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A B Heath

Publications and source records attributed to A B Heath.

At least 19 recordsLinked to original sources
PubMed2006

An International Standard for specifying the minimum potency of anti-D blood-grouping reagents: evaluation of a candidate preparation in an international collaborative study.

BACKGROUND AND OBJECTIVES: The aim of this study was to evaluate a lyophilized monoclonal immunoglobulin M (IgM) anti-D preparation for use as an International Standard to specify a recommended minimum acceptable potency of anti-D blood-grouping reagents. MATERIALS AND METHODS: The candidate International Standard (99/836) for specifying the minimum potency of anti-D blood-grouping reagents was evaluated against a wide range of commercial anti-D blood-grouping reagents in an international collaborative study involving 20 laboratories in 13 countries. Laboratories titrated reconstituted 99/836, in parallel with as many commercial anti-D blood-grouping reagents as were available to them, in tube tests according to specified haemagglutination methodology for low-protein (e.g. monoclonal IgM) and high-protein (e.g. polyclonal) reagents. The ratios of the mean end-point titres of the reagents to that of 99/836 within each laboratory were calculated. RESULTS: The ratios of the mean titres of the low-protein reagents to the mean titre of 99/836 within a laboratory fell between 0.25 and 2 for 43 of the 45 low-protein anti-D reagents tested (i.e. the potencies of the low-protein reagents compared with 99/836 were between a 1:4 dilution of 99/836 to twice as potent as 99/836). The ratios of the mean titres of the high-protein reagents to the mean titre of 99/836 within a laboratory fell within 0.125 and 1 for eight out of the 10 high protein reagents tested. CONCLUSIONS: By international consensus, a 1:3 dilution of reconstituted 99/836 was deemed appropriate to define a recommended minimum acceptable potency of low-protein anti-D blood-grouping reagents. A 1:8 dilution of reconstituted 99/836 was deemed appropriate to define a recommended minimum acceptable potency of high-protein anti-D blood-grouping reagents. On the basis of the results presented here, 99/836 was established by the World Health Organization as the 1st International Standard for specifying the minimum potency of anti-D blood-grouping reagents, in tube tests.

Antibodies, Monoclonal↗
PubMed2006

International standards for minimum potency of anti-A and anti-B blood grouping reagents: evaluation of candidate preparations in an international collaborative study.

BACKGROUND AND OBJECTIVES: The aim of the study was to evaluate lyophilized monoclonal IgM anti-A and anti-B preparations for use as international standards (IS) to specify recommended minimum potencies of anti-A and anti-B blood grouping reagents in tube tests. MATERIALS AND METHODS: The candidate IS for minimum potency of anti-A and anti-B blood grouping reagents, codes 03/188 and 03/164, respectively, were evaluated against a wide range of commercial anti-A and anti-B blood grouping reagents in an international collaborative study involving 16 laboratories in nine countries. Laboratories titrated 03/188 and 03/164 in parallel with as many commercial anti-A and anti-B blood grouping reagents, respectively, as were available to them, in tube tests according to specified haemagglutination methodology. Three of these laboratories and a further laboratory also titrated 03/188 and 03/164 in parallel with currently available reference preparations for anti-A and anti-B. The ratios of the mean endpoint titres of the anti-A and anti-B reagents to those of 03/188 and 03/164, respectively, within each laboratory were calculated. RESULTS: The ratios of the mean titres of the anti-A reagents to the mean titre of 03/188 within a laboratory fell within 0.062 and 4, i.e. the potencies of the anti-A reagents were between a sixteenth to four times as strong as 03/188. The ratios of the mean titres of the anti-B reagents to the mean titre of 03/164 within a laboratory also fell within 0.062 and 4, with one outlier. CONCLUSIONS: By international consensus, a 1 in 8 dilution of the candidate IS for anti-A, 03/188, and a 1 in 4 dilution of the candidate IS for anti-B, 03/164, were considered appropriate to define the recommended minimum potencies of anti-A and anti-B blood grouping reagents, respectively, in tube tests. On the basis of these results, preparations 03/188 and 03/164 were established by the World Health Organization as International Standards for Minimum Potency of Anti-A and Anti-B Blood Grouping Reagents respectively, and by the US Food and Drug Administration Center for Biologics Evaluation and Research as Minimum Potency Reference Reagents.

ABO Blood-Group System↗
PubMed2004

Standardization of factor VIII and von Willebrand factor in plasma: calibration of the WHO 5th International Standard (02/150).

Calibration of the 5th International Standard factor (F)VIII/von Willebrand factor in plasma (02/150) (5th IS) for five parameters [factor VIII: coagulant activity (FVIII:C); FVIII: antigen (FVIII:Ag), von Willebrand factor: antigen (VWF:Ag), von Willebrand factor: ristocetin cofactor (VWF:RCo), von Willebrand factor: collagen binding (VWF:CB)] was achieved through an international collaborative study involving 37 laboratories. Estimates calculated relative to the previous 4th IS and locally prepared normal plasma pools were not significantly different for estimates of FVIII:Ag, VWF:Ag, VWF:RCo and VWF:CB and hence mean values calculated relative to the 4th IS of 0.94, 0.91, 0.78 and 0.94 IU ampoule(-1), respectively, were assigned. However, estimates for FVIII:C relative to the fresh normal pools (mean 0.61 IU ampoule(-1)) were significantly lower than estimates relative to the 4th IS (mean 0.68 IU ampoule(-1)). In consideration of the good stability of FVIII:C in the 4th IS and the variability of estimates relative to the local pools it was agreed to assign the mean value obtained relative to the 4th IS of 0.68 IU ampoule(-1). For all five parameters the interlaboratory variability (geometric coefficient of variation, GCV%) was larger for estimates calculated relative to the normal pools (range 12.6-16.5%) when compared with estimates calculated relative to the 4th IS (range 3.5-8.3%). An accelerated degradation study performed in six laboratories indicated that the five calibrated parameters are extremely stable when ampoules are stored at -20 degrees C. Mean estimates of predicted loss per year at -20 degrees C ranged from 0% for VWF:CB to 0.029% for VWF:RCo. The 5th IS (02/150) was established by the World Health Organization in November 2003.

Blood Coagulation↗
PubMed2003

Variability in factor VIII concentrate measurement: results from SSC field collaborative studies.

Seven 'field' collaborative studies on factor (F)VIII concentrate potency measurements were carried out, using local routine methodology, standards and calculation of results. Data from five of the 12 different concentrates studied are described in detail. These studies revealed that, for the intermediate-purity and the recombinant FVIII concentrates, one-stage potencies were significantly lower than chromogenic potencies, whilst for the two high-purity FVIII concentrates one-stage potencies were significantly greater than chromogenic potencies. On comparing predilution methods for the intermediate-purity concentrate, equivalent potencies were obtained using either buffer or FVIII-deficient plasma as prediluent. For the two high-purity and the recombinant concentrates, potencies obtained using buffer as prediluent were significantly greater and lower, respectively, than potencies obtained using FVIII-deficient plasma as prediluent. Interlaboratory variabilities were compared over all 12 concentrates studied and coefficients of variation (CVs) for one-stage assays were found to be much greater than for chromogenic assays. This was true for all concentrates except for the intermediate-purity concentrate and samples A and B from the first study, where the reverse was true. Furthermore, much better CVs were obtained when using FVIII-deficient plasma than when using buffer as prediluent, for all FVIII concentrates except for the intermediate-purity concentrate where the reverse was true, and sample B where CVs were equivalent. Overall, CVs were far worse than those obtained in controlled collaborative studies. Generally, however, CVs were better with chromogenic assays and predilution in FVIII-deficient plasma, as is recommended by the International Society on Thrombosis and Haemostasis/Scientific and Standardization Committee, particularly for higher purity and recombinant concentrates.

Chromogenic Compounds↗
PubMed2002

Analysis of an in vivo assay for inactivated polio vaccine.

Approaches to the statistical analysis of data from the rat bioassay for Inactivated Polio Vaccine are discussed and compared, using data from a recent collaborative study The measured response, an antibody titre obtained from a doubling dilution series, did not satisfy the requirements of normality and homogeneity of variance necessary for the standard parallel line model for quantitative data. Laboratory-specific cut-offs can be defined, to reduce the data to "positive" or "negative" responses, allowing valid analysis with the probit method.

Animals↗
PubMed2001

A collaborative study to establish the 6th International Standard for factor VIII concentrate.

A study was carried out to replace the 5th WHO International Standard (IS) for factor VIII concentrate, because of depletion of stocks. Two candidate concentrates (X and Y) were assayed as potential replacements against the 5th IS for FVIII concentrate, in a collaborative study involving 33 laboratories. Collaborators were asked to use the ISTH/SSC recommendations, including pre-dilution of concentrates in FVIII deficient plasma in their assays. Several laboratories performed more than one assay method and altogether there were 21 sets of assays with the one-stage method, 6 with the two-stage method and 26 with the chromogenic method. There was good agreement between laboratories using each method for the comparison of concentrates X and Y against the 5th IS, but the overall potencies by one-stage and chromogenic methods each differed by approximately 5% from the overall mean, with the chromogenic potency approximately 10% higher than the one-stage. Inter-laboratory agreement was slightly better for concentrate Y than X, and stability studies indicated that Y was more stable than X. After considering all the information, together with comments from participants and from the FVIII/FIX Subcommittee of the ISTH/SSC, candidate Y (NIBSC code [97/616]), was proposed and accepted in October, 1998, by the Expert Committee on Biological Standardisation of the World Health Organisation to be the 6th International Standard for Factor VIII Concentrate with an assigned potency of 8.5 IU/ampoule.

Analysis of Variance↗
PubMed1999

An international collaborative study on the detection of an HIV-1 genotype B field isolate by nucleic acid amplification techniques.

An international collaborative study to assess inter-laboratory variation in the sensitivity of gene amplification assays for the detection of HIV-1 RNA sequences was conducted using a panel of eight duplicate dilutions of an HIV-1 genotype B clinical isolate and negative control samples. Twenty-five laboratories participated in the study and used a variety of in-house assays and commercial assay systems. With few exceptions, the assays were more sensitive than a p24 antigen assay. Overall, the PCR-based Amplicor Monitor assay was the most sensitive and gave the highest mean copy number for any one sample. Some of the in-house assays gave results comparable with the Monitor assay whilst the NASBA and bDNA assays appeared to be less sensitive. As a result of this study, an HIV-1 Working Reagent for the standardisation of nucleic acid amplification assays was developed and assessed in a subsequent study. Similar differences in sensitivity between the different assay systems was observed. The discrepancies in viral copy number obtained using the Working Reagent highlights the need for an International Standard against which all Working Reagents may be calibrated.

Adult↗
PubMed1999

Assay of humoral immunity to mumps virus.

One hundred randomly chosen sera from blood donors from North London were assayed for antibodies to mumps virus by plaque reduction and microtitre neutralisation assay, haemagglutination inhibition and in-house ELISA. The assay reproducibility was determined, and there was reasonable agreement between antibody levels measured by the two neutralising methods. Neutralising antibody levels measured by either method were low but the strain used in the assay had a large effect on the antibody titres observed. Titres measured by neutralisation assay, HI assay and ELISA did not correlate well. Assessment of immunity to mumps virus remains problematical.

Adolescent↗
PubMed1999

A collaborative study to establish the 2nd International Standard for Antithrombin Concentrate.

Eighteen laboratories participated in a collaborative study to calibrate a replacement for the 1st International Standard for Antithrombin. Concentrate (88/548). Excellent agreement between laboratories, as indicated by mean % gcv of 3.3 and 5.9 for functional and antigenic assays, was observed when the candidate concentrate (96/520) was assayed against the 1st International Standard for Antithrombin, Concentrate (88/548). The functional potency was found to be 7.9% (p<0.05) lower than the antigenic potency. Based on the results and with the agreement of the participants of this study and the authorisation of the Expert Committee on Biological Standardisation of the World Health Organisation, the antithrombin concentrate, coded 96/520, has been established as the 2nd International Standard for Antithrombin, Concentrate, with labelled potencies for both functional (4.7 IU/ampoule) and antigenic (5.1 IU/ampoule) activities.

Antithrombins↗
PubMed1999

Validation of in vitro assays for botulinum toxin: a case study.

Ensuring the reliability and precision of assay results requires careful attention to assay design. In this case study we describe validation studies of an in vitro assay for botulinum neurotoxin type A based on its endopeptidase activity towards immobilised synthetic substrate. This assay, in common with many in vitro assays, is sensitive to changes in reagents and assay conditions and is time dependent. In addition, the toxin is not stable in solution. Differences in estimates of potency, resulting from positional factors, which are not significant in individual assays, are shown to be consistent and statistically significant over a longer series of assays. This study emphasizes that assay validation should not be viewed as a single step in assay development but must be considered as a continuing process if assay results are to be reliable and reproducible.

Analysis of Variance↗
PubMed1997

A new WHO International Reference Reagent for use in potency assays of inactivated poliomyelitis vaccine.

Assays of the potency of inactivated poliovirus vaccine require the use of an appropriate reference reagent. Preparation 91/574 was shown by international collaborative study to be suitable for determination of antigenic content and immunogenicity of inactivated poliovirus vaccines by in vitro and in vivo assays, respectively. The reagent is a trivalent blend of formaldehyde-inactivated monovalent pools of poliovirus type 1 (Mahoney) poliovirus type 2 (MEF-1) and poliovirus type 3 (Saukett). Studies by antigen-capture ELISA showed that the component monovalent pools contained high titres of D antigen and trace amounts of C antigen. Sucrose gradient analysis showed that the D antigenicity was almost exclusively associated with 150S virus particles. Low levels of procapsids (75S particles with D antigenicity) were detected in the type 1 and 2 monovalent pools. The profile of intact virions and procapsids in 91/574 in sucrose gradients was very similar to PU78-02, a previously used inactivated trivalent poliovirus vaccine reference. The World Health Organization (WHO) Expert Committee on Biological Standardization at its 1994 meeting established preparation 91/574 as the 2nd WHO international Reference Reagent for poliomyelitis vaccine (inactivated). A potency of 430, 95, 285 D antigen units per ml was assigned to poliovirus type 1, 2 and 3, respectively. A separate aliquot of this preparation, established by the European Pharmacopeia Commission as a Biological Reference Preparation, has an identical assigned titre. The 2nd WHO International Reference Reagent 91/574 is intended for calibration of secondary reference reagents.

Animals↗
PubMed1997

Clustering of mumps virus isolates by SH gene sequence only partially reflects geographical origin.

The nucleotide sequences of the SH gene of 45 new mumps virus isolates derived from different parts of Europe, Canada and USA were determined. A phylogenetic tree was constructed which confirmed the existence of three major clusters. While clustering according to geographical origin was clear in some cases each of the major clusters included isolates which were widely separated in origin. The degree of variability between the sequences of SH genes of different strains and the ratio of coding to non coding differences were both very high compared to those observed in other genes such as the M and HN. A standardized system of nomenclature of mumps strains was established.

Amino Acid Sequence↗
PubMed1995

A collaborative study on DNA quantitation in biological products.

In 1988, a collaborative study was set up to examine the sensitivity and reproducibility of assays for the detection of DNA in biologicals derived from continuous cell lines. Fifteen laboratories analyzed 12 samples containing different amounts of DNA and protein. When no or very little DNA was present in the test samples, false positives or overestimation was common. In contrast, when higher levels of DNA were present underestimation was the norm. The study also revealed a high degree of variability between laboratories.

Biological Products↗
PubMed1995

A WHO collaborative study of immunogenicity assays of inactivated poliovirus vaccines.

Ten laboratories studied the immunogenicity of six trivalent inactivated poliovirus vaccines in a WHO Collaborative Study. The antigenic content of all six vaccines had previously been estimated in an earlier study (Wood et al., 1995). In collaboration with the European Pharmacopoeia Commission an additional preparation, European Pharmacopoeia Biological Reference Preparation Batch 1, was also included. Laboratories were requested to use established immunogenicity assays and six used the European Pharmocoepia guinea pig/chick test while three used a rat potency test. One laboratory contributed data from both methods. Apart from one laboratory, within laboratory variation was low (less than five-fold). However, very large (greater than 100-fold) variation was seen between laboratories for ED50 results in the guinea pig/chick test. Different decisions on pass/fail outcome would have occurred for some of the samples tested. Between laboratory variation was much lower (less than five-fold) in the rat test. Expression of results as potencies relative to a standard reduced between laboratory variation for both methods, substantially so for the guinea pig/chick test. The correlation between in vivo and in vitro results was generally good with the exception of the type 3 component of one preparation. This showed that the relationship between immunogenicity and antigenicity was not necessarily predictable. There is an urgent need to revise the European Pharmocoepia immunogenicity test but it is premature, on the basis of this study, to recommend either the rat test or in vitro tests as replacements. Two candidate reference materials were both found suitable for in vivo assay of inactivated poliovirus vaccine.

Animals↗
PubMed1995

A WHO Collaborative study on assays of the antigenic content of inactivated poliovirus vaccines.

In the first phase of a two part WHO Collaborative study, fourteen laboratories from ten countries estimated the antigenic content of six trivalent inactivated poliovirus vaccine preparations using in vitro methods. All laboratories used a candidate standard method for D antigen assay (method A) and eight contributed results from established 'in-house' methods (method B). All methods assayed D antigen in an antigen capture ELISA format. Monoclonal antibodies were used as detector reagents in method A and in some laboratories for method B. The average difference in potency estimates for duplicate preparations A and C was used to assess within assay variation. Overall this was found to be 22% and 19% for methods A and B respectively. Within laboratory variation was measured as the geometric coefficient of variation for between assay repeatability. Results for methods A and B, 28% and 26% respectively were again very similar. Variation in potency estimates between laboratories was in the range 2- to 5-fold for most samples and most laboratories irrespective of the method used. However, a maximum 24-fold difference occurred when all results were taken into account. Method A gave significantly enhanced potency estimates for the type 3 component of preparation B, a vaccine shown to be immunogenic in humans in clinical trials, compared to method B. Method A also failed to assay the type 3 component of preparation F which was prepared by inactivation of the Sabin 3 strain of poliovirus. Further work is required to identify monoclonal antibodies, or combinations of monoclonal antibodies, suitable for universal application in D antigen assays of inactivated poliovirus vaccines. Further work is also required to improve control of the antigen-capture ELISA in some laboratories. The second phase of this WHO Collaborative Study evaluated the proficiency of in vivo potency assays. These results together with an evaluation of the correlation of immunogenicity and antigenic assay plus assessment of candidate reference materials will be reported separately.

Antigens, Viral↗
PubMed1995

Development and evaluation of a competitive radioimmunoassay using monoclonal antibodies against Rh D for determining anti-D potency of clinical grade immunoglobulin preparations.

A competitive radioimmunoassay using monoclonal anti-D antibodies has been developed for measuring anti-D activity in prophylactic immunoglobulin preparations. The assay is totally specific for anti-D, reproducible and gives potency estimates comparable to those determined using autoanalyzer methodology. The assay also provides a means for comparing different batches of monoclonal anti-D preparations for red-cell binding activity.

Antibodies, Monoclonal↗
PubMed1995

A collaborative study of proposed European Pharmacopoeia reference preparations of low molecular mass heparin.

A European collaborative study, in which 16 laboratories participated, was carried out to assess the performance of the European Pharmacopoeia (EP) monograph methods for anticoagulant activities (anti-Xa and anti-IIa assays) of low molecular mass (LMM) heparin and to assess the suitability of six candidate materials as the EP working standard for LMM heparin. There was good interlaboratory agreement for both types of assays as indicated by most gcy's being less than 10%, indicating acceptable performance of the EP assay methods. All the candidate preparations gave dose-response curves parallel to the 1st International Standard for Low Molecular Weight heparin and to each other. All preparations, possibly with the exception of E and F, gave similar performance as measured by interlaboratory agreement and would be suitable as working standards. Based on these data, preparations A, B, C and D have been established by the EP as official EP Biological Reference Preparations and they will be issued as successive batches.

Anticoagulants↗