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Biomedical subjects

C H Toh

Publications and source records attributed to C H Toh.

33 records · Page 2Linked to original sources
PubMed1998

Early identification and prognostic implications in disseminated intravascular coagulation through transmittance waveform analysis.

Efforts to improve the prognosis in disseminated intravascular coagulation (DIC) have been hampered by the lack of an early, useful and rapidly available diagnostic marker. More recently, a characteristic bi-phasic change in the light transmittance waveform profile of the APTT assay has been associated with DIC. In this prospective study, we have assessed the utility of this assay in the routine clinical setting. 1,470 samples were analysed from 747 patients and 41 patients had DIC. The sensitivity and specificity of the bi-phasic waveform pattern for DIC was 97.6% and 98% respectively. The appearance of a bi-phasic waveform preceded the development of abnormalities in the standard laboratory tests for DIC and waveform changes correlated closely with clinical events. In conclusion, transmittance waveform analysis is not only useful as an early diagnostic and single monitoring marker of DIC but the quantifiable and standardisable changes also allow for prognostic applicability in clinical management.

Biomarkers↗
PubMed1997

Evaluation of two simplified methods for genotyping hepatitis C virus.

A number of different approaches have been used for genotyping hepatitis C virus (HCV). Two simplified methods were evaluated, both of which used polymerase chain reaction (PCR) to amplify products from the 5' non-coding region of HCV: non-isotopic restriction fragment length polymorphism (RFLP) analysis and type-specific PCR. Sixty-four viraemic patients suffering from chronic HCV infection were studied using these two techniques; 25/64 samples were further tested with a commercial serotyping ELISA based on synthetic NS4 antigen (Murex, U.K.). The results of the three typing methods were generally in agreement with each other. When only the predominant genotype identified by each method was analysed, the 3 methods had 100% agreement. RFLP did not detect any mixed infections and it was unsuccessful in 16/64 (25%) samples. Both type-specific PCR and serotyping ELISA detected mixed infections. However, serotyping ELISA did not give typeable results in 7/25 (28%) samples, whereas type-specific PCR gave typeable results in all 64 samples. Type-specific PCR detected more mixed infections than serotyping ELISA. Direct sequencing of four PCR products with indeterminate RFLP confirmed changes in restriction enzyme recognition sites. The sequences also confirmed the validity of the predominant genotype in cases of apparent mixed infections. It is possible that some of these cases were artefacts as a result of quasispecies.

Base Sequence↗
PubMed1997

Novel and diagnostically applicable information from optical waveform analysis of blood coagulation in disseminated intravascular coagulation.

Transmittance waveform is the term applied to the optical profile generated from the process of clot formation on standard coagulation tests run on the MDA-180, a new-generation automated coagulation analyser. In patients with disseminated intravascular coagulation, a characteristically abnormal 'biphasic change' is seen on both the activated partial thromboplastin time and thrombin time waveforms. Increasing steepness of the initial slope on the waveform correlates with clinical deterioration and fulminant progression. Although the mechanism underlying the biphasic appearance remains to be elucidated, its identification provides the diagnostic laboratory with a simple, rapid and robust assay for disseminated intravascular coagulation that can help the clinician with urgent and appropriate therapeutic interventions.

Blood Coagulation↗
PubMed1997

Hepatitis G virus RNA and its relation to hepatitis C infection in adult haemophilic patients.

The prevalence of hepatitis C virus (HCV) infection and hepatitis G virus (HGV) RNA were studied in 50 adult haemophilic patients who had received commercial clotting factors prior to 1980. HGV RNA was detectable in 6/ 50 patients (12%); 49/50 (98%) had antibody to HCV and 40/49 (82%) of these were viraemic with detectable HCV RNA; 5/6 patients with detectable HGV RNA had co-existing HCV infection and viraemia. The HGV PCR products from all six patients were directly sequenced and all were shown to be similar to that of HGV but more diverse from that of GB virus C. One patient who had persistent abnormal liver function tests had detectable HGV RNA but no evidence of hepatitis B or C. The presence of HGV RNA in the absence of hepatitis B and C infection indicates that this virus is capable of independent transmission. Independent response to interferon was demonstrated in one patient with co-infection who lost HGV but not HCV after interferon therapy.

Adolescent↗
PubMed1997

Anticoagulants for venous thrombosis.

The anticoagulant agents heparin and warfarin were introduced before the era of randomised clinical trials. As a result, the indications, dosages and monitoring techniques of these drugs have undergone re-evaluation in multiple clinical trials in the past years. Low molecular weight heparin has been developed, which has led to new approaches in anticoagulant management. Current levels of laboratory, pharmacology and clinical knowledge in the treatment of venous thromboembolism are discussed.

Anticoagulants↗
PubMed1994

Use of granulocyte colony-stimulating factor (G-CSF) for mobilizing peripheral blood stem cells: risk of mobilizing clonal myeloma cells in patients with bone marrow infiltration.

Peripheral blood stem cells have been used for autologous reconstitution of haemopoiesis after high dose cytotoxic therapy and produce similar disease response rates as autologous bone marrow transplants. Peripheral blood stem cell transplants are an especially attractive option for patients in whom marrow harvest is not feasible due to bone marrow damage or infiltration. Recombinant growth factors mobilize adequate numbers of stem cells from the marrow but their effect on tumour cell circulation kinetics is not known. We report a patient with multiple myeloma and bone marrow infiltration in whom the use of G-CSF for stem cell mobilization led to release of plasma cells into the peripheral circulation and contamination of the stem cell harvest.

Adult↗
PubMed1993

Activation of protein C and its distribution between its inhibitors, protein C inhibitor, alpha 1-antitrypsin and alpha 2-macroglobulin, in patients with disseminated intravascular coagulation.

Activation and inactivation of protein C during the clinical course of disseminated intravascular coagulation (DIC) was studied in three patients by qualitative (Western blotting) and quantitative (ELISA) analysis and the intensity of procoagulant activity monitored by the measurement of thrombin and factor Xa antithrombin III complexes. In one patient, inhibitor complexes of APC with protein C inhibitor (PCI) and alpha 1-antitrypsin (alpha 1-AT) were observed and the latter predominated at presentation. Both disappeared during the development of remission but the loss of alpha 1-AT complexes preceded PCI complexes which on Western blotting appeared to increase in intensity prior to disappearance. The two other patients bled to death from uncontrollable haemorrhage. In both cases, APC/inhibitor complexes with alpha 2-macroglobulin (alpha 2-M) in addition to PCI and alpha 1-AT were detected and persisted until death. Although PCI appeared to be the primary inhibitor in all three cases, alpha 1-antitrypsin and particularly alpha 2-macroglobulin appeared to assume greater roles in the two fatal cases. These data are similar to previous findings in an experimental animal model of DIC that suggested that alpha 2-macroglobulin and alpha 1-antitrypsin become more important inhibitors of APC as the primary inhibitor PCI is consumed in the face of a sustained procoagulant challenge.

Adult↗
PubMed1993

The generation of thrombin in vivo induces the selective loss of high molecular weight multimers of von Willebrand factor and the reversible sequestration of platelets.

Various levels of thrombin generation were induced by the infusion of a combination of factor Xa (F.Xa) and phosphatidylcholine/phosphatidylserine (PCPS) vesicles into normal dogs and non-human primates. In the dog, an immediate loss of von Willebrand factor antigen (vWF:Ag) with a progressive recovery to normal levels by 45 min was observed. Multimeric assay demonstrated a selective loss of high molecular weight multimers (HMWM) with subsequent replacement. At low doses, in non-human primates (chimpanzees), identical changes to those seen in the dog were observed and this was associated with an equivalent loss of ristocetin co-factor activity (vWF:RCoF). At high dose a reversal of the wWF response occurred with levels increasing to twice that of baseline values by 2 min and multimeric analysis demonstrated the presence of abnormally large multimers and increased vWF:RCoF specific activity, suggesting that the response at each dosage reflected a net balance of consumption over release. This was supported by in vitro simulation where increasing thrombin generation was associated with a selective loss of HMWM without replacement. In both species, an immediate fall in platelet count occurred and this was directly correlated with the amount of thrombin generated. Full recovery occurred within 45 min and isotopic labelling studies demonstrated that platelet sequestration rather than consumption was occurring. These studies demonstrate that thrombin generation in vivo is associated with a selective loss of the multimeric forms of vWF known to interact with platelets and this may provide an in vivo model to characterize the physiology/pathophysiology of this primary event in haemostasis.

Animals↗
PubMed1991

Alpha 2-macroglobulin binds and inhibits activated protein C.

In previous studies using a nonhuman primate model of Protein C (PC) activation in vivo, immunoblotting showed substantial amounts of activated PC (APC) in a high molecular weight complex with what was presumed to be a previously unrecognized APC binding protein. This APC complex can also be formed in citrated plasma in vitro. It is of low electrophoretic mobility, sodium dodecyl sulfate (SDS) stable, with an apparent Mr of 320 Kd. Its purification from human plasma was accomplished using barium citrate adsorption, sequential polyethylene glycol (PEG) precipitations, diethylaminoethyl sepharose chromatography, AcA-34 gel filtration, and zinc-chelate affinity chromatography. This was monitored by subjecting the fractions to nondenaturing polyacrylamide gel electrophoresis (PAGE), transfer to polyvinylidene-difluoride membranes, and probing with 125I-labeled human APC. The purified APC-binding protein was homogeneous by SDS-PAGE with an Mr of 275 Kd. Its identity as alpha 2-macroglobulin (alpha 2M) was demonstrated immunochemically. Complex formation between alpha 2M and APC was found to be almost completely inhibited by EDTA, but to a lesser extent by citrate. Complex formation could also be prevented by active site inhibition with D-Phenylalanyl-L-Prolyl-L-Arginine-Chloromethyl Ketone (PPACK) or pretreatment of alpha 2M with methylamine. Incubation of APC (33 nmol/L) with alpha 2M (1 mumol/L) resulted in time-dependent inhibition of APC anticoagulant activity when measured using an activated partial thromboplastin time based APC assay. These data show that alpha 2M binds and inhibits APC in vitro and the interaction is both metal-ion and active-site dependent, requiring functionally intact alpha 2M. As the complexes formed in vitro comigrate electrophoretically with those observed in vivo after PC activation, it is suggested that alpha 2M is a physiologically relevant inhibitor involved in the processing of APC in vivo.

Amino Acid Chloromethyl Ketones↗