Effect of pH and buffering condition on dMPV of three types of platelet concentrates.

Normal platelets display a log normal size distribution pattern when analysed by an automated cell counter. Considerable changes in the platelet size distribution occurs during collection, processing and storage. This is easily monitored by the variation seen in the cellular indices or size distribution patterns. Platelet activation leads to a shift to the right whereas discoid/spheric conversion and microvesiculation/fragmentation are associated to shift to the left. Therefore changes in cellular indices are of value in assessing the dynamic shape changes and aggregation/disaggregation that platelet undergo during storage. We describe here an objective method for measuring platelet functional integrity based on cell counting. Our procedure is simple and based on the measurement of difference (d) of MPV before and after the addition of platelet samples to EDTA (4 ml dry dipotassium EDTA tube), incubating at 22 degrees C for a period of 1 h (for optimisation of shape changes and disaggregation) before counting. Since the platelet functional activity/aggregation states are pH-dependent we have investigated the effect of buffering condition on the functional integrity measured by dMPV. Both the standard and buffered EDTA exposure procedures appear to be suited for monitoring platelet functional integrity/aggregation and activation states but the standard EDTA protocol eliminates the need for pH determination hence is our preferred diagnostic tool, for platelet functional integrity and aggregation states.

Characteristics of platelet concentrates, with particular reference to Autopheresis C Plateletcell: correlation between dMPV and other tests for platelet function.

The quality of platelet concentrates (PC) collected by the Autopheresis C cell separator was assessed in two Regional Transfusion Centres taking part in a multicentre study. This study also enabled the assessment of a new simple, rapid test of platelet function and comparison with more established tests, such as aggregation to adenosine diphosphate, as a tool for the quality testing of PC. The new test, based upon the measurement of mean platelet volume using automated haematological cell analysers, is rapid and uses the same samples as those used to estimate the platelet and leucocyte content of the concentrates. The high correlation between this test and the other tests of platelet function used in the study suggests that it is an ideal tool in the quality testing of platelet concentrates.

An international and interregional comparison of haemostatic variables in the study of ischaemic heart disease. Report of a working group.

Levels of haemostatic variables that may be involved in thrombogenesis have been compared in groups of men of similar mean age in communities at very low (Gambia), high (England and Czechoslovakia) or very high (Scotland and Finland) risk of ischaemic heart disease (IHD). There was a consistent gradient of higher factor VII levels with higher IHD risk and also suggestive gradients in the case of two other vitamin K dependent factors, factors II and X. Mean platelet counts were lower and mean fibrinolytic activity was greater in Gambian men than in European men. There was a suggestive though not entirely consistent association between mean fibrinogen levels and IHD risk in the groups from IHD-endemic countries. The results as a whole, and particularly those on factor VII, strengthen the case for the increasingly detailed epidemiological as well as laboratory investigation of the role of the haemostatic system in thrombogenesis and IHD.

Fibrinogen: a possible link between social class and coronary heart disease.

Mortality from coronary heart disease in civil servants in the lowest grade of employment has been found to be about three times that of men in the highest grade of employment. As part of an investigation of this finding several haemostatic variables were measured in a sample of 29 men in lower grades of employment and 45 men in higher grades. There was a significant difference in plasma fibrinogen concentrations between men in lower grades of employment and those in higher grades (mean 3.39 g/l v 2.95 g/l, respectively; p less than 0.01) but not in other haemostatic variables. Multiple regression analyses showed significant independent associations of fibrinogen concentration with smoking (p less than 0.05) and grade of employment (p less than 0.05). The size of the observed difference between the grades of employment was similar to that between those dying of coronary heart disease or surviving during longitudinal study; it may therefore be an important part of the mechanism underlying social class differences in coronary heart disease. The statistical relation between fibrinogen concentrations and other characteristics that may be concerned in the aetiology of coronary heart disease was examined. A summary measure of job stress was significantly related to fibrinogen concentration (p less than 0.01) and made a substantial contribution to explaining the differences between grades of employment. Behaviour type and a score of physical activity were not significantly related to fibrinogen concentration.

The effect of physiological levels of fibrinogen on platelet aggregation.

Results from the Northwick Park Heart Study (NPHS) suggest that physiological levels of plasma fibrinogen may influence platelet aggregability. This possibility has been further studied by the addition of purified fibrinogen to the blood of 17 study participants with low plasma fibrinogen levels. The results, which were highly consistent between different individuals, showed that fibrinogen increases aggregability as measured by the ADP ED50, the dose of adenosine diphosphate at which aggregation proceeds at half its maximum velocity. However, an increasing plasma fibrinogen level was associated with decreasing aggregability measured by another parameter, the ADP EMR (estimated maximum response). Although the balance of evidence is that the plasma fibrinogen level enhances aggregability, these conflicting results emphasize the limitation of any simple concept of "platelet aggregability".

Methods in dose response platelet aggregometry.

A standardized method for performing dose response platelet aggregation has been developed, and has been used in about 1000 subjects in a large prospective study of ischaemic heart disease. A computer program has been used to fit a sigmoidal relationship between primary aggregation response rate and the log dose of aggregating reagent. Estimates of the parameters of the sigmoid curve are used to characterize an individual's platelet aggregability. Methods for investigating the maintenance of long-term quality control have also been developed.

Sources of variability in dose response platelet aggregometry.

An experiment designed to assess the components of variability of a number of measures of platelet aggregability showed that the ADP ED50 (the estimated dose of adenosine diphosphate at which primary aggregation occurs at half its maximum velocity) had the least method error of any of the parameters measured, but that none had a very high between-person component of variability. A simultaneous comparison of a syringe technique and a free-flowing technique for venepuncture revealed no differential effects on the aggregation parameters measured. An enforced increase in the stirring speed in the aggregometer led to an experiment which showed that such a change did not apparently affect the ED50s.

Epidemiological characteristics of platelet aggregability.

The epidemiological characteristics of platelet aggregability were established in 958 participants in the Northwick Park Heart Study. The main analyses were based on the dose of adenosine diphosphate at which primary aggregation occurred at half its maximum velocity. Aggregability increased with age in both sexes, was greater in whites than blacks (particularly among men), and tended to decrease with the level of habitual alcohol consumption. Aggregability was, however, greater in women than men and in nonsmokers than smokers. There was no relation between aggregability on the one hand and obesity, current or past oral contraceptive use, menopausal state, or blood cholesterol and triglyceride concentrations on the other. Aggregability was somewhat, though not significantly, higher in men with a history of ischaemic heart disease and in those with electrocardiographic evidence of ischaemia than in those without. There was a strong association between the plasma fibrinogen concentration and aggregability. The widely held concept of platelet aggregability and its implications is probably an oversimplification. In the prevention of thrombosis it may be as useful to consider modifying external influences on platelet behaviour, such as plasma fibrinogen concentration or thrombin production, as it is to rely solely on platelet active agents.