Results Of Interlaboratory Comparison Research Articles

Quality Control of Cell Processing and Cord Blood Storage Using HALO To Measure Proliferative Potential of Stem and Progenitor Cells.

Prior to the introduction of flow cytometry to detect and measure CD34+ cells in the early 1980s, quality control of stem cell transplants was performed using the granulocyte-macrophage colony-forming assay (GM-CFC). The major disadvantages of this growth potential assay are that progenitor and not stem cells are detected and the assay takes too long to perform. Yet, measurement of the growth potential of proliferating cell populations in vitro is the only technique that guarantees the presence of stem cells after cell processing and may predict engraftment and reconstitution. There are no assays presently that exhibit these characteristics in real-time. However, it is now possible to measure the proliferative potential of stem and progenitor cells after cell processing and/or storage in half the time required by the classical colony-forming assay (CFA). Originally developed for hemotoxicity testing for all stages of drug development, HALO (Hematopoietic/Hemotoxicity Assays via Luminescence Output) can be used as an in-line stem cell processing quality control procedure as well as a method to ensure the growth potential of processed and stored umbilical cord blood. HALO sensitively measures small numbers of proliferating cells and because cell differentiation is not detected, manual enumeration of colonies is not required. The assay is based on the CFA procedure. However, as cells proliferate in response to growth factors, there is a proportional increase in the intracellular ATP concentration. The assay is performed in a 96-well plate and release of intracellular ATP drives a luciferin/luciferase reaction to produce bioluminescence in the form of light measured in a plate luminometer. The kinetics of most hematopoietic proliferating populations, including mature stem cells, allows results to be obtained after 6–7 days in culture. Measurement of luminescence for all 96 well cultures takes about 5 minutes. An ATP standard dose response performed prior to sample measurement not only provides quality control of the reagents used, but intra- and interlaboratory comparison of results. Due to the rapid and easy set-up procedure with high-throughput capability, the proliferative capacity of several stem and progenitor cell populations from either single or large numbers of samples from bone marrow, peripheral blood or cord blood can be analyzed simultaneously. Rapid assay turnaround and multiparameter capability should therefore allow an increased safety factor for patients undergoing stem cell transplantation. Additional studies are underway to further validate this approach.

Stable oxygen isotopes from theropod dinosaur tooth enamel: interlaboratory comparison of results and analytical interference by reference standards

Although previous work has demonstrated that biological phosphates ('biophosphates') record significant changes in delta18O associated with variations in local climate and seasonality, the repeatability of these analyses between laboratories has not previously been tested. We serially sampled enamel on four Cretaceous dinosaur teeth for phosphate delta18O analysis at up to three different facilities. With the exception of one set of unprocessed enamel samples, the material supplied to each laboratory was chemically processed to silver phosphate. Each laboratory analyzed sample sets by pyrolysis (thermochemical decomposition) in a ThermoFinnigan TC/EA attached to a ThermoFinnigan Delta Plus mass spectrometer. Significant interference between phosphate samples and the NIST reference material 8557 barium sulfate (NBS 127) distorts some of the results. Samples analyzed immediately following NBS 127 may be depleted by 6 per thousand isotopically and in instrument peak amplitude response by 80%. Substantial interference can persist over the subsequent 20 silver phosphate samples, and can influence the instrument peak amplitude response from some organic standards. Experiments using reagent-grade silver phosphate link these effects to divalent cations, particularly Ca2+ and Ba2+, which linger in the reactor and scavenge oxygen evolved from pyrolysis of subsequent samples. Unprocessed enamel includes 40 wt% calcium and self-scavenges oxygen, disrupting the isotopic measurements for the first half of a set and depleting subsequent organic standards by up to 9 per thousand. In sets without NBS 127 or calcium, such interference did not occur and an interlaboratory comparison of results from enamel shows reproducible, significantly correlated peaked delta18O patterns with a 2-3 per thousand dynamic range, consistent with previous results from contemporaneous teeth. Whereas both unprocessed enamel and the NBS 127 barium sulfate should be applied to biological phosphate ('biophosphate') stable isotope research with caution, seasonal variations in enamel phosphate delta18O are a paleoecologically valuable, reproducible phenomenon in theropod dinosaur teeth.

Human urine certified reference material CZ 6009: creatinine, styrene metabolites (mandelic acid and phenylglyoxylic acid).

The reference material was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to styrene. The concentrations of mandelic acid (MA), phenylglyoxylic acid (PGA), and hippuric acid (HA) in urine were determined by three modes of high-performance liquid chromatography (HPLC). For isochronous stability testing the urinary mandelic acid and phenylglyoxylic acid concentrations were followed over a 24-month period for a preliminary batch by use of HPLC. No changes of the concentration values were found. The creatinine concentration was stable for more than five years. Standard Reference Material NIST 914a Creatinine was used for traceability purposes for creatinine. Pure chemicals MA and PGA were used for traceability purposes. Control material ClinChek-Urine Control (Recipe) was analyzed simultaneously. The mean values of MA and PGA compare well with the means and fall within the control range of control samples. Results from homogeneity, stability, and traceability testing were evaluated using the statistical program ANOVA. The certified values and their uncertainties were evaluated from the results of interlaboratory comparisons, and homogeneity and stability tests. The values are unweighed arithmetical averages of accepted results and their uncertainties are combined uncertainties (coverage factor=1).

Preliminary study to prepare a reference material of styrene metabolites - mandelic acid and phenylglyoxylic acid - in human urine

A preliminary batch of the reference material was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to styrene. Tests for homogeneity and stability were performed by determining urine concentrations of mandelic (MA) and phenylglyoxylic acids (PGA). The urinary MA and PGA concentrations were followed over an 8-month period using high performance liquid chromatography (HPLC). No changes of the concentration values were found. Pure PA and PGA from Merck and Fluka, respectively, were used for traceability purposes, because certified or standard reference materials for MA and PGA do not exist. Control material ClinChek-Urine Control (Recipe) was analysed simultaneously. The mean values of MA and PGA compared well with the means of control samples and fell within the control range. The certified values and their uncertainties were evaluated from the results of interlaboratory comparisons, homogeneity (277.0 ± 7.4 mg L−1 for MA and 148.0 ± 4.7 mg L−1 for FGA) and stability tests. The values are unweighted arithmetical averages of accepted results and their uncertainties are combined uncertainties enlarged by coefficient k=1, evaluated from the standard uncertainties of the interlaboratory comparison, homogeneity and stability tests.

Improvements in performance in medical diagnostics tests documented by interlaboratory comparison programs

There is evidence to support the notion that interlaboratory comparisons (ILCs) are an effective tool for laboratory improvement. However, despite widespread experience and anecdotal evidence of improvements there are few published studies demonstrating any benefits from ILCs– in any field of testing. Published demonstrations of benefits can help justify the growing use of ILCs. ILCs and proficiency testing have been common for many years in medical laboratories; there has been open information on the results of ILCs, and there has been standardization of results from thousands of laboratories. These studies show general improvement over time in several areas of testing in different countries. Many articles cite specific reasons for the improvements, either proven or supposed. An early version of this paper was presented at the International Laboratory Accreditation Cooperation Conference ”ILAC 2000” in Washington D.C., on 31October, 2000.

Key elements of mutual recognition arrangements

Mutual recognition arrangements in the field of metrology are concluded between equal partners to promote the acceptance of each other’s calibration certificates and test reports in order to facilitate global trade (‘‘one-step-testing’’). Acoustics is affected by this development both on the level of national metrology institutes, cooperating in organizations of the Metre Convention, and on the level of accreditation bodies and their accredited calibration and testing laboratories, cooperating in the International Laboratory Accreditation Cooperation (ILAC). Both arrangements are equivalent in the sense that they are based on mutual confidence between the partners, established mainly by the results of interlaboratory comparisons, uniform implementation of International Standards and peer assessments or accreditations.

Determination of activity of antioxidants in human subjects.

Evidence from biochemical and animal models suggests that nutritional antioxidants should inhibit the development of diseases such as CHD and certain cancers. This evidence is not clearly corroborated by intervention studies in human subjects, due, in part, to inadequacies in current analytical methodologies. Although in vitro assays can give useful information on the attributes required by a compound to act as an antioxidant, results may have little nutritional relevance due to limited bioavailability. The determination of antioxidants in blood is often used as a measure of antioxidant status in vivo, but may not necessarily reflect concentrations in target tissues where oxidative stress is greatest. In addition, the accumulation of antioxidants in selective tissues may not be apparent from plasma measurements. Participation in quality-control schemes for antioxidant determination by HPLC allows inter-laboratory comparison of results. Moderation of indices of oxidative damage to lipids, proteins and DNA can provide information on the effectiveness of compounds as nutritional antioxidants. However, most current methods of assessing oxidative stress are subject to confounding factors of non-oxidative origin. Assays for total antioxidant capacity in plasma differ in their type of oxidation source, target and measurement used to detect the oxidized product. They give different results, should never be used in isolation, and results should be interpreted with caution. Until more is known about the activity and metabolic fate of antioxidants, caution should be exercised in the consumption of large amounts of commercially-available antioxidant preparations.

Interlaboratory comparison experiment on the determination of formaldehyde emitted from mineral wool board using small test chambers

The paper presents results of interlaboratory comparison on the emission of formaldehyde from mineral wool board. Eleven laboratories took part in these studies. The results showed significant variances between laboratories. The discrepancy was related to the chamber conditions and sampling.

State-of-the-art in the measurement of volatile organic compounds emitted from building products: results of European interlaboratory comparison.

Eighteen laboratories from 10 European countries participated in a comparison organized as part of the VOCEM project, a 2.5-year research collaboration among 4 research institutes and 4 industrial companies. The scope of the project was to improve the procedure used to measure volatile organic compounds (VOC) emitted from building materials and products in small test chambers. The interlaboratory comparison included the GC-MS determination of 5 target compounds from carpet, 8 from polyvinyl chloride (PVC) cushion vinyl and 2 from paint; for the first time, chamber recovery (sinks), homogeneity of solid materials and possible contamination during transport were tested. The results show that the intralaboratory variance (random errors) is much smaller than the interlaboratory variance (systematic errors). Causes of the largest interlaboratory discrepancies were: (i) analytical errors; (ii) losses of the heaviest compounds due to sorption on the chamber walls; and (iii) non homogeneity of the materials. The output of this work concerns both the objective of labelling materials with regard to their VOC emissions and the pre-standard drafted by the European Commitee for Standardization (CEN) for this type of determination.

Low pressure chromatographic separation of inorganic arsenic species using solid phase extraction cartridges

Routine water analysis of arsenic species requires simple, inexpensive, rapid and sensitive methods. To this end, we have developed two methods, which are based on the use of inexpensive solid phase extraction (SPE) cartridges as low pressure chromatographic columns for separation and hydride generation atomic absorption spectrometry (HGAAS) and hydride generation atomic fluorescence spectrometry (HGAFS) for detection of arsenic. Both anion exchange and reverse phase cartridges were successfully used to separate arsenite [As(III)] and arsenate [As(V)]. The composition, concentration, and pH of eluting buffers and the effect of flow rate were systematically investigated. Speciation of inorganic As(III) and As(V) were achieved within 1.5 min, with detection limits of 0.2 and 0.4 ng/ml, respectively. Both isocratic and step gradient elution techniques were suitable for the baseline resolution of As(III) and As(V) using anion exchange cartridges. Application of the methods to the speciation of As(III) and As(V) in untreated water, tap water, and bottled water samples were demonstrated. Results from the speciation of arsenic in a standard reference material water sample using these methods were in good agreement with the certified value and with inter-laboratory comparison results obtained using HPLC separation and inductively coupled plasma mass spectrometric detection (HPLC–ICPMS).

Monitoring by Excretion Analysis: Results of Interlaboratory Comparisons

The measurement of radioactivity concentrations in urine samples is an important tool for the monitoring of possible radionuclide intakes by occupationally exposed workers, especially for those radionuclides emitting alpha or beta radiation. The new German guideline for requirements for measuring laboratories requires measures for standardisation and quality assurance by all laboratories responsible for such measurements. For this purpose the working group 'Incorporation Monitoring (AKI)' of the German-Swiss Radiation Protection Association has already performed, in the period from 1981 to 1997, interlaboratory comparisons of uranium, thorium, americium, lead, strontium and tritium in urine. The results and their implications for internal dosimetry are presented.

The influence of different evaluation techniques on the results of interlaboratory comparisons

The influence of different evaluation techniques on the results of an interlaboratory comparison for the determination of nutrients in ground- and surface water was investigated. The outlier-test procedure was found to influence the interlaboratory standard deviations (SDs), but not the averages. It was shown that even small differences in the numbers of outliers detected can change the SD severely. Comparing the outlier-test procedures of Hampel, Grubbs and Graf-Henning, it was found that Hampel's test detected the most outliers, thus generally resulting in smaller SDs between interlaboratory comparisons. The Graf-Henning test detected the fewest outliers and its application resulted in the highest SDs of the three test procedures investigated. The comparison of different summarising indices, namely the rescaled sum of z-scores, average of absolute z-scores and average deviation showed no comparability. Possibilities to improve the comparability of interlaboratory comparisons and to minimise misunderstandings are suggested.

International Standards for growth factors and cytokines

Growth factors and cytokines are polypeptides with a wide range of potential therapeutic and diagnostic applications. They are complex biological molecules which cannot be completely characterized by physicochemical analysis alone, and require some form of bioassay to determine their potency. Bioassay systems are themselves inherently variable, so comparison of the potency of a growth factor or cytokine preparation with that of a common reference standard is necessary to permit interassay and interlaboratory comparison of results. The National Institute for Biological Standards and Control (NIBSC) is engaged in a program to develop World Health Organization (WHO) International Standards (IS) for growth factors and cytokines. These are preparations ampouled following WHO guidelines, characterized in an international collaborative study for their potency, stability and suitability to serve as standards, assigned a unitage in International Units (IU), and established by WHO as the IS for that growth factor or cytokine. IS are are available, on request, for use, usually through calibration of local standards, in defining the potency in IU of therapeutic products, in calibration of diagnostic immunoassays and calibration of biological assays and immunoassays in biological and medical research.

Results of inter-laboratory comparisons of two methods of determining the heat of combustion of natural gas

The D. I. Mendeleev All-Union Scientific Research Institute of Metrology has performed an inter-laboratory comparison of two methods of determining the heat of combustion of natural gas: the direct calorimetric method; and an indirect computational method involving the use of gas chromatography to determine the composition of the gas. The comparison was done with the same level of accuracy maintained in the determination of standards. Good agreement was obtained between the results of the two methods for two samples of natural gas from pipelines. The gas was dried before measurement in each case. The difference seen in the two sets of results might be related to the concentration of water vapor in the gas, which was not checked in the investigation.

Relevance of nucleic acid amplification techniques for diagnosis of respiratory tract infections in the clinical laboratory.

Clinical laboratories are increasingly receiving requests to perform nucleic acid amplification tests for the detection of a wide variety of infectious agents. In this paper, the efficiency of nucleic acid amplification techniques for the diagnosis of respiratory tract infections is reviewed. In general, these techniques should be applied only for the detection of microorganisms for which available diagnostic techniques are markedly insensitive or nonexistent or when turnaround times for existing tests (e.g., viral culture) are much longer than those expected with amplification. This is the case for rhinoviruses, coronaviruses, and hantaviruses causing a pulmonary syndrome, Bordetella pertussis, Chlamydia pneumoniae, Mycoplasma pneumoniae, and Coxiella burnetii. For Legionella spp. and fungi, contamination originating from the environment is a limiting factor in interpretation of results, as is the difficulty in differentiating colonization and infection. Detection of these agents in urine or blood by amplification techniques remains to be evaluated. In the clinical setting, there is no need for molecular diagnostic tests for the diagnosis of Pneumocystis carinii. At present, amplification methods for Mycobacterium tuberculosis cannot replace the classical diagnostic techniques, due to their lack of sensitivity and the absence of specific internal controls for the detection of inhibitors of the reaction. Also, the results of interlaboratory comparisons are unsatisfactory. Furthermore, isolates are needed for susceptibility studies. Additional work remains to be done on sample preparation methods, comparison between different amplification methods, and analysis of results. The techniques can be useful for the rapid identification of M. tuberculosis in particular circumstances, as well as the rapid detection of most rifampin-resistant isolates. The introduction of diagnostic amplification techniques into a clinical laboratory implies a level of proficiency for excluding false-positive and false-negative results.

Relevance of nucleic acid amplification techniques for diagnosis of respiratory tract infections in the clinical laboratory.

Clinical laboratories are increasingly receiving requests to perform nucleic acid amplification tests for the detection of a wide variety of infectious agents. In this paper, the efficiency of nucleic acid amplification techniques for the diagnosis of respiratory tract infections is reviewed. In general, these techniques should be applied only for the detection of microorganisms for which available diagnostic techniques are markedly insensitive or nonexistent or when turnaround times for existing tests (e.g., viral culture) are much longer than those expected with amplification. This is the case for rhinoviruses, coronaviruses, and hantaviruses causing a pulmonary syndrome, Bordetella pertussis, Chlamydia pneumoniae, Mycoplasma pneumoniae, and Coxiella burnetii. For Legionella spp. and fungi, contamination originating from the environment is a limiting factor in interpretation of results, as is the difficulty in differentiating colonization and infection. Detection of these agents in urine or blood by amplification techniques remains to be evaluated. In the clinical setting, there is no need for molecular diagnostic tests for the diagnosis of Pneumocystis carinii. At present, amplification methods for Mycobacterium tuberculosis cannot replace the classical diagnostic techniques, due to their lack of sensitivity and the absence of specific internal controls for the detection of inhibitors of the reaction. Also, the results of interlaboratory comparisons are unsatisfactory. Furthermore, isolates are needed for susceptibility studies. Additional work remains to be done on sample preparation methods, comparison between different amplification methods, and analysis of results. The techniques can be useful for the rapid identification of M. tuberculosis in particular circumstances, as well as the rapid detection of most rifampin-resistant isolates. The introduction of diagnostic amplification techniques into a clinical laboratory implies a level of proficiency for excluding false-positive and false-negative results.

Quality control by the Society of Hair Testing

In contrast to urine and blood analyses the amount of hair samples lies in the order of 20–100 mg. Consequently at similar concentrations the absolute detection limit is about one order lower, increasing the relative deviation. The interlaboratory differences are correspondingly high. Concerning blood and urine, calibrators and controls are produced by adding certain amounts of the drug to the negative sample. Usually the single determinations are calibrated with spiked hair samples. These samples cannot be used as controls because in real hair the drug is bound to a solid phase surrounded by keratin, whereas in a spiked sample the drug is bound to the surface of the hair and can easily be washed away by any liquid phase. Recently some round robin surveys have been performed by several laboratories, some using drug soaked hair to detect contamination, the other using powdered hair of drug addicts to compare quantitative results. In this contribution the manufacturing of the hair pools and the results of the last international interlaboratory comparison will be described and future activities of the Society of Hair Testing are presented.

Estimation of variance components from the results of interlaboratory comparisons

Interlaboratory comparisons are frequently carried out in analytical laboratories either as a part of their quality assurance procedures or as an important part of analytical method development. The total analytical error is usually composed of three components: the random measurement error, laboratory bias and sample—laboratory interaction. The significance of these error components and the estimates of their variances can in principle be obtained from a properly designed experiment by carrying out the analysis of variance. If the samples used in the interlaboratory comparison cover a wide concentration range it is usual that the errors are not independent of concentration and, consequently, the estimation of all three error components is difficult. In this paper a scaling procedure for the initial data is proposed that makes it possible to estimate all three error components.

Estimation of variance components from the results of interlaboratory comparisons

Interlaboratory comparisons are frequently carried out in analytical laboratories either as a part of their quality assurance procedures or as an important part of analytical method development. The total analytical error is usually composed of three components: the random measurement error, laboratory bias and sample—laboratory interaction. The significance of these error components and the estimates of their variances can in principle be obtained from a properly designed experiment by carrying out the analysis of variance. If the samples used in the interlaboratory comparison cover a wide concentration range it is usual that the errors are not independent of concentration and, consequently, the estimation of all three error components is difficult. In this paper a scaling procedure for the initial data is proposed that makes it possible to estimate all three error components.

Autoantibodies against topoisomerase I detected with the natural enzyme and overlapping recombinant peptides

Antibodies against topoisomerase I (anti-topo I, anti-Scl-70) are regarded as a marker of systemic sclerosis. The various frequencies of anti-topo I detected in those patients depends at least in part on the test design and the kind of the antigen used. We therefore analyzed three overlapping recombinant topo I fragments (N-terminal, center and C-terminal part of the molecule) covering the full length of the enzyme for substitution of highly purified natural antigens (n-topo I) in ELISA for antibody screening. 49 of 50 sera reacting with n-topo I in ELISA also recognized the recombinant C-terminal topo I fragment under identical test conditions, 37 sera recognized the recombinant center and two sera the recombinant N-terminal peptide. All sera reactive with the N-terminal and center peptide reacted with the recombinant C-terminus which therefore may substitute for the natural antigen. In immunoblot assays 92% ( 46 50 ) of the sera reacted with n-topo I and 86% ( 43 50 ) with the recombinant C-terminal peptide. Immunoblots therefore seem to be less sensitive for detecting anti-popo I antibodies than ELISA regardless the source of the antigen used. In a screening of 696 sera submitted for routine antibody tests the recombinant peptide ELISA on the other hand detected two sera which did not react with n-topo I in ELISA. Because of the high rate of agreement within the results obtained with the two antigens, n-topo I can be substituted by the recombinant peptide ELISA allowing better standardization and interlaboratory comparison of results.