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Biomedical subjects

L Poller

Publications and source records attributed to L Poller.

At least 37 records · Page 2Linked to original sources
PubMed1989

Randomized study of adjusted versus fixed low dose heparin prophylaxis of deep vein thrombosis in hip surgery.

A randomized study of adjusted versus fixed low dose heparin prophylaxis has been conducted in 100 patients undergoing surgery for hip replacement or fractured neck of femur. The two types of patients were randomized independently into the adjusted and fixed dose regimens. Patients in the adjusted group were controlled by an activated partial thromboplastin time method particularly responsive to the anticoagulant effect of heparin. The aim was to maintain the peak value just above the upper limit of the normal range. Adjustment of dosage began 24 h after surgery in the replacement group and 24 h after admission in the fracture group. Significant improvement in protection against postoperative deep vein thrombosis, assessed by venography, was observed in the adjusted group undergoing hip replacement (P = 0.013) and overall in both groups (P = 0.017) compared with a conventional fixed dose subcutaneous regimen (calcium heparin 5000 units, 8-hourly). In most instances, adjustment resulted in increased heparin dosage but this was not associated with any evidence of excessive bleeding.

Adult↗
PubMed1989

Special report: a simple system for the derivation of International Normalized Ratios for the reporting of prothrombin time results with North American thromboplastin reagents.

The World Health Organization international scale of reporting prothrombin time results is based on the calibration of thromboplastins against an international reference preparation to derive an International Sensitivity Index (ISI). Once the ISI has been assigned to an individual thromboplastin reagent, the derivation of International Normalised Ratios (INRs) for reporting results depends on mathematic formulae requiring a special calculator or mathematic tables. This causes difficulties and errors. A simplified system for interpretation of INRs with the range of thromboplastins widely used in North America is therefore presented, which obviates the need for mathematic procedures for the derivation of INR equivalents. It should thus facilitate the application of the INR system and of safer therapeutic ranges.

Calibration↗
PubMed1989

Effect of international sensitivity index (ISI) of thromboplastins on precision of international normalised ratios (INR)

The contribution of the thromboplastin international sensitivity index (ISI) to the interlaboratory coefficient of variation (CV) of the international normalised ratio (INR) with individual reagents was assessed. In theory the precision of the INR should increase with lower ISI values. An empirical relation has been established between the ISI, the INR, and its CV for two rabbit thromboplastins used in sufficient numbers for analysis in the United Kingdom. This was based on the cumulative data from the United Kingdom National External Quality Assessment Scheme (NEQAS) surveys over two years beginning in 1986. The actual precision achieved in NEQAS for the two reagents depends on the ISI value of the thromboplastin and it agreed closely with the figure predicted by the empirical model. The findings show that the ISI value of a thromboplastin strongly influences the interlaboratory variability of the INR obtained with it. The CV of the INR approximates to the CV of the prothrombin ratio multiplied by the ISI. Manufacturers of thromboplastin should therefore be encouraged to produce reagents showing good precision of results reported as simple prothrombin ratios and a low ISI value to avoid impairment in precision when ratio results are transformed to INR.

Animals↗
PubMed1989

Effect of automation on prothrombin time test in NEQAS surveys.

The performance of coagulometers in the National Quality Assessment Scheme (NEQAS) surveys of the prothrombin time conducted between 1986 and 1987 was reviewed. There were sufficient data for analysis for eight types of coagulometer used with a single type of thromboplastin reagent and one instrument with an alternative reagent. The overall reliability efficacy of each instrument was evaluated by determining the orthogonal regression slope parameters for prothrombin time (PT) and international normalised ratios (INR) using the manual technique as the reference method. Seven of the eight types of coagulometer tended to overestimate the INR. A pattern frequently observed with coagulometers, and difficult to regulate, was a trend to underestimate INR below 3.0 and overestimate higher INR. Overestimation of INR values over 3.0 was particularly pronounced with three types of instrument (Fibrintimer, Lancer, KC4/10). The KC4/10 was used by a sufficient number of participants to permit analysis of the performance of individual instruments. Within instrument differences were similar to those produced by different types of coagulometers. Thromboplastin reagents affected the INR values obtained with coagulometers. The study indicates that each local reagent-instrument combination must be calibrated by the participant to obtain reliable INR values. The use of a general correction factor for a local PT system seems to be invalid owing to the considerable variation in performance of individual coagulometers. The two best guides to the choice of coagulometer may be the deviation from the manual result and precision estimated by the coefficient of variation of the INR.

Blood Coagulation Tests↗
PubMed1988

A simple nomogram for the derivation of international normalised ratios for the standardisation of prothrombin times.

The WHO international scale of reporting prothrombin time results is based on the calibration of local and commercial thromboplastin reagents used in the test against an international reference preparation to derive an International Sensitivity Index (ISI) for each batch of local reagent. This quantifies an individual reagent's responsiveness to the coumarin induced defect. Once the ISI has been assigned, the derivation of International Normalised Ratios (INR) for reporting results depends on the use of a scientific calculator by which the local ratio is raised to the power of the ISI of the local reagent or use of an alternative formula and logarithms. A system for interpretation of INR, without the need for calculations, is presented for the known range of thromboplastins between 1.0 and 3.0 ISI in nomogram form. This chart may facilitate the general application of the INR system.

Humans↗
PubMed1988

The reliability of international normalized ratios during short-term oral anticoagulant treatment.

The reliability of the international normalized ratios (INR) system in the induction phase of coumarin administration has been studied in 15 serial patients over the first 7-40 days of treatment (mean 13.1). The INR results obtained with a variety of thromboplastin reagents have been compared with those obtained with the WHO second primary IRP, BCT/253. A wide divergence of INR values was observed with the various thromboplastins on each day of testing. INR values cannot therefore be relied upon with some of these reagents in the early days of anticoagulant treatment. This probably arises from the difference in responses of the thromboplastins to depression of vitamin K-dependent clotting factors. Consistent deviations from the IRP suggested that additional error may be due to inaccurate calibration of their products by the manufacturers. When the slopes of the sensitivity of the individual reagents to clotting factors II, VII and X were compared, however, results overall more closely approximated to those of the IRP when the INR were substituted for simple prothrombin ratios.

Acenocoumarol↗
PubMed1988

Survey of prothrombin time in National External Quality Assessment Scheme exercises (1980-87).

National External Quality Assessment Scheme surveys on the prothrombin time test carried out in hospitals in the United Kingdom have been performed at regular intervals since 1972. Performance has been assessed by comparing observed variability between hospitals with that predicted by a statistical model. The model was based on results from 53 survey plasmas issued between 1980 and 1987. These showed a linear correlation between logarithms of mean and standard deviation of reported ratios. Precision improved until the human brain thromboplastin, Manchester Comparative Reagent, was withdrawn in January 1986. There then followed a pronounced overall deterioration which, by October 1987, had not corrected to the levels achieved by 1985. When the recent results from 1986-87 were analysed according to Quick test reagent only one reagent (ISI 1.1) showed an improvement in precision. Performance of the other Quick test reagents, all with higher ISI values, had not regained the standards of precision previously achieved by the human brain reagent.

Animals↗
PubMed1987

Fixed minidose warfarin: a new approach to prophylaxis against venous thrombosis after major surgery.

A prospective study was carried out to see whether a small fixed dose of warfarin (1 mg daily) given before operation (mean 20 days) would prevent deep vein thrombosis in patients having major gynaecological surgery. One hundred and four patients were randomised into three groups: fixed minidose warfarin; full dose oral anticoagulation; and no treatment (controls). There was a significantly lower incidence of deep vein thrombosis in the minidose warfarin and full dose anticoagulant treatment groups (9% (3/32) and 3% (1/35) respectively) than in the controls (30%; 11/37) but no significant difference between the two anticoagulant treatment groups. Prothrombin time and the activated partial thromboplastin time were normal on the day of surgery in the warfarin treatment group, whereas times were prolonged in the group given full dose anticoagulation. Mean haemoglobin concentrations fell in all three groups after operation but the fall was significantly less in the minidose warfarin treatment group than after full dose anticoagulation. The benefit from full dose oral anticoagulant prophylaxis, based on a preoperative international normalised ratio of 1.5-2.5 with rabbit brain Manchester reagent, was similar to the protection achieved in an oral anticoagulant treatment group controlled with human brain Manchester comparative reagent at a similar level of anticoagulation. The lack of disturbance of normal haemostasis at the time of operation together with a significant reduction in deep vein thrombosis may encourage surgeons to introduce minidose prophylaxis with warfarin.

Adult↗
PubMed1987

Protein C response to induction and withdrawal of oral anticoagulant treatment.

Protein C activity and antigen levels have been related to clotting activities of factors VII and X during the induction and withdrawal periods of oral anticoagulant treatment. Both factor VII and protein C activities fell rapidly during induction but factor VII showed a more rapid and much more marked depression than protein C. In contrast, reductions in factor X were much slower. Protein C antigen, although depressed rapidly at the initiation of treatment, did not subsequently fall to the same degree as protein C activity. The ratio of activity to antigen became progressively smaller. On discontinuation there was a reversal of the pattern but with two important differences. Firstly, there was evidence of an excessive rise ('rebound') of factor VII compared with the steady state levels in these patients; and secondly there was a surprisingly slow return of protein C to normal levels after the oral anticoagulant was withdrawn (levels were still below normal on day 4). These observations lend support to gradual withdrawal of oral anticoagulants after a period of long-term administration. The results suggest that after discontinuation of long-term anticoagulants patients may have increased coagulability up to four days.

Acenocoumarol↗
PubMed1986

Calibration of BCT/441, the ICSH reference preparation for thromboplastin.

An international collaborative exercise has been undertaken to calibrate a secondary international reference preparation (IRP) of thromboplastin on behalf of the International Committee for Standardization in Haematology (ICSH). This preparation of British Comparative Thromboplastin (BCT/441) is required because supplies of the WHO primary IRP (BCT/253) are necessarily limited. The calibration was performed at seven centres with only a small degree of interlaboratory variation. As a result of this study an ISI value of 1.04 has been assigned to the preparation. Opportunity was also taken to assess the reliability of a simplified calibration based on lyophilised plasmas. The results of the latter appeared reliable. BCT/441 will be available to officially designated National Control Laboratories for calibration of local thromboplastins to promote prothrombin time standardization in oral anticoagulant control.

Freeze Drying↗
PubMed1986

The reliability of activated partial thromboplastin time methods and the relationship to lipid composition and ultrastructure.

Wide variations in procoagulant properties, lipid composition and ultrastructure of five commonly used APTT methods have been demonstrated. Performance of the methods with a range of coagulation abnormalities has been ranked. Most of the reagents obtained a high score with one or more defects, but a low score with others. A consistent good ranking throughout was only observed with one reagent. The number of significant correlations between the reagents' procoagulant activities and lipid content confirms the view that the performance of an APTT method is largely dependent upon its lipid composition. Marked differences in concentration and distribution of phospholipids, fatty acids and neutral lipids were evident. The importance of the concentration of phosphatidyl serine in regulating the procoagulant activity of an APTT method has been demonstrated. Electron microscopy provides evidence of the contrasting composition of the reagents from the more discrete uniform liposomes present in the more reliable reagents, to more ill-defined components present in those reagents which performed less well. The study highlights the need for standardisation of the APTT.

Blood Coagulation Tests↗