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Biomedical subjects

F E Preston

Publications and source records attributed to F E Preston.

At least 37 records · Page 2Linked to original sources
PubMed2000

Evaluation of a global screening assay for the investigation of the protein C anticoagulant pathway.

We have evaluated a global screening test for the protein C pathway, the 'ProC Global' (Dade Behring Ltd, Milton Keynes, UK). Patient groups tested included inherited protein C or S deficient and inherited/acquired activated protein C resistance. Results showed that protein C deficiencies and activated protein C resistance could be successfully detected with this test whereas deficiencies of protein S were less readily distinguished from the normal population. The ProC Global was unreliable in patients with antiphospholipid antibodies, raised plasma factor VIII:C and in those receiving oral anticoagulant therapy.

Activated Protein C Resistance↗
PubMed2000

Monitoring unfractionated heparin therapy: relationship between eight anti-Xa assays and a protamine titration assay.

Several studies have demonstrated that heparin assays, such as anti-activated factor X (anti-Xa) assays, can be successfully substituted for activated partial thromboplastin time for heparin dosage monitoring. A number of different assays are available and the relationship between results with different techniques is largely unknown. The aim of the present study was to assess the relationship between heparin assays by protamine titration and anti-Xa assays. Samples were collected from 43 patients receiving unfractionated heparin (UFH). In each sample, the heparin level was determined using a protamine titration assay and eight commercially available anti-Xa assays. The mean heparin level by protamine titration was 0.31 U/ml. Mean anti-Xa activity results ranged from 0.40 to 0.42 IU/ml for the three clotting-based assays, and from 0.32 to 0.40 IU/ml for five chromogenic assays. Thus mean results of different anti-Xa assays varied by up to 30%. The range of anti-Xa activity equivalent, on average, to 0.2-0.4 U/ml by protamine titration, considered to be the therapeutic range, was approximately 0.25-0.5 IU/ml, depending on the assay. The relationship between results of clotting and chromogenic methods was similar irrespective of whether or not warfarin-induced prolongation of international normalized ratios was present.

Antibodies↗
PubMed2000

Major structural defects in the antithrombin gene in four families with type I antithrombin deficiency--partial/complete deletions and rearrangement of the antithrombin gene.

The molecular basis of quantitative antithrombin deficiency was investigated in four families predicted to have major antithrombin gene rearrangements. A 1,442 bp deletion and insertion of the sequence 5'T(n = 38-40)GAGACG was characterised in one case. Sequence surrounding the breakpoints contained two perfect, and one imperfect, inverted repeats which may have mediated formation of a stem loop structure on one strand during DNA replication potentiating the deletion. A 9,219 bp deletion spanning introns 2 to 5 was identified in a second family. The identical 6 bp sequence was upstream of each breakpoint and the 5' breakpoint was located in a sequence of the Alu 3 repeat predicted to be susceptible to strand breakage during transcription. This may have promoted misalignment, and deletion, of one of the repeats and the intervening DNA. A novel 1.8 kb antithrombin gene fragment was present in DNA digests from affected members of the third family suggesting a partial antithrombin gene duplication event while in the remaining family, evidence supporting a complete gene deletion was obtained.

Adolescent↗
PubMed2000

Recombinant VIIa concentrate in the management of bleeding following prothrombin complex concentrate-related myocardial infarction in patients with haemophilia and inhibitors.

Prothrombin complex concentrates (PCCs) and, more recently, activated prothrombin complex concentrates (APCCs), are widely used for the treatment of active bleeding in haemophiliacs with inhibitors. Myocardial infarction (MI), associated with the use of these concentrates, is a well-recognized, but uncommon, complication. We review the 14 previous cases published in the literature and describe two additional patients. MI related to the use of activated and non-activated PCCs predominantly affects young patients who often have no preceding history of, or risk factors for, MI and tends to be associated with large cumulative doses of concentrate. The most frequent pathological finding is myocardial haemorrhage, with no evidence of coronary artery atheroma or thrombosis. The management of further bleeding in these patients is difficult. We have safely used recombinant factor VIIa to treat bleeding in the immediate and long-term period following PCC-related MI.

Abdomen↗
PubMed1999

A rapid method for haemophilia B mutation detection using conformation sensitive gel electrophoresis.

Conformation sensitive gel electrophoresis (CSGE) was confirmed as an effective procedure for screening the factor IX (FIX) gene by detecting 10/10 previously known FIX gene mutations. The FIX genes of a further 11 haemophilia B patients with unknown mutations were then screened and an abnormal CSGE profile was identified in all cases. Subsequent DNA sequencing demonstrated one of these to be a novel mutation (31133insT, Arg338Fs), the remaining 10 having been previously reported on the haemophilia B database. Mutation screening of the FIX gene using CSGE was demonstrated to be a rapid and efficient means of carrier analysis in families with haemophilia B.

Electrophoresis, Agar Gel↗
PubMed1999

Lipid composition of seven APTT reagents in relation to heparin sensitivity.

The phospholipid content of different activated partial thromboplastin time (APTT) reagents was determined and compared to heparin sensitivity. The seven reagents included were those most widely used amongst participants of the U.K. National External Quality Assessment Scheme (NEQAS) at the time of study. Heparin sensitivity was assessed using the APTT ratios obtained by more than 300 NEQAS participants on five plasmas prepared from patients receiving unfractionated heparin. The concentrations of three neutral lipids and six phospholipids present in the seven APTT reagents were determined by high-performance thin-layer chromatography (HPTLC) and densitometry. Both the concentrations and the relative percentages of individual phospholipid components varied markedly between reagents. The total phospholipid concentration included a 12-fold range from 16 to 205 microgram/ml. Phosphatidylserine (PS) was completely lacking from one reagent prepared from vegetable material and ranged from 3 to 22 microgram/ml in the other six reagents containing extracts from animal tissue. The concentration of phosphatidylcholine ranged from 3 to 109 microgram/ml. There was no demonstrable relationship between the concentration of any individual lipid components and heparin sensitivity. However, the relative percentage phospholipid composition was important since a lower % of PS or phosphatidylinositol (PI) correlated with increasing heparin sensitivity.

Anticoagulants↗
PubMed1999

Spinal epidural haematoma in haemophilia A with inhibitors--efficacy of recombinant factor VIIa concentrate.

We report the case of a 21-year-old man with severe haemophilia A and factor VIII inhibitors who presented with an extensive spinal epidural haematoma (C2-T12), probably induced by sit-up exercises. The bleed was defined by magnetic resonance imaging of the cervical and thoracic spine and prompt treatment with recombinant factor VIIa concentrate led to complete resolution at 4 weeks. Neurological sequelae were averted and surgical decompression was not necessary. We discuss the difficulties in diagnosis and management of such a case.

Adult↗
PubMed1999

Standardization of prothrombin time for laboratory control of oral anticoagulant therapy.

Laboratory monitoring of oral anticoagulants is mandatory to ensure efficacy and safety of therapy. The test of choice is the prothrombin time (PT), using thromboplastins, which vary markedly in respect of the defect induced by oral anticoagulants. Standardization is improved by the use of the WHO calibration model for thromboplastins. This system defines the International Sensitivity Index (ISI) of a reagent in relation to a reference material. This is then used together with a locally determined mean normal PT to derive the International Normalized Ratio (INR). There is an inverse relationship between sensitivity and ISI, the lower the ISI the greater is the sensitivity of the reagent. There are important practical advantages to using a sensitive reagent with ISI of 1.2 or less. The ISI system was originally designed for manual tests and in some cases the ISI is influenced by the use of coagulometers, which generally have the effect of lowering the ISI. For this reason the ISI should be assigned for the combination of reagent and endpoint detection system. A thromboplastin should not be used with techniques for which the ISI is unknown. In some instances there is variation between instruments of the same type, in which case a local calibration using plasma calibrants with assigned values can be considered. The precise requirements for such local calibrations are presently the subject of research in a number of centers. The INR/ISI system is increasingly being adopted in many countries for anticoagulant therapy. Some past difficulties leading to discrepancies between results with different reagents have now been resolved and the view that this is the best available system for standardization of the PT for monitoring oral anticoagulants is widely held.

Administration, Oral↗
PubMed1999

Mesenteric infarction due to combined protein C deficiency and prothrombin 20210 defects.

The prothrombin gene mutation, 20210A, a guanine to adenine substitution at nucleotide position 20210, has recently been described as an additional risk factor for venous thromboembolic disease. We describe the case of a patient with combined heterozygous prothrombin 20210A mutation and type 1 protein C deficiency who presented with massive mesenteric venous infarction of his small bowel and survived following the use of protein C concentrate and extensive small bowel resection.

Anticoagulants↗
PubMed1999

A common splice site mutation is shared by two families with different type 2N von Willebrand disease mutations.

Using an ELISA-based method to detect type 2N von Willebrand disease (VWD), we found two individuals with absent FVIII binding. Direct sequencing of the FVIII binding region of the von Willebrand factor (VWF) gene showed that one individual had an R854Q substitution whilst the other had a T791M substitution. The very low FVIII binding and the VWF:Ag levels in both individuals suggested a second defect on the other VWF allele. Conformation sensitive gel electrophoresis of polymerase chain reaction amplified DNA was used to detect an additional change in the VWF gene of each patient. Direct sequencing confirmed a previously unreported G to A transition in the donor splice site in intron 25 of both individuals which should result in a null allele. This was confirmed by mRNA analysis. These two individuals therefore have compound heterozygous VWD in which the only expressed allele has a type 2N mutation. In our population, such compound heterozygosity appears to be a significant cause of type 2N VWD.

Alleles↗
PubMed1999

Anti Xa monitoring during treatment with low molecular weight heparin or danaparoid: inter-assay variability.

If laboratory monitoring of low molecular weight heparin (LMWH) therapy is required the test of choice is the anti Xa activity assay. The relationship between anti Xa results obtained using different techniques is unknown. The aim of the present study was to compare anti Xa results obtained with eight different commercially available anti Xa activity assays (five chromogenic and three clotting based assays) in samples from patients receiving either therapeutic or prophylactic LMWH (enoxaparin or dalteparin) or danaparoid. We have demonstrated that highly significant differences exist between results obtained using different techniques. The mean anti Xa activity in patients receiving treatment or prophylaxis with enoxaparin ranged from 0.28 to 0.64 iu/ml. A similar relationship was present in samples from patients treated with dalteparin, mean anti Xa results ranging from 0.43 to 0.69 iu/ml. The Heptest clotting assay as used here in combination with the Automated Coagulation Laboratory instrument, was associated with lower results than other clotting or chromogenic techniques. In patients receiving danaparoid for heparin induced thrombocytopaenia (HIT) mean results with three clotting based assays were 0.30 to 0.36 u/ml, compared to mean results of 0.47 to 0.65 u/ml for chromogenic assays. Our data clearly indicate that the selection of anti Xa assay method could influence patient management since the dose required to achieve the therapeutic range would differ according to the assay employed. This is particularly important since the frequency of haemorrhagic side effects has been shown by others to be dose dependent, irrespective of the concomitant anti Xa activity results. In danaparoid therapy the clotting assays studied here should not be employed for monitoring without a modified target range, unless it can be demonstrated that the higher doses required to achieve the therapeutic range are safe.

Antibodies↗
PubMed1999

Local calibration of international normalised ratio improves between laboratory agreement: results from the UK National External Quality Assessment Scheme. UK NEQAS (Blood Coagulation) Steering Committee.

In the present study we have performed local calibration of International Normalised Ratio (INR) measurement systems in a large series of laboratories. We assigned INRs to five lyophilised plasma calibrants, one prepared from normal plasma and four using plasma from warfarinised patients, using different International Reference Preparations for Thromboplastin. These five calibrants, and two lyophilised test plasmas were analysed by 349 centres using 60 different thromboplastin instrument combinations. Plasma calibrants were assigned INRs using the WHO reference thromboplastin RBT-90 or the European reference thromboplastin CRM 149R. Each participating centre determined PTs of the calibrants with their local system. These PTs were then used to construct a local calibration graph relating PT to INR. The PTs of test plasmas were converted directly into INR using the local calibration model and into INR using the conventional method. The overall medians of conventionally derived INRs of two test plasmas analysed in 349 centres were 2.50 and 3.10, compared to 2.47 and 3.04 after local calibration where RBT-90 was employed to assign INRs to calibrants. Use of CRM 149R to assign INRs to calibrants led to a significant (p<0.0001) increase in INR to 2.7 and 3.36 respectively. When results were grouped according to the thromboplastin employed, agreement between results with different reagents was improved by local calibration. There was a significant reduction (p<0.01) in the spread of results in different centres as indicated by a reduction in coefficient of variation.

Blood Coagulation↗
PubMed1998

Antithrombins Wibble and Wobble (T85M/K): archetypal conformational diseases with in vivo latent-transition, thrombosis, and heparin activation.

The inherent variability of conformational diseases is demonstrated by two families with different mutations of the same conserved aminoacid in antithrombin. Threonine 85 underlies the opening of the main beta-sheet of the molecule and its replacement, by the polar lysine, in antithrombin Wobble, resulted in a plasma deficiency of antithrombin with an uncharacteristically severe onset of thrombosis at 10 years of age, whereas the replacement of the same residue by a nonpolar methionine, antithrombin Wibble, gave near-normal levels of plasma antithrombin and more typical adult thromboembolic disease. Isolated antithrombin Wibble had a decreased thermal stability (Tm 56.2, normal 57.6 degreesC) but was fully stabilized by the heparin pentasaccharide (Tm 71.8, normal 71.0 degreesC), indicating that the prime abnormality is a laxity in the transition of the main sheet of the molecule from the 5- to 6-stranded form, as was confirmed by the ready conversion of antithrombin Wibble to the 6-stranded latent form on incubation. That this transition can occur in vivo was shown by the finding of nearly 10% of the proband's plasma antithrombin in the latent form and also, surprisingly, of small but definitive amounts of latent antithrombin in normal plasma. The latent transition will be predictably accelerated not only by gross mutations, as with antithrombin Wobble, to give severe episodic thrombosis, but also by milder mutations, as with antithrombin Wibble, to trigger thrombosis in the presence of other predisposing factors, including the conformational stress imposed by the raised body temperatures of fevers. Both antithrombin variants had an exceptional (25-fold) increase in heparin affinity and this, together with an increased inhibitory activity against factor Xa, provides evidence of the direct linkage of A-sheet opening to the conformational basis of heparin binding and activation.

Amino Acid Substitution↗
PubMed1998

Norethisterone therapy for bleeding due to gastrointestinal telangiectases in Glanzmann's thrombasthenia.

We report a case of a patient with Glanzmann's thrombasthenia and anti-GPIIb/IIIa alloantibodies who developed life-threatening and intractable bleeding from gastrointestinal telangiectatic lesions. After a period of transfusion-dependent gastrointestinal bleeding despite tranexamic acid, oral iron, omeprazole and platelet transfusions, the use of oral norethisterone produced a significant improvement with a marked reduction in her transfusion requirements.

Adult↗