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Biomedical subjects

J A Barbara

Publications and source records attributed to J A Barbara.

At least 91 records · Page 5Linked to original sources
PubMed1991

Non-A, non-B hepatitis and the anti-HCV assay.

The successful cloning of a non-structural antigen from the genome of what is now designated as the 'hepatitis C virus' (HCV) has transformed an erstwhile diagnosis of exclusion for non-A, non-B hepatitis (NANBH). The assay has been validated against panels of known infectivity for NANBH and sera from haemophiliac patients treated either with virally inactivated or uninactivated factor VIII. The predictive value of the assay is being assessed clinically in prospective studies of post-transfusion hepatitis and by using laboratory techniques such as polymerase chain reaction. While the assay shows good predictability in high-risk subjects, an appreciable number of false-positive results are likely in blood donor populations. Furthermore, the extent of infectivity of seropositive blood donors is still the subject of active research. The prevalence of anti-HCV in blood donors varies from approximately 0.2 to 1.5% around the world, based on repeat reactivity in the Ortho antiglobulin ELISA assay. These rates may be appreciably reduced following supplementary testing with recombinant immunoblot assay (RIBA). Prevalence data in African sera are as yet unreliable, pending assessment by RIBA, presumably because of high levels of IgG interfering with the assay. Presence of anti-HBc or elevated alanine aminotransferase associates to a greater or lesser extent with seropositivity, especially when both surrogate markers are present, but conversely many (unconfirmed) seropositive subjects lack these surrogate markers. An understanding of the modes of transmission of HVC is of obvious importance to transfusion practice. Intravenous drug use is a striking risk factor, but the contribution made by sexual transmission is not so clear.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Hepatitis C virus screening: UK Blood Transfusion Service on the threshold.

The implications of testing all blood donations in the UK for antibody to hepatitis C virus (HCV) are considered. Although the risks of serious liver disease arising from transfusion-transmitted HCV are relatively low in the UK, the cost of such screening will be high in terms of financial outlay and lost donations. In the UK, at least, screening of all blood donations for anti-HCV is unlikely to be as cost effective as screening for HBsAg or anti-HIV.

Antigens, Viral↗
PubMed1991

Anti-HIV-1: extended validation of a modified gelatin particle agglutination assay, and its use with an image analyser.

Modification of a commercial gelatin particle agglutination assay for anti-HIV-1 (MAT) has increased sensitivity, reduced reaction time and lowered the cost by 90%. We tested over 10,000 blood donations in parallel with the ELISA currently in use, and found the modified test to be highly sensitive and to enhance cost-effectiveness as it substantially reduces false-positive rates. The patterns of agglutination are clearly reproducible and readable by the naked eye and/or Image Analyzer, which provides objectivity and hard-copy documentation of results.

Agglutination Tests↗
PubMed1990

Detection of hepatitis C viral sequences in blood donations by "nested" polymerase chain reaction and prediction of infectivity.

Of 1100 blood donations tested during a prospective study of post-transfusion non-A, non-B hepatitis (NANBH), 6 (0.55%) were repeatedly reactive in a commercial assay for antibodies to the C100 protein of hepatitis C virus. Only 1 of the 6 donations (17%) transmitted NANBH to a recipient. Hepatitis C virus RNA sequences were detected in the serum of the transmitting donor by an assay which used the polymerase chain reaction (PCR) and non-radioisotopic detection. No such sequences were detected in the other 5 donors positive for anti-C100. Stored serum samples from blood donors who had been involved in three episodes of post-transfusion NANBH in 1981 also contained hepatitis C viral sequences. Although the PCR assay in its present form is not suitable for mass donor screening, the presence of hepatitis C viral sequences detected by PCR in blood donations seems a better predictor of infectivity than the presence of anti-C100 alone.

Antigens, Viral↗
PubMed1990

Blood donor screening for parvovirus B19.

A programme of blood donor screening for parvovirus B19 was conducted from January to May 1990. The main aim of the study was to identify a B19 positive donation that could be used as a source of viral antigen for diagnostic serology. Out of 24,000 donors tested one was positive for B19 antigen by counter current immunoelectrophoresis and over 100 ml of undiluted B19 containing material was obtained. However, much of the positive donation was incorporated in a plasma pool of 28 donations. An acid dissociation technique was used to recover B19 antigen from immune complexes formed in the plasma pool.

Antigens, Viral↗
PubMed1990

Screening plasma donors for high-titre antibody to cytomegalovirus using a latex agglutination test.

Cytomegalovirus (CMV) can cause severe morbidity in immunosuppressed patients. Regional transfusion centres in the UK are required to supply high-titre anti-CMV plasma to the Blood Products Laboratory (BPL), now called 'Bio-Products Laboratory', for the production of specific intravenous immunoglobulin at the Protein Fractionation Centre in Scotland. For this purpose, 703 plasmapheresis donors were screened by a modified latex agglutination test to assess their suitability as donors with high-titre anti-CMV. CMV antibodies were found in 48% of the donors. Seropositivity increased with age ranging from 33% in the 20- to 29-year age group to 57% in the 40-49 age group, although the 50-59 age group showed a slight decline to 53%. In all age ranges except the 40-49 group, seropositivity was highest in the female population. With the latex test, 14% of the total donors screened had a titre greater than or equal to 1 in 64, 7% greater than or equal to 1 in 128 and 4.2% greater than or equal to 1 in 256. Samples from 18 donors with titres greater than or equal to 1 in 128 were sent to BPL and all samples were found to have a sufficiently high titre for the production of CMV immune plasma. For BPL the 'cut-off' level for CMV immune plasma is a titre greater than or equal to 1 in 64 by complement fixation. Since the establishment of a panel of donors with high-titre anti-CMV plasma, more than 10 kg of plasma are dispatched monthly from our centre to BPL.

Adult↗
PubMed1990

Use of a bacterial sampler for rapid transfer of microvolumes into microplates.

A method has been devised to transfer very small volumes of serum from microplates prepared during routine screening of blood into microplates containing diluent. Simultaneous transfer of 96 samples is achieved without the need for disposable tips, while still avoiding carry-over between different plates. Using this method a mean transfer volume of 0.9 microliters (cv 8.9%) was obtained, which lent itself conveniently to testing for high-titre anti-microbial antibodies for which high dilution factors are required.

Humans↗
PubMed1990

Recombinant-based competitive anti-HIV assay: solution of some operating problems.

Using the Wellcozyme anti-HIV recombinant assay at 47 degrees, a strongly reactive result with an anti-HIV positive serum sample could not be reproduced when the corresponding plasma sample was used. Dilution in anti-HIV negative serum or kaolin treatment of the plasma specimen produced the clear reactivity seen with the serum sample, and a reduction in incubator temperature was also found to reduce this 'plasma effect'. Problems were also encountered initially when haemolysed serum or plasma with non-standard concentrations of anticoagulant were tested. These phenomena were not apparent when the same manufacturer's test based on cell-derived antigen was used, indicating that the introduction of new technology may cause unforeseen problems although these can usually be overcome.

AIDS Serodiagnosis↗