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L Poller

Publications and source records attributed to L Poller.

At least 109 records · Page 6Linked to original sources
PubMed1983

Lipid class composition and heparin sensitivity in the activated partial thromboplastin time.

In an APTT reagent, prepared from purified lipids, the role of phosphatidyl serine (PS) in determining the sensitivity of the APTT test system to measurement of the effect of heparin in plasma has been evaluated. As the concentration of PS decreases sensitivity to heparin increases but procoagulant activity decreases. Dilution of the test liposome over a wide range (1 g/l to 30 mg/l) had a minimal effect on the clotting time. At levels below 30 mg/l, however, the amount of total lipid appeared to be rate limiting; a loss of procoagulant activity being paralleled by an increase in heparin sensitivity. Phosphatidyl inositol (PI) was not a satisfactory substitute for PS in the APTT method studied. The degree of unsaturation of test liposomes appeared to have no effect on either procoagulant activity or sensitivity to heparin at the lipid concentration employed. In the light of these findings, a more critical appraisal of the phospholipid components of APTT reagents should facilitate the development of more reliable reagents for heparin control. A further benefit of this type of approach should be a reduction in the acknowledged wide variations in sensitivity to heparin which exist between available APTT reagents.

Blood Coagulation Tests↗
PubMed1982

The procoagulant activity of partial thromboplastin extracts: the role of phosphatidyl serine.

The role of phosphatidyl serine (PS) in the procoagulant activity of the APTT test has been studied further, using extracts of improved purity derived from a combination of high performance liquid chromatography and thin layer chromatography. The central role of PS in the APTT has been confirmed but the anticoagulant effect described in our previous report has been localised to contamination with phosphatidyl inositol (PI). A comparatively weak procoagulant activity was detected in purified PI- and lyso PS-containing liposomes and the former had an inhibitory action in mixtures diluted to less than 1 microgram/litre. This was enhanced by the presence of PS in combination experiments. Some correlation was noted between the degree of unsaturation of test liposomes and their procoagulant activity. The observations suggest that PS has a precise and unique role in the procoagulant activity expressed in this test system. PS possesses a strong negative charge and has two fatty acid groups. Other negatively charged phospholipids in this test system were less active. It appears, therefore, that the packing of PS into the lipid bilayer, which depends upon the length and degree of unsaturation of its fatty acid groups, is of considerable importance in establishing the surface topography essential for optimal procoagulant activity. Knowledge of the role played by various phospholipids in the procoagulant activity of the APTT reagent should enable improved standardisation and quality control in the future.

Blood Coagulation↗
PubMed1982

An evaluation of APTT monitoring of low-dose heparin dosage in hip surgery.

The activated partial thromboplastin time has been used to monitor the effects of low-dose subcutaneous heparin in two groups of patients undergoing hip surgery. The study was performed to determine the degree of anticoagulation required to protect these high-risk patients from post-operative deep vein thrombosis. The patients were randomised to receive a fixed regimen of subcutaneous calcium heparin (5,000 units eight-hourly) or a dose of calcium heparin monitored by maintaining the standardised APTT at 50 secs. In the adjusted group the APTT achieved the target figure in 46% of observations compared to 27% in the fixed group (p less than 0.005). Nine patients showed positive 125I-fibrinogen scans and in all, the APTT was below the target value the day before the scan became positive. In contrast, in six of the nine thrombotic patients heparin was detected by antifactor Xa clotting assay. The APTT, therefore, appears to give a better guide to the antithrombotic effect of heparin than the antifactor Xa clotting assay. These preliminary observations suggest that prolonging the standardised APTT method to just above 50 secs improves prophylaxis in high-risk cases. Furthermore, an increased dose of heparin is required than is proved during the conventional low-dose regime of 5,000 units tds. With regular control using the standardised APTT, increasing the dose to the target value does not increase post-operative haemorrhage. Further studies with larger numbers of patients are required in order to show a significant reduction in the incidence of post-operative deep vein thrombosis in hip surgery patients receiving low-dose adjusted heparin.

Adult↗
PubMed1982

Dosage and control of oral anticoagulants: an international collaborative survey.

An international survey of oral anticoagulant dosage has been carried out comparing the mean dosage prescribed in hospitals in 23 countries. In addition, participants using the Quick prothrombin time test were asked to assess the adequacy of dosage of a lyophilized test plasma which was mid-therapeutic using the British Comparative Thromboplastin (BCT). The overall mean dosage proved similar for the groups of laboratories using the Quick test and human brain thromboplastin and Thrombotest although wide differences existed between individual centres. The survey indicated that these discrepancies were due partly to the adoption of different intensities of anticoagulation. In addition, local differences in patients' response to anticoagulants were apparent, e.g. North American centres prescribed a higher mean dose with a more intense therapeutic range than Europeans. Hong Kong physicians appear to prescribe a much lower dose than the rest of the world although the intensity of their treatment is comparable, whereas South African hospitals give moderate doses of warfarin despite a conservative therapeutic range. Such geographical variation in response would invalidate standardization of anticoagulant treatment based on the mean dosage approach.

Administration, Oral↗
PubMed1981

An evaluation of chromogenic substrates in the control of oral anticoagulant therapy.

A comparison has been made between the prothrombin time test using British Comparative Thromboplastin (BCT) and four modified amidolytic assays in the assessment of laboratory control of oral anticoagulant administration in short-term and long-term patients. The results were also correlated with the APTT and specific assays for factors VII and X based on established coagulation techniques. The chromogenic substrate assays did not give as close agreement with the BCT as the clotting assays for factors VII and X. A combination of the amidolytic factor II and X results did not improve the correlation. Agreement with the BCT was better in long-term patients with the substrates but there was no obvious advantage between the factor II and X amidolytic methods in this group. The development of a specific amidolytic assay for factor VII should be considered based on the evidence of this study although its reliability for oral anticoagulant control would need to be validated by clinical trial. In the interim, it may be anticipated that thromboplastins showing less sensitivity than BCT to factor VII would give a better correlation with the amidolytic assays.

Acenocoumarol↗
PubMed1981

An assessment of an amidolytic assay for factor VII in the laboratory control of oral anticoagulants.

A comparison has been made between the prothrombin time test using British Comparative Thromboplastin (BCT) and a chromogenic substrate assay for factor VII in the assessment of laboratory control of oral anticoagulants in short-term and long-term patients. Opportunity was also taken to compare the findings with parallel results obtained with the venous Thrombotest technique and a specific clotting assay for factor VII. There was good agreement between the amidolytic factor VII assay, using a method modified from Seligsohn et al (1978) with the Quick test using BCT and Thrombotest in 60 long-term patients. Tests in 53 patients within the first 3 weeks of starting oral anticoagulant administration gave less satisfactory agreement between the above amidolytic method and the conventional tests. In contrast, there was a good correlation between the two conventional tests in both groups and also between the clotting and amidolytic factor VII method. Although the results are an improvement on previous, less satisfactory correlations between the BCT prothrombin time method and amidolytic assays for factor II and X, the present study indicates the limitations of a specific clotting assay versus a broad spectrum extrinsic clotting test in oral anticoagulant control. While not warranting the routine use of the chromogenic assay for factor VII in place of the prothrombin time using BCT, the factor VII amidolytic assay offers a limited but dependable guide to dosage in long-term patients. The complexity of the technique in its present form militates against its adoption for routine anticoagulant control in hospital laboratories.

Acenocoumarol↗
PubMed1981

A study of the procoagulant properties of amniotic fluid and their correlation with the lecithin/sphingomyelin ratio.

The procoagulant properties of amniotic fluid have been studied in samples taken throughout pregnancy and the results correlated with the lecithin/sphingomyelin ratio: acceleration effects on the prothrombin time. Russell's viper venom test, activated partial thromboplastin time and specific factor VII and X assays and contact acceleration. Although amniotic fluid is shown to function as a complete thromboplastin and to activate factor X directly, none of these tests of procoagulant activity of amniotic fluid is a reliable index of fetal lung maturity.

Amniotic Fluid↗
PubMed1981

Prostacyclin-like, and kallikrein activity of amniotic fluid in pre-eclampsia.

Amniotic fluid from patients with pre-eclampsia was compared with samples obtained from normotensive controls with respect to the inhibiting effect on platelet aggregation (PGI2-like activity) and activating effect on the plasma kallikrein assay and Russell's viper venom test. After 39 weeks gestation, amniotic fluid from pre-eclamptic patients showed significantly less PGI2-like activity ( p less than 0.01) and significantly lower kallikrein levels (p less than 0.01) than that from normotensive controls. The study suggests that the biosynthesis and release of PGI2-like activity and kallikrein may be impaired in pre-eclampsia. In view of the association of pre-eclampsia with intravascular clotting, the highly significant reduction of PGI2-like activity seems important and appears to warrant a clinical trial of prostacyclin administration in this disorder.

Amniotic Fluid↗
PubMed1980

Heparin and partial thromboplastin time: an international survey.

The reliability of routine partial thromboplastin time (PTT) methods in the measurement of the anticoagulant effect of heparin has been assessed in a study involving over 300 hospitals in the U.S. and overseas. Commercial PTT methods were relatively insensitive to heparin, added in vitro, compared with the standardized PTT method tested by the same laboratories. Non-commercial, locally-prepared reagents compared well with the standardized method particularly in the detection of a low concentration of heparin. The value of a sensitive reference preparation for the calibration of routine PTT reagents used in heparin control is demonstrated.

Blood Coagulation↗
PubMed1980

The British Comparative Thromboplastin: the relationship between lipid class composition and procoagulant activity.

Twenty-eight consecutive batches of the reference reagent British Comparative Thromboplastin (BCT) were produced in the National (UK) Reference Laboratory for Anticoagulant Reagents and Control (NRLARC) between 1969 and 1977. The relationship between procoagulant activity and lipid class composition in these batches at various stages of age deterioration on storage has been studied by a modification of the method of high pressure chromatography which allows better definition of the individual lipids. The free fatty acid concentration rose markedly while cconcentrations of phosphatidyl choline, phosphatidyl ethanolamine and phosphatidyl serine were reduced. An oxidative process is suggested and supported by the increase in malonaldehyde levels. The method of production of the BCT involves maceration of human brain which causes the breakdown of cell membranes and the release of many potentially oxidative materials from subcellular particles. The loss of procoagulant activity of BCT on storage may be due to the loss of phospholipid or to the increase of inhibitory degradation products, i.e. free fatty acid and malonaldehyde. The examination of the lipid class composition of tissue thromboplastin extracts appears useful, therefore, not only in determining the phospholipids necessary for procoagulant activity, but also in monitoring the deterioration of tissue thromboplastins on storage.

Humans↗
PubMed1980

Fibrinogen determination in a series of proficiency studies.

Fibrinogen estimations were performed in four quality control proficiency studies conducted by the National (UK) Reference Laboratory for Anticoagulant Reagents and Control for over five hundred hospitals in the UK and overseas during 1976--1978, to evaluate the various techniques in current practice. More than 30 different estimation techniques were employed by participants and these could be classified into eight groups. The success in detecting a fibrinogen level below the normal range ('sensitivity') and reliability in providing a normal result for a value within the normal range ('specificity') have been determined. No method failed in both aspects. The tyrosine, clot weight, immunological and Clauss technique appeared reasonably satisfactory. The best results were obtained with the Clauss technique although the difference between this and the other quantitative techniques did not achieve statistical significance. Some were less dependable, notably the turbidity techniques and the thrombin time. Although no technique appeared to be superior to others from the standpoint of precision, turbidity techniques appeared to be the least precise showing the largest co-efficient of variation.

Fibrinogen↗
PubMed1980

A double-blind cross-over study of piperazine oestrone sulphate and placebo with coagulation studies.

A double-blind trial of piperazine oestrone sulphate was performed over a period of 14 months on 55 menopausal women complaining of depressiona and hot flushes. Depression was not affected but the hot flushes were significantly lessened by the oestrogen treatment. After three months of piperazine oestrone sulphate there were no significant accelerations of prothrombin time or increases in factors VII or X but, after six months, there was an acceleration in the prothrombin time. After 14 months those who received piperazine oestrone sulphate for the first six months showed a significant increase in alpha 1-antitrypsin and factor VIIR:AG. Oestrone piperazine sulphate appears to produce less marked changes in coagulation than oestrogen-containing oral contraceptives or conjugated equine oestrogens.

Blood Coagulation↗
PubMed1980

Standardization of the APTT test. Current status.

The partial thromboplastin time (PTT) which is used as an overall measure of the intrinsic clotting system, is the commonest coagulation test employed in routine laboratories apart from the prothrombin time. The main functions of the test are: - 1. to screen intrinsic coagulation defects; 2. to control heparin administration; 3. in the control of oral anticoagulant treatment. Many different preparations of phospholipid of human, animal and vegetable origin are used as PTT reagents. In addition, different activators, incubation times, concentrations of calcium chloride and test dilutions of plasma and phospholipid are recommended for routine laboratory use. The need to standardise both reagents and technique has been emphasised in many reports. To meet the need for a reference preparation for the PTT test, a large batch of phospholipid material of human brain origin, designated 71/25, was prepared in the National (UK) Reference Laboratory in lyophilised form in 1971 and proposed as a provisional international reference material. This primary master preparation has been used to calibrate subsequent batches of secondary reference preparations distributed to hospitals in the UK and overseas. Results of a number of collaborative studies have demonstrated the greater reliability of the standardised PTT extract compared with commercial extracts used at the same centres in the three aspects of PTT testing. The conclusion to be drawn from these extensive studies of the laboratory and clinical application of the provisional international reference preparation (71/25) is that we may now be in a position to define an acceptable international standard for the APTT.

Administration, Oral↗