Biomedical subjects
J A Barbara
Publications and source records attributed to J A Barbara.
Routine blood donor screening for syphilis can reveal recent infection.
Explore the source record for details and available documents.
Questions of quality: how much HBsAg is there in this sample and is our assay sensitive enough to detect it?
Explore the source record for details and available documents.
Significance of p24 on immunoblot with a negative anti-HIV ELISA result.
Explore the source record for details and available documents.
Polymerase chain reaction and transfusion microbiology.
Polymerase chain reaction (PCR) involves alternate denaturing and re-annealing of DNA in test samples in the presence of appropriate oligonucleotide primers complementary to opposite strands of the target DNA together with a heat-stable DNA polymerase, Mg2+ and the four nucleotide triphosphates. DNA target segments can be 'amplified' ten-millionfold by 25-35 such cycles. Even greater amplification (approximately 10(12)-fold) with enhanced specificity can be obtained by a second set of amplification cycles using a further pair of 'nested' primers sited within the DNA sequence defined by the original primers. PCR can be applied to the study of the whole range of transfusion-transmitted infections, both plasma and cell associated; RNA viruses can be analyzed if a DNA copy is made from the viral RNA by treatment with reverse transcriptase. In a transfusion context, the retroviruses (HIV-1, HIV-2, HTLV-I, HTLV-II), HCV and HBV have been the viruses most intensively subjected to PCR analysis. The advantages of PCR in this context include its ability to detect virus during the 'window period' or seronegative stages of infections and its value as a marker for viraemia and for the detection of viruses in products made from large pools of plasma. True immunity may also be differentiated from persistent infection in the presence of antibody. Similarly, PCR can overcome problems of diagnosis of acute infection caused by the presence of passively transferred antibody. Detailed strain differentiation is also possible by PCR, in conjunction with sequencing or with the aid of restriction endonucleases.(ABSTRACT TRUNCATED AT 250 WORDS)
Candida albicans arthritis in a renal allograft recipient with an interaction between cyclosporin and fluconazole.
Explore the source record for details and available documents.
Screening blood donations for HCV.
Explore the source record for details and available documents.
Diagnostic reagents for hepatitis C virus.
The development of diagnostic methods for hepatitis C virus is presented. Special attention is paid to the selection of antigenic markers, the type of assay selected and the interpretation of results. A few of the pitfalls and ambiguities of various assays are discussed and possible future methods are described.
Post transfusion septicaemia 1980-1989: importance of donor arm cleansing.
AIMS: To determine the prevalence of Pseudomonas fluorescens on the arms of blood donors, and to elucidate one possible cause for its predominance (60% of cases during 1980-89) in exogenous post transfusion septicaemia (PTS). METHODS: Skin swabs were taken from the arms of 782 blood donors and cultured on to heated blood agar. After incubation, Oxidase reagent and the Gram stain were used to select non-fermentative Gram negative rods, which were then subcultured and identified using the Analytical Profile System (API) 20 NE system. RESULTS: Non-fermentative Gram negative rods were found on the arms of 11.7% of donors, Pseudomonas spp on 1.0%, and Ps fluorescens on the arms of 0.3% of donors. CONCLUSIONS: This evidence emphasises the absolute requirement for efficient skin cleansing of blood donors' arms to minimise the risk of exogenous PTS.
Anti-HBs detection: a modified passive haemagglutination assay.
Modification of a commercial haemagglutination assay for the detection of anti-HBs has reduced the test time from over one hour to approximately 25 min. increased sensitivity ten-fold without any prozoning, maintained specificity and reduced costs by 90%. The modification consists of diluting the reagent cells ten-fold; these are then added to dilutions of test serum in a V-well microplate. After incubation, plates are centrifuged and then inclined at 70 degrees. Positive and negative reactions can be clearly distinguished within approximately 10 minutes.
Membranous nephropathy with graft-versus-host disease in a bone marrow transplant recipient.
A 43-year-old man developed the nephrotic syndrome 26 months after allogeneic bone-marrow transplantation for chronic myeloid leukemia. This occurred during an exacerbation of graft-versus-host disease (GVHD) and both problems remitted after therapy with cyclosporine and prednisolone. Renal biopsy showed ultrastructural and immunofluorescence evidence of membranous nephropathy. Anti-nuclear antibodies (but not antiglomerular or anti-renal tubular epithelial antibodies) were detected in his serum. Experimental GVHD in mice has been associated with immune complex glomerulonephritis and the presence of IgG autoantibodies which has been attributed to abnormal T (donor)/B (recipient) cell co-operation. This association can be extrapolated to the human GVHD where autoantibody formation is better described than immune complex glomerulonephritis.
Hepatitis A virus, blood donors, and immunoglobulin preparations.
Explore the source record for details and available documents.
Low incidence of non-A, non-B post-transfusion hepatitis in London confirmed by hepatitis C virus serology.
To see whether the introduction of screening tests for post-transfusion non-A, non-B hepatitis (NANBH) in the UK would be worth while, the incidence of such hepatitis was assessed among patients receiving blood during operations at five hospitals served by the North London Blood Transfusion Centre. 387 patients, who each received blood or blood components from an average of 3 donors were followed up prospectively and blood samples were taken every 2 weeks for 3 months and then each month for a further 3 months. 229 patients also provided a sample at 12 months. All available patient and donor samples were tested for alanine aminotransferase concentrations and for antibody to hepatitis C virus (anti-HCV) by ELISA. Repeatedly anti-HCV positive samples were submitted to supplementary HCV assays. 1 of the 387 patients showed biochemical evidence of acute post-transfusion NANBH after exclusion of non-viral causes. Anti-HCV developed in this patient and the seroconversion was confirmed by recombinant immunoblot assay and polymerase chain reaction. Serum from 1 of the 8 donors whose blood he received was positive for anti-HCV by all three methods. In another patient HCV seroconversion was shown by ELISA but alanine aminotransferase concentrations remained normal throughout follow-up. His samples and those of his 2 donors were negative for HCV by the polymerase chain reaction. A third patient showed rises in alanine aminotransferase compatible with post-transfusion NANBH, but serology and polymerase chain reaction assays for HCV were negative for her samples and those of her donors. Anti-HCV reactivity likely to be false positive (negative by both confirmatory tests and no adverse effects in recipients) was seen in 6 of 1283 donors. This study, despite its being carried out in the part of the UK with the highest frequency of infectious markers in blood donations, has shown a very low incidence of post-transfusion NANBH.
A comparison of four enzyme immunoassays for the simultaneous detection of HIV-1- and HIV-2-specific antibody.
The performance of four HIV 1 and 2 combined assays has been compared with current type-specific assays using three panels of sera. The first panel comprised single samples from 19 HIV-1-infected persons; the second panel comprised 19 sera from 16 HIV-2-infected persons. Samples from both these panels were titrated across interpolated end points of detectability. The third panel comprised sera from 5200 consecutive blood donors. The four combined assays, manufactured by Abbott Laboratories, Behring Laboratories, Diagnostics Pasteur and Wellcome Diagnostics Laboratories detected all anti-HIV-1 sera at high dilution; the immunometric assay from Wellcome was particularly proficient. All assays were broadly similar in their ability to detect sera from recently infected persons. The same assays were also effective in detecting anti-HIV 2 in sera both from seropositive individuals and from a single recently-infected person, though none was as sensitive as an inhouse competitive EIA. When used for donor screening the repeat reactive rates for donors negative for HIV 1 and 2 antibodies ranged between 1.80% for Elavia Mixt from Pasteur, 0.27% Abbott combined and 0.15% for the Wellcome combined assays.
Post-transfusion NANBH in the light of a test for anti-HCV.
The incidence of post-transfusion hepatitis (PTH) varies over an order of magnitude in different parts of the world. For example, prospective studies from Spain and the UK reveal rates of PTH of approximately 10 and 0.5% respectively. Similarly the association of a history of transfusion in patients with chronic liver disease varies widely; in Japan, with high rates of PTH, the association appears obvious whereas in the UK less obvious. These factors must be taken into account when assessing the cost-effectiveness of pre-transfusion screening for anti-HCV. A useful approach to assessing the value of screening donors for anti-HCV is to study prospectively the correlation of anti-HCV and PTH. In carefully selected cases of PTH, the correlation of anti-HCV and PTH in donor-recipient sets of samples may be very high. However, the predictive value of 'first-generation' assays for anti-HCV in routine studies of unselected cases of PTH may be less than 20% in countries with low rates of transfusion-transmitted non-A, non-B hepatitis (NANBH). The anti-HCV screening tests and supplementary assays are continually evolving. More recent assays incorporate structural as well as non-structural antigens in both types of ELISA used for screening and in the supplementary tests such as the recombinant based immunoblots.(ABSTRACT TRUNCATED AT 250 WORDS)
Antibody to hepatitis C virus in blood donors found positive for other agents. I. Treponemal infection.
Stored serum samples from 169 blood donors found positive for TPHA were tested for antibodies to hepatitis C virus (anti-HCV) and to hepatitis B core (anti-HBc), as evidence of previous HBV infection, a condition known to be sexually transmissible. Only three donors were positive with a 'first generation' anti-HCV and all three failed to confirm with a recombinant immunoblot assay (RIBA). In contrast, 33 (19.5%) of the TPHA-positive donors were positive for anti-HBc. The results suggest that sexual transmission is not a major factor in the spread of HCV.
Antibody to hepatitis C virus in blood donors found positive for other agents. II. Anti-HIV-1.
Stored serum samples from 24 blood donors confirmed positive for anti-HIV-1 were tested for antibody to hepatitis C virus (HCV). Those repeatedly reactive using the anti-HCV ELISA screening test were retested by the HCV recombinant immunoblot (RIBA). Risk-factors for the contraction of HIV infection that had been elicited at formal counselling sessions were evaluated in relation to HCV/HIV modes of infection. The only two donors confirmed to be anti-HCV positive both admitted to intravenous drug use.
Is there a wastage of resources due to non-specificity of anti-HIV ELISAs?
A library of anti-HIV ELISA 'grey-area' and repeatably reactive samples sent for confirmatory testing, were retested using a second technique, the modified (Fujirebio Gelatin Particle) agglutination test (MAT). On testing 224 grey-area reactive samples, only four were found to be reactive with this second test. On retesting a further 259 ELISA repeatably reactive samples, of which only 33 were confirmed to be anti-HIV-1, only 45 were reactive by MAT; these included the 33 confirmed as positive samples, thereby reducing the false-positive from 226 to 12. The introduction of this second technique supported our decision to cease the referral of grey-area samples. It also demonstrated the high prevalence of non-specificity of repeatable reactivity associated with some of the most specific ELISA kits currently available.