in radiation-induced apoptosis between individuals, and good reproducibility in the assay. In agreement with previous reports using EBV-transformed lymphoblasts, we show a very poor induction of apoptosis in AT homozygotes and a reduced level in AT heterozygotes compared to normal individuals. A similar reduced level compared to normal individuals was seen in the breast cancer patients. Despite a wide range of values in the breast cancer patients and good reproducibility on repeat samples, there was no correlation of rates of apoptosis with the severity of breast fibrosis, retraction or telangiectasia. The reduced rate of apoptosis observed in the breast cancer cases may be associated with genetic predisposition to breast cancer; however, we conclude that assays of lymphocyte apoptosis are unlikely to be of use in predicting normal tissue tolerance to radiotherapy.

Adult↗