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Biomedical subjects

P Metcalfe

Publications and source records attributed to P Metcalfe.

At least 55 records · Page 3Linked to original sources
PubMed1995

Human platelet antigen-2 and -3 genotyping by PCR-SSP.

Allele-specific PCR using sequence specific primers (PCR-SSP) is a simple and reliable technique to detect point mutations in genes. We have developed a PCR-SSP to enable the detection of a C-T mutation at position 482 of the GPIb gene and a T-G mutation at position 13,962 in exon 26 of the GPIIb gene. These point mutations are at the basis of the HPA alloantigens 2a, 2b and 3a, 3b respectively. One primer of each primer set has a 3' nucleotide complementary to the DNA sequence coding for one allele. PCR product is only produced when the corresponding DNA is present and thus the genotype is determined by the presence or absence of a band in agarose electrophoresis of PCR products. A second set of primers in the same reaction yields a product regardless of the HPA genotype to control the efficiency of the PCR amplification. The HPA-2 and -3 genotypes determined in this way were in strict concordance with those established by conventional genotyping using PCR followed by restriction enzyme digestion (PCR-ASRA). PCR-SSP is a rapid and reliable technique that can be used for the determination of alleles which code for platelet alloantigens.

Antigens, Human Platelet↗
PubMed1995

The Windsor Clinic Alcohol Withdrawal Assessment Scale (WCAWAS): investigation of factors associated with complicated withdrawals.

A new scale for measuring the severity of the alcohol withdrawal syndrome has been developed. The Windsor Clinic Alcohol Withdrawal Assessment Scale (WCAWAS) has more objective criteria than its parent scales and has high inter-rater reliability and concurrent validity. This article describes the development of the WCAWAS and its use in an investigation of which factors were associated with complicated withdrawals in 142 consecutive patients admitted for detoxification. Multivariate analyses showed that drinking behaviour variables and MCV were successful at predicting complicated withdrawals. The WCAWAS was not successful at predicting which patients developed convulsions. Further studies are required to see if the WCAWAS is more successful at predicting which patients will develop visual hallucinations. The WCAWAS is useful as a teaching aid and in following the clinical course of patients and their response to treatment.

Adult↗
PubMed1994

A simplified method for large-scale HPA-1a phenotyping for antenatal screening.

A simplified method for large-scale HPA-1a phenotyping of platelets was developed for use in an antenatal screening programme for fetomaternal alloimmune thrombocytopenia (FMAIT). The test was based on the MAIPA assay, which was modified for antigen-typing with a well-characterized anti-HPA-1a reagent. The resulting assay gave reliable results, was inexpensive and allowed testing of large batches using semiautomated equipment.

Antibodies, Monoclonal↗
PubMed1994

Relative importance of immune and non-immune causes of platelet refractoriness.

In this prospective study, 26 consecutive patients being treated for haematological malignancies receiving standard (i.e. non-leucocyte-depleted) blood components were observed for the development of refractoriness to platelet transfusions. One hundred and sixteen of the 266 (44%) platelet transfusions failed to produce a satisfactory response. In 102/116 (88%), the poor response was in the presence of non-immune factors known to be associated with platelet refractoriness. Non-immune factors were present alone in 78/116 (67%), and in combination with immune factors in a further 24/116 (21%). Immune factors (HLA and platelet-specific antibodies) were present during 29/116 (25%) of unsuccessful platelet transfusions. Statistical analysis confirmed that platelet refractoriness was significantly associated with the presence of non-immune factors. The non-immune factors associated with refractoriness were often multiple, most frequently a combination of fever, infection and antibiotic therapy. This study provides evidence that immune mechanisms were not the predominant cause of platelet refractoriness in the patient population studied. It also suggests that measures for the prevention of HLA alloimmunisation, such as leucocyte depletion, may have a limited impact in reducing the incidence of refractoriness to platelet transfusions.

Acute Disease↗
PubMed1993

Antenatal management of severe feto-maternal alloimmune thrombocytopenia: HLA incompatibility may affect responses to fetal platelet transfusions.

In feto-maternal alloimmune thrombocytopenia (FMAIT), severe hemorrhage, particularly intracranial haemorrhage (ICH), may occur before delivery. Management strategies to prevent ICH in high-risk pregnancies include maternal administration of intravenous Ig with or without steroids and fetal platelet transfusions. This report describes a patient who lost three fetuses with ICH because of FMAIT due to anti-HPA-1a. ICH occurred earlier in successive pregnancies (at 28, 19, and 16 weeks of gestation) despite maternal treatment with intravenous Ig and steroids from 14 weeks of gestation in the third pregnancy. The fourth pregnancy was managed by administering weekly intraperitoneal injections of Ig to the fetus from 12 to 18 weeks of gestation. At 18 weeks, there was no evidence of ICH, but the fetal platelet count was only 12 x 10(9)/L. Serial fetal platelet transfusions were started, but there were poor responses because of immune destruction of the transfused platelets by maternal HLA antibodies. There were improved responses to transfusions prepared from the mother and from HLA-compatible HPA-1a-negative donors. At 35 weeks of gestation, a normal infant was delivered by Caesarean section after 20 platelet transfusions. There was prolonged thrombocytopenia in the baby for 15 weeks after birth, probably due to transfer of HPA-1a antibodies in the transfusions of unwashed maternal platelets. The optimal management of pregnancies likely to be severely affected by FMAIT is still evolving. Intensive management was successful in this case, but a successful outcome cannot be guaranteed in severely affected cases. This is the first time that HLA incompatibility has been found to complicate fetal transfusion therapy.

Adult↗
PubMed1993

Investigation of the tissue equivalence of gels used for NMR dosimetry.

The transition of Fe2+ to Fe3+ in Fricke solution after irradiation results in a change of NMR proton relaxation times in agarose gels which can be used for the dosimetry of ionizing radiation. The main advantage of this system is the possibility of observing dose distributions in 3 dimensions in a medium which is supposed to be tissue equivalent. The aim of the present study was to quantify parameters which determine the tissue equivalence of NMR dosimetry gels. Electron densities and effective atomic numbers were calculated for gels with varying iron, sulphur and agarose concentration. The Hounsfield CT numbers so derived agree well with the CT numbers measured on a clinical CT scanner (effective photon energy 70.7 keV). The Hounsfield CT number of 7.2 +/- 1.5 (n = 9) measured for a 1.5% agarose gel doped with 0.5 mM ammonium ferrous sulphate and 125 mM sulphuric acid compares well with the calculated one of 8 +/- 5. Relaxation times were measured from a series of MR images obtained on a 1.5 T clinical MR scanner. The observed change in 1/T1 of the gel with dose was found to be linear up to 10 Gy (0.084 s-1 Gy-1). No difference in dose response for 10 Gy delivered by four different superficial radiation qualities (HVT = 1.4-7.5 mm Al) could be observed. These findings and the calculated effective atomic number of 7.46 demonstrate the close tissue equivalence of this agarose gel which makes it an ideal tool for the investigation of low energy therapeutic x-rays.

Ferrous Compounds↗
PubMed1993

HPA-1 typing by PCR amplification with sequence-specific primers (PCR-SSP): a rapid and simple technique.

A DNA-based method was developed to genotype donors for the human platelet antigens HPA-1a and -1b. Sequence-specific primers (SSP) were used in the polymerase chain reaction (PCR) which allowed the HPA-1a/1a, -1b/1b and -1a/1b genotypes to be determined by PCR alone, no second analytical stage was required. 10 donors were tested by PCR-SSP and the results were concordant with serological phenotyping and independent DNA analysis.

Antigens, Human Platelet↗
PubMed1993

Readout of thermoluminescence dosimetry chips using a contact planchet heater.

Thermoluminescence dosimetry (TLD) is performed in many radiotherapy departments using LiF chips which are evaluated by means of a contact heater. The aim of the present study was to investigate the influence of the TL chip position on the heating planchet and to study the self absorption of light in the chips during readout. Experiments were performed using standard LiF chips (3.1 x 3.1 x 0.89 mm3) on a circular heating planchet with a diameter of 13 mm. A two step readout cycle (10s 160 degrees C, 10s 300 degrees C) was used and the integral under the luminescence curve during the second step evaluated. Moving the chip away from the centre of the planchet without adjusting the temperature cycle leads to a peak broadening which can result in a signal loss of up to 40%. The use of a purpose build positioning device tended to improve the reproducibility of the readings. Self absorption of light in a normal chip on the heating planchet was studied by exposing chips in the strong dose gradient of the build up region of a 18 MV X-ray beam. The dose throughout the chip was investigated using a stack of 0.14 mm thick chips. In a 5 x 5 cm2 field the dose varied from 7% at the surface facing the beam to 23% at the opposite side of the chip. Reading the chips with the side facing the beam up in the reader resulted in a 1.9% smaller dose reading than with the chips upside down.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermoluminescent Dosimetry↗
PubMed1992

Neonatal alloimmune thrombocytopenia due to anti-P1A1 (anti-HPA-1a): importance of paternal and fetal platelet typing for assessment of fetal risk.

Neonatal alloimmune thrombocytopenia (NAIT), which usually involves sensitization to P1A1 (HPA-1a), may have devastating complications for the fetus. These may be prevented by antenatal treatment of severe cases with either maternally administered high-dose gamma-globulin and/or repeated intrauterine platelet transfusions. Determination of the paternal platelet phenotype is useful for counseling parents who have had one or more affected pregnancies. This report of an unaffected pregnancy in a woman with a history of previous pregnancies complicated by NAIT illustrates the role of paternal and fetal platelet phenotyping in managing existing pregnancies at risk of NAIT.

Adult↗
PubMed1990

Management of fetal alloimmune thrombocytopenia by weekly in utero platelet transfusions.

Alloimmune neonatal thrombocytopenia (ANT) may cause intracranial haemorrhage in utero as well as at delivery. Recent management has concentrated on attempts to minimise fetal thrombocytopenia and prevent its complications. This report describes further experience with the use of repeated intravascular transfusions of compatible platelets in utero. The patient studied had already had one infant with intracranial haemorrhage due to ANT. In her next pregnancy, weekly intra-uterine platelet transfusions were given from 26 weeks, but intra-uterine death occurred at 30 weeks after the mother had a heavy fall. In her most recent pregnancy, weekly intravascular transfusions of platelets were given by cordocentesis from 29 to 34 weeks. The fetal platelet count was maintained above 30 X 10(9)/l for almost all of the last 6 weeks of pregnancy before delivery of a normal infant by Caesarean section at 35 weeks' gestation. This approach is effective in preventing severe fetal thrombocytopenia in the last trimester of pregnancy and is contrasted with alternative treatments of ANT. Further data are required to determine the efficacy and risks of these treatments.

Blood Transfusion, Intrauterine↗
PubMed1990

Report on the fourth ISBT/ICSH platelet serology workshop (London 1988).

The fourth ISBT/ICSH platelet serology workshop took place in 1988. It consisted of a wet workshop carried out by the 17 participating laboratories during March 1988, followed by a discussion of the results at a meeting of the ISBT/ICSH Expert Panel on Platelet Serology at the ISBT/BBTS Congress in London in July 1988. Sixteen samples, including 1 negative control serum, were analysed by the participants using methods of their choice. There was general agreement on 10/16 samples. The results indicated progress in the following areas: (i) antibody identification; (ii) differentiation of platelet-specific and HLA antibodies; (iii) glycoprotein localisation of platelet specific antigens; (iv) identification of new platelet antigen systems.

Blood Grouping and Crossmatching↗
PubMed1989

Intravenous immunoglobulin therapy in thrombocytopenic infectious mononucleosis.

Severe haemorrhagic thrombocytopenia in infectious mononucleosis with positive Epstein-Barr virus (EBV) serology remains a threatening clinical problem. Although rare, fatalities have been reported. We present clinical, haematological and serological details of two patients with diffuse bleeding associated with this disease who failed conventional steroid treatment and who both responded promptly and effectively to infusions of intravenous immunoglobulin (i.v. Ig). A platelet immunofluorescence test was used to detect platelet antibodies in acute and recovery phase patient sera against autologous recovery platelets and against normal allogeneic group O platelets. In one patient, indirect immunofluorescence using recovery platelets detected an IgG platelet autoantibody with acute phase autologous serum. No platelet antibody was detected in the second patient. The data presented demonstrate that response to i.v. Ig is independent of serological detection of platelet autoantibodies. Therapy with i.v. Ig should be considered in any case of haemorrhagic thrombocytopenia associated with EBV infection shown to be refractory to steroid treatment.

Adult↗
PubMed1987

Disappearance of HLA and platelet-specific antibodies in acute leukaemia patients alloimmunized by multiple transfusions.

Alloimmunization by platelet transfusions was studied in 154 patients with acute leukaemia. 17 patients had HLA antibodies at initial presentation induced by previous transfusions or pregnancies; one of these also had platelet-specific antibodies and one other patient had platelet-specific antibodies alone. A further 38 patients developed HLA antibodies during therapy; three also had platelet-specific antibodies and two patients developed platelet-specific antibodies alone. Of these, 37 patients with HLA antibodies including three with platelet-specific antibodies and one patient with platelet-specific antibodies alone survived their initial therapy and formed the basis of this study. Antibodies once detected persisted throughout the study in seven of the 37 patients with HLA antibodies including one patient with platelet-specific antibodies and in the patient with platelet-specific antibodies alone. HLA antibodies disappeared after discontinuation of transfusions in six patients, and after switching to HLA matched platelet transfusions and leucocyte-poor blood in eight patients; two of the latter patients also had platelet-specific antibodies which disappeared. The other 16 patients with HLA antibodies lost their antibodies despite continued transfusions.

Acute Disease↗
PubMed1987

Incidence and mechanism of neutropenia and thrombocytopenia in patients with human immunodeficiency virus infection.

The incidence of lymphopenia, thrombocytopenia and neutropenia was studied in 105 homosexual men with HIV infection. Lymphopenia was common in patients with AIDS (75%), but its incidence in PGL (24%) was not significantly different from that in asymptomatic anti-HIV positive (15%) homosexual men. Neutropenia and thrombocytopenia were found in patients with AIDS or PGL, but not in asymptomatic anti-HIV positive homosexuals. The study suggests that the neutropenia and thrombocytopenia in these patients were due to autoimmune destruction of neutrophils and platelets.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Post-transfusion purpura associated with anti-Baka and anti-PIA2 platelet antibodies and delayed haemolytic transfusion reaction.

The occurrence of post-transfusion purpura (PTP) in a 16-year-old girl with sickle/beta-thalassaemia is described. Clinically this was a typical case of PTP, but it was unusual serologically. Anti-Baka and anti-PIA2 platelet-specific antibodies were identified and the patient's platelets were typed as homozygous PIA1-positive and Baka-negative. The patient also developed red-cell, granulocyte and lymphocytotoxic antibodies in response to the blood transfusion and had a delayed haemolytic transfusion reaction.

Adolescent↗