Paula Wessels

A computer program in compiled basic for the IBM personal computer to calculate the mean platelet survival time with the multiple-hit and weighted mean methods

We developed an easy-to-operate computer program for the IBM personal computer to calculate, display and store in a database platelet kinetic data determined by analysis of the rate of clearance of radiolabeled blood platelets from the circulation. This was done by curve fitting using the weighted mean method and multiple-hit model. These models are complementary and calculating the mean platelet survival time with both is recommended. Improvement of the weighted mean method was investigated. The optimized weighting and fitting the exponential function with the Marquardt non-linear least squares method improved the weighted mean method. The weighted mean and multiple-hit models fit the survival curve data equally well. The calculation of the mean platelet survival time with the weighted mean method was very fast. The duration of calculation with the multiple-hit model could take up to 2 minutes. Calculation of the mean platelet survival time using both models has the advantage that conditions when calculation of the mean platelet survival time would be invalid, can be detected. The computer program will promote the valid comparison of results obtained at different institutions.

An improved method for the quantification of the in vivo kinetics of a representative population of 111In-labelled human platelets

The recommended and commonly used methods for the isolation of platelets from whole blood do not harvest a representative platelet population. There is evidence that these methods may result in the loss of a functionally more active platelet subpopulation. We describe a method whereby a completely representative population of platelets was isolated from the whole blood of 28 normal human volunteers by repeated washing of platelets from the red-cell layer. The harvesting efficiency was 98.3%±2.8%. The platelets were labelled with 111In-oxine in a saline milieu with a labelling efficiency of 86.4%±6.8%. The disappearance of reinjected labelled autologous platelets from the circulation was almost linear, and the mean platelet survival was estimated to be 224±23 h. At equilibrium, 61%±12% of the labelled platelets were recovered from the circulation. The in vivo distribution at equilibrium and the sites of sequestration of the senescent labelled platelets were determined by geometric-mean whole-body quantification in six of the volunteers. This improved method permits accurate quantification of organ 111In radioactivity. Following reinjection, the labelled platelets pooled in the spleen and the accumulated activity can be presented by a single exponential function. At equilibrium, 31.1%±6.1% and 9.6%±1.2% of the platelets were in the spleen and liver, respectively. Splenic and hepatic radioactivity increased significantly with time, and at the end of the platelet life span, 35.6%±9.7% and 28.7%±8.3% of the labelled platelets were sequestrated in these organs, respectively. The 30.3%±7.8% remaining platelets were probably sequestrated mainly in the reticuloendothelial component of the bone marrow and other tissues. These techniques of platelet labelling and measurement of the in vivo distribution of 111In-labelled platelets are relatively simply and accurate methods for the study of platelet kinetics in man.

Kinetics, in vivo redistribution and sites of sequestration of indium-111-labelled platelets in giant platelet syndromes.

Six patients with giant platelet syndrome were examined: four with Bernard‐Soulier syndrome (two were asplenic); one with hereditary thrombopathic thrombocytopenia; and one with May‐Hegglin anomaly. Autologous platelets were labelled with In‐111‐oxine and in vivo redistribution and sites of sequestration measured with quantitative imaging. In Bernard‐Soulier syndrome platelet survival was normal or moderately shortened; platelet turnover was decreased only in the two patients with thrombocytopenia. In the patients with thrombopathia or May‐Hegglin anomaly, platelet survival and turnover was moderately decreased. In those patients with normal‐sized spleens, the mean splenic platelet pool consisted of 35.5% of the platelet mass, i.e. normal. The intrasplenic transmit time of the megathrombocytes was prolonged. Splenic blood flow was within normal limits. There was a marked accumulation of platelets in the liver at equilibrium: 15.5‐58.8% of whole body radioactivity (normal 9.6±1.2%). This finding is unexplained. The final sites of sequestration of platelets were mainly in the liver and spleen, similar to that seen in normal subjects. We conclude that there is no inverse relationship between cell size and splenic platelet transit time. Platelet size therefore does not determine the size of the splenic platelet pool. The size of the platelets also does not seem to affect the sites of sequestration at the end of their life span.

Evaluation of Models to Determine Platelet Life Span and Survival Curve Shape

The value of radionuclide platelet survival studies to delineate the mechanisms of thrombocytopenia and factors contributing to it has been proven (1), and the effect of various diseases and therapies on platelet survival may be evaluated by the same technique. The recent introduction of 111In-oxine as a cellular label allowing in vivo imaging of platelet distribution, has renewed interest in platelet kinetic studies (2,3).