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Biomedical subjects

S Kitchen

Publications and source records attributed to S Kitchen.

At least 55 records · Page 3Linked to original sources
PubMed1997

Potentially clinically important inaccuracies in testing for the lupus anticoagulant: an analysis of results from three surveys of the UK National External Quality Assessment Scheme (NEQAS) for Blood Coagulation.

The identification of the presence of antiphospholipid in plasma is recognised to be of diagnostic and prognostic importance in subjects with thrombotic disease, recurrent miscarriage or collagen vascular disorders. A number of coagulation assays are currently employed for the detection of lupus anticoagulant (LA), many of which are influenced by reagent dependent and methodological variables. In the present study lyophilised plasma samples from three subjects with "strong", "weak" and "absent" LA were tested in 220 centres. The most commonly used tests for LA were Activated Partial Thromboplastin Time (APTT), Dilute Russell Viper Venom Time (DRVVT) and Kaolin CLotting Time (KCT). Median DRVVT ratios were 1.75, 1.17 and 1.10 for the three samples. The presence of a strong LA was not detected by 4% of laboratories. The correct diagnosis was made by 94% of users of DRVVT and 85% of users of KCT. A weak LA was not detected by over half of centres. Correction was observed on addition of plasma and also in platelet neutralisation. The correct diagnosis was made by 37% of users of DRVVT and 27% of users of KCT. Lupus Anticoagulant was falsely considered to be present in a Factor IX deficient plasma by approximately one quarter of laboratories. Amongst users of DRVVT and KCT absence of LA in this sample was correctly reported by 73% and 69% of centres respectively. The accuracy of testing for LA in the present study is suboptimal and this is likely to have important clinical consequences. There is clearly a need for greater conformity in the selection and performance of LA tests to facilitate accurate diagnosis of this important group of disorders.

Antiphospholipid Syndrome↗
PubMed1996

Acute myelofibrosis terminating in acute lymphoblastic leukemia: case report and review of the literature.

Acute myelofibrosis (AMF), as defined by an acute panmyelopathy associated with marked megakaryocytic hyperplasia and marrow fibrosis, appears to be a stem cell disorder. Even though it is most difficult to distinguish from various myeloproliferative and myelodysplastic disorders as well as acute myelogenous leukemia, it has rarely been reported to terminate as acute lymphoblastic leukemia (ALL). Only five cases have been reported in the literature; two from the pediatric literature and only three from the adult literature. Of the three adult cases, two were defined by light microscopy alone. Among the cases with follow-up (3/5), all died within 2 weeks to 2 months of diagnosis. We report an additional case in an adult; the ALL was defined by morphology, flow cytometric immunophenotyping, and cytogenetic analysis. The interval from diagnosis of AMF to ALL was 3 months. Our patient was treated with standard therapy for ALL, was in complete remission at last follow-up (3 months off maintenance therapy), and represents the only reported case who attained a complete remission. There are too few cases to determine the prognostic significance of termination of AMF in an acute leukemia of lymphoid origin vs. myeloid origin.

Adult↗
PubMed1996

Differential tropism of HIV-1 isolates for distinct thymocyte subsets in vitro.

OBJECTIVE: Understanding the interaction between HIV and developing thymocytes is crucial in determining how HIV infection perturbs the immune system. We determined which thymocyte subsets can harbor and express HIV. DESIGN: HIV expression in mature and immature thymocytes obtained from surgical specimens from non-infected children was determined after in vitro infection with the syncytium-inducing, cytopathic NL4-3 and the non-syncytium-inducing, relatively noncytopathic JR-CSF isolates. METHODS: Intracellular staining for the HIV p24gag antigen was combined with cell surface phenotyping to determine thymocyte subsets expressing HIV. Infection was quantitated by polymerase chain reaction on sorted subsets. RESULTS: NL4-3 replicated faster and to higher titers and caused a more severe decrease of all CD4-bearing thymocytes than did JR-CSF. In addition, both immature CD1+ and mature CD1-thymocytes expressed NL4-3, whereas only mature CD1-cells expressed JR-CSF. The tropism of NL4-3 for these immature cells suggests a mechanism for a more profound impact on T-cell maturation than that seen with JR-CSF. We also found that thymocytes lacking cell surface CD4 (CD4-CD8- and CD4-CD8+ subsets) expressed virus with either isolate late in infection, when viral levels were high. The CD4-CD8- cells expressing HIV were mature CD3bright T-cell receptor (TCR) alpha/beta bright cells. CONCLUSIONS: These results show that NL4-3 can be expressed by thymocytes at immature and mature stages of differentiation and cause severe loss of CD4+ cells. Thus, tropism of a virus for immature cells can affect the capability of the thymus to produce new T lymphocytes leading to a greater impact on development and functions of the immune system. It is proposed that this in vitro model can be used to study pathogenic mechanisms in the thymus.

Antibodies, Monoclonal↗
PubMed1996

Wide variability in the sensitivity of APTT reagents for monitoring of heparin dosage.

AIM: To assess the sensitivity of activated partial thromboplastin time (APTT) reagents for monitoring heparin dosage using data from the UK National External Quality Assessment Scheme (NEQAS) for blood coagulation. METHODS: Data were reviewed from four surveys using samples prepared by addition of heparin to normal plasma in vitro and from two surveys in which samples were prepared using plasma from patients receiving heparin therapy (ex vivo samples). RESULTS: For both in vitro and ex vivo samples, notable differences between APTT reagents with respect to heparin sensitivity were noted. This indicates that a uniform therapeutic range of 1.5-2.5 calculated by the APTT ratio may not be appropriate for all reagents. Reagent sensitivity in ex vivo samples was substantially different to that in in vitro samples. CONCLUSIONS: The results of this large series of laboratories clearly indicate that reagent specific therapeutic ranges may be necessary, and that samples prepared by the addition of heparin to normal plasma in vitro can be misleading and should not be used.

Acute Disease↗
PubMed1996

The therapeutic range for heparin therapy: relationship between six activated partial thromboplastin time reagents and two heparin assays.

The activated partial thromboplastin time (APTT) is the most commonly used test for laboratory monitoring of unfractionated heparin therapy. Since there are differences between APTT reagents in respect of responsiveness to heparin the widely used therapeutic range of 1.5-2.5 (APTT ratios) may not be appropriate for all reagents. The aim of this study was to assess the relationship between 6 different APTT reagents using a manual technique, 2 of these reagents used in combination with a coagulometer, a heparin assay by protamine titration and a chromogenic anti-Xa assay. Samples from 42 patients treated with unfractionated heparin for thromboembolic disease were studied, 12 of whom were receiving warfarin therapy with International Normalised Ratios (INR) of > 1.3. For normal subjects, APTT results were highly dependent on the method used and statistically significant differences were noted. The ratio of patient to mean normal APTT was calculated for each APTT method. When 30 samples from heparinised patients (with INRs of < 1.3) were analysed manually, the APTT ranges equivalent to 0.2-0.4 u/ml heparin by protamine titration (by regression analysis) were 1.6-1.9 for Boehringer reagent (the least responsive) up to 2.2-2.9 for Instrumentation Laboratory reagent (the most responsive). The concentration of heparin associated on average with APTT ratios of 1.5-2.5 varied approximately twofold to threefold between reagents.

Adult↗
PubMed1996

Two recombinant tissue factor reagents compared to conventional thromboplastins for determination of international normalised ratio: a thirty-three-laboratory collaborative study. The Steering Committee of the UK National External Quality Assessment Scheme for Blood Coagulation.

Recent advances in recombinant technology have led to the development of prothrombin time (PT) reagents containing recombinant tissue factor which has been lipidated to allow expression of procoagulant activity. In this study we have compared International Normalised Ratios (INRs) determined using two such reagents and conventional thromboplastins in widespread use in the UK. Lyophilised plasma samples from eight different warfarinised patients were distributed to 33 laboratories in the UK. Each participant determined prothrombin times on 20 local fresh normal plasmas (used to derive mean normal PT and calculate INR) and the eight lyophilised samples, using manual technique and the following thromboplastins; Recombiplastin (Ortho Diagnostics Ltd); Innovin (Baxter Diagnostics Ltd); the conventional thromboplastin in local use. For eight plasmas the mean INRs determined with different reagents were as follows: Innovin (33 laboratories) - 3.4; Manchester Reagent (MR = 8 laboratories) - 3.4; Recombiplastin (33 laboratories) - 3.7; Instrumentation Laboratory (IL = 13 laboratories) - 4.4. Mean INR results with Recombiplastin were on average 7% greater than those obtained with Innovin, 8% greater than results with MR and 18% less than INRs with IL thromboplastin. There was no significant difference between results obtained with Innovin and MR. In contrast INRs obtained with IL were markedly (mean 28%) greater than results obtained with Innovin. This study employed lyophilised plasma and it is possible that some of the relationships described are influenced by this. However, the lyophilisation process employed did not influence the relationship between INRs of warfarinised plasmas obtained by the four main reagents described, indicating that the results are relevant to routine clinical practice. In conclusion, our data show some important differences are present between INRs determined using Recombiplastin, Innovin and two conventional thromboplastins.

Humans↗
PubMed1995

Human immunodeficiency virus 1 envelope proteins induce interleukin 1, tumor necrosis factor alpha, and nitric oxide in glial cultures derived from fetal, neonatal, and adult human brain.

Although microglia are the only cells found to be productively infected in the central nervous system of acquired immunodeficiency disease syndrome (AIDS) patients, there is extensive white and gray matter disease nonetheless. This neuropathogenesis is believed to be due to indirect mechanisms other than infection with human immunodeficiency virus 1 (HIV-1). Cytokines and toxic small molecules have been implicated in the clinical and histopathological findings in CNS AIDS. Previously, we have demonstrated in rodent glial cultures the presence of biologically active epitopes of gp120 and gp41 that are capable of inducing interleukin 1 and tumor necrosis factor alpha. In this study, we map the HIV-1 envelope epitopes that induce nitric oxide, inducible nitric oxide synthase, interleukin 1, and tumor necrosis factor alpha in human glial cultures. Epitopes in the carboxy terminus of gp120 and the amino terminus of gp41 induce these proinflammatory entities. In addition, we compare HIV-1 infection and pathology in glial cells derived from human brain taken at different states of maturation (fetal, neonatal, and adult brain) in an effort to address some of the clinical and histological differences seen in vivo. This study demonstrates that, in the absence of virus infection and even in the absence of distinct viral tropism, human glia respond like rodent glia to non-CD4-binding epitopes of gp120/gp41 with cytokine and nitric oxide production. Differences among fetal, neonatal, and adult glial cells' infectivity and cytokine production indicate that, in addition to functional differences of glia at different stages of development, cofactors in vitro and in vivo may also be critical in facilitating the biological responses of these cells to HIV-1.

Adolescent↗
PubMed1994

Thromboplastin related differences in the determination of international normalised ratio: a cause for concern? Steering Committee of the UK National External Quality Assessment Scheme in Blood Coagulation.

When the International Normalised Ratio (INR) is used for control of oral anticoagulant therapy the same result should be obtained irrespective of the laboratory reagent used. However, in the UK National External Quality Assessment Scheme (NEQAS) for Blood Coagulation INRs determined using different reagents have been significantly different. For 18 NEQAS samples Manchester Reagent (MR) was associated with significantly lower INRs than those obtained using Diagen Activated (DA, p = 0.0004) or Instrumentation Laboratory PT-Fib HS (IL, p = 0.0001). Mean INRs for this group were 3.15, 3.61, and 3.65 for MR, DA, and IL respectively. For 61 fresh samples from warfarinised patients with INRs of greater than 3.0 the relationship between thromboplastins in respect of INR was similar to that observed for NEQAS data. Thus INRs obtained with MR were significantly lower than with DA or IL (p < 0.0001). Mean INRs for this group were 4.01, 4.40, and 4.59 for MR, DA, and IL respectively. We conclude that the differences between INRs measured with the thromboplastins studied here are sufficiently great to influence patient management through warfarin dosage schedules, particularly in the upper therapeutic range of INR. There is clearly a need to address the issues responsible for the observed discrepancies.

Animals↗
PubMed1993

Somatostatin analogue (octreotide) inhibits bile duct epithelial cell proliferation and fibrosis after extrahepatic biliary obstruction.

Extrahepatic biliary obstruction leads to bile duct epithelial cell proliferation. Somatostatin and its analogue, octreotide, have been shown to inhibit DNA synthesis and proliferation in hepatocytes. We investigated the effect of octreotide on the biliary epithelial cell proliferative responses to biliary obstruction. Male Sprague-Dawley rats underwent common bile duct ligation and subcutaneous injection of either saline or octreotide (6 micrograms/kg) twice daily for 7 days. Morphometric analysis of hepatocytes, bile duct epithelial cells, and periportal connective tissue was performed by computerized point counting. Hepatocyte volume was preserved with octreotide treatment, which also significantly decreased bile duct proliferation and periportal extracellular matrix deposition in response to biliary obstruction compared with saline treated, duct-ligated animals. These results indicate that octreotide prevents the morphological changes that accompany extrahepatic biliary obstruction.

Animals↗
PubMed1992

A comparison of methods for the measurement of activated factor VII.

A number of different methods are available for the measurement of factor VIIa. Almost all of these employ ratios of two different measurements of factor VII. In order to determine which is the most sensitive to activated factor VII we have compared currently available methods in the following groups: two patients with haemophilia A following treatment with activated recombinant factor VII (rVIIa); 6 normal plasmas during cold promoted activation of factor VII; normal individuals (n = 23); and patients with unequivocal disseminated intravascular coagulation (DIC, n = 19). Factor VII was measured in an amidolytic assay (VII:Amid) and an antigen assay (VII:Ag). Clotting activity was measured using rabbit (VII:C Rab), human (VII:C Hum) and bovine (VII:C Bov) thromboplastin. Of the clotting assays the most sensitive to the presence of factor VIIa was that which utilised bovine thromboplastin. Amidolytic and immunological measurements were unaffected by the activity state of factor VII. The ratios VII:C Rab/VII:Ag and VII:C Rab/VII:Amid were insensitive to activated factor VII. The ratios most sensitive to the presence of factor VIIa were VII:C Bov/VII:Amid and VII:C Bov/VII:Ag. The ratios VII:C Bov/VII:C Rab and VII:C Bov/VII:C Hum are less sensitive but have the advantage for epidemiological studies of narrower reference ranges.

Adult↗
PubMed1991

Potential thrombogenicity of heat-treated prothrombin complex concentrates in Haemophilia B.

We have studied the potential thrombogenicity of two different heat-treated prothrombin complex concentrates (PCC) in patients with Haemophilia B. Seven patients were studied on nine separate occasions. Four of the patients had chronic hepatitis C (HCV) associated liver disease and three were HIV-antibody positive. The PCCs were Profilnine (Alpha Therapeutics, Thetford, UK) and 9A (Bio-Products Laboratory, Elstree, UK) and the dose administered ranged from 35 to 60 U/kg. Blood samples were taken on ten separate occasions; twice before the infusion and at 15, 40, 60, 75 and 120 min and 4, 8 and 24 h after the infusion of PCC. Investigations included prothrombin time, kaolin cephalin clotting time, thrombin time, fibrin(ogen) degradation products, factor VIII, factor IX, antithrombin III and fibrinopeptide A (FPA). Fibrinopeptide A rises were seen following two of six infusions of 9A and one of three infusions of Profilnine. On all three occasions the rise in FPA was transient, returning to baseline levels within 120 min. Plasma beta-thromboglobulin (BTG) was assayed in three patients and in one patient, the rise in FPA was followed by an increase in BTG. No other changes were observed and there were no clinical features of disseminated intravascular coagulation. Our results indicate that even with normal clinical doses of PCC, intravascular thrombin generation can occur in patients with Haemophilia B. However, this effect is inconsistent both with respect to PCC batch and patient, but may occur in the absence of HIV infection and HCV liver disease.

Blood Coagulation↗
PubMed1991

Activation of coagulation in diabetes mellitus in relation to the presence of vascular complications.

To examine the relationship between diabetic vascular disease and haemostasis, a set of sensitive assays has been used to assess in vivo activation of coagulation in 62 diabetic patients (41 Type 1 and 21 Type 2), aged 19-68 years, who had been screened for the presence of complications. Fibrinopeptide A, an index of thrombin activity, was significantly increased in diabetic patients compared with control subjects (p less than 0.05), in both plasma (with complications mean 8.04 +/- 11.87 (+/- SD); without complications 7.21 +/- 10.13; control subjects 2.11 +/- 1.40 micrograms l-1) and urine (with complications mean 1.48 +/- 0.74; without complications 1.35 +/- 0.62; control subjects 0.98 +/- 0.39 micrograms l-1). Activated factor VII (VIIa ratio 1.21 +/- 0.39; 1.13 +/- 0.23; 1.01 +/- 0.11) and fibrinogen (3.15 +/- 0.59; 3.11 +/- 0.69; 2.70 +/- 0.57 g l-1) were also elevated in diabetic patients with and without complications (VIIa p less than 0.05, fibrinogen p less than 0.01). The only difference between Type 1 and Type 2 patients was in fibrin degradation products (Type 1 0.28 +/- 0.18; Type 2 0.40 +/- 0.18 mg l-1, p less than 0.01). Plasma levels of fibrin degradation products were elevated in diabetic patients (p less than 0.05 vs control subjects), and correlated with age (r = 0.44, p less than 0.01) but were unrelated to the presence of complications. There were no significant differences in any coagulation variables between diabetic patients with and without complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Inhibition of activated protein C and its cofactor protein S by antiphospholipid antibodies.

We have investigated the effects of purified IgG fractions from plasma containing the lupus anticoagulant (LAC) and/or IgG anticardiolipin antibody (ACA) on the degradation of factor Va by an activated protein C-protein S complex. Plasma samples from 10 patients were studied. LAC was detected by a Russell's Viper venom technique. ACA was determined by ELISA. IgG fractions were obtained from each plasma sample by protein A-Sepharose fractionation. This fraction was shown to exhibit ACA/LAC activity. Using purified activated protein C (APC), protein S and phosphatidylserine/phosphatidylcholine, factor Va degradation was assessed in the presence and absence of IgG fractions from LAC/ACA containing plasmas. After 2 min incubation the mean factor Va degradation by APC and protein S in the presence of IgG LAC/ACA fractions was 14% compared with 52% with normal IgG. A similar effect was seen when phospholipid was substituted by washed freeze-thawed platelets. Experiments employing varying concentrations of protein S and phospholipid revealed marked differences in respect of the inhibitory specificity of the different antiphospholipid antibodies. These results indicate that antiphospholipid antibodies have an inhibitory effect on the activated protein C/protein S complex and provide some explanation for a relationship between antiphospholipid antibodies and thrombosis.

Autoantibodies↗
PubMed1989

Plasma D-dimer levels and their relationship to serum fibrinogen/fibrin degradation products in hypercoagulable states.

Plasma D-dimer was measured and compared with serum fibrinogen/fibrin degradation product levels (FDPs) in patients with disseminated intravascular coagulation (DIC) and other conditions associated with a hypercoagulable state. D-dimer (N less than 200 ng/ml) was elevated in all 43 patients with DIC, in 48 of 59 patients with liver disease, in 22 of 27 patients with acute leukaemia at presentation, in 17 of 23 patients with malignant disease, in 29 of 39 women in the third trimester of a complicated pregnancy, in 17 of 18 patients with deep venous thrombosis and in only four of 27 patients with acute myocardial infarction. There was a significant correlation between plasma D-dimer and serum FDP levels (P less than 0.01) as follows; DIC: r = 0.58, liver disease: r = 0.57, acute leukaemia: r = 0.84, malignancy: r = 0.87. The frequent elevation of D-dimer observed in liver disease, acute leukaemia, malignancy and complicated pregnancy indicates that a hypercoagulable state is a common occurrence in these conditions although in liver disease elevated levels resulting from a failure of normal clearance mechanisms cannot be excluded. The close relationship between D-dimer and FDP levels suggests that serum FDPs predominantly arise from the interaction of plasmin with crosslinked fibrin rather than with fibrinogen in the conditions in which these were compared.

Blood Coagulation Disorders↗
PubMed1988

A method for the determination of activated factor VII using bovine and rabbit brain thromboplastins: demonstration of increased levels in disseminated intravascular coagulation.

Factor VII levels as measured in one stage clotting assays are dependent on the degree of activation of factor VII and on the type of thromboplastin used. Bovine thromboplastin (BT) is known to be more sensitive to factor VIIa than human brain thromboplastin and the different sensitivities of these reagents to VIIa have formed the basis of a method for determining VIIa in plasma (16). Since human thromboplastin is no longer widely available, we have re-evaluated this method using bovine and two rabbit thromboplastins (Manchester Reagent, RT MR and Diagen activated, RT Diagen). Activated factor VII was generated in normal plasma by cold activation for 24 hours. During this period, factor VII assays using bovine thromboplastin increased markedly with time whereas the assays using rabbit thromboplastins showed considerably less change. The ratio of factor VII (bovine thromboplastin)/factor VII (rabbit thromboplastin) is a sensitive index of activated factor VII in plasma. The mean ratio in normal plasmas (using BT and RT MR) was found to be 1.02 (+/- s.d., range 0.80-1.24). The ratio was measured in 29 samples from patients with disseminated intravascular coagulation (D.I.C.) and was found to be increased in 24 (mean 1.71, range 0.93-3.38).

Adult↗