Standardized flow cytometric method for the accurate determination of platelet counts in patients with severe thrombocytopenia

Determination of Serotonin Concentration in Single Human Platelets through Single-Entity Electrochemistry

This research introduces a method to directly detect serotonin in a single platelet through single-entity electrochemistry. Platelets isolated from human blood were analyzed by cyclic voltammetry and current-time measurements. When a single platelet collides with an ultramicroelectrode, serotonin inside the platelet is oxidized at the electrode surface, and an anodic current peak is consequently observed during measurement. The concentration of serotonin can be determined by integrating this peak current. In addition, this method can be used to determine the platelet concentration. Analysis of the collision frequency of platelets can provide information about the platelet concentration in the blood. As a result, platelet levels and serotonin concentrations in single platelets can be measured quickly and easily.

Trp53 regulates platelets in bone marrow via the PI3K pathway

The p53 gene is well known as a key tumor suppressor gene; it is vital for hematopoietic stem cell differentiation and growth. In the present study, the change of platelets (PLTs) in p53 knockout mice (p53^-/- mice) was investigated. The peripheral blood cell subsets and PLT parameters in p53^-/-mice were compared with those in age-matched p53^+/+ mice. Bleeding time as well as the alteration of PLT levels, were analyzed with the PLT marker CD41 antibody using flow cytometry. The results revealed that the number of PLTs in p53^-/- mice was significantly lower than that in p53^+/+ mice. Bleeding time was prolonged in the peripheral blood of p53^-/- mice compared with that of p53^+/+ mice. Furthermore, the related gene expression of the PI3K signaling pathway in the bone marrow of p53^-/- mice was shown to be associated with plateletogenesis. PI3K inhibitor (LY294002) was also used to treat p53^-/- mice, and the results demonstrated that LY294002 revert the change of PLTs in these mice. In summary, PLTs were altered in p53^-/- mice, and the PI3K signaling pathway was involved in that process, suggesting that the p53-dependent PI3K signaling pathway is involved in thrombocytopenia or PLT diseases. PLT number is reduced in p53 deficiency; however, this reduction could be reverted by inhibiting the PI3K pathway.

Platelets in the paediatric population: the influence of age and the limitations of automation

Accurate and precise platelet counting is important for the clinical management of children with platelet disorders. Current automated technologies are often unable to discriminate platelets from non-platelet particles particularly in circumstances where platelet anisocytosis is common. This study compares manual methodology and the automated technologies; impedance, optical density and CD61 immunoplatelet method (available on the Cell Dyn 4000) with the reference method of flow cytometric analysis in a paediatric population. A total of 141 samples were analysed and divided into specific age related groups and groups with thrombocytopenia and thrombocytosis. Data analysis showed that the CD61 method compared best with the reference method and this was evident in all the specified groups. The mean platelet count obtained by optical and manual methods were lower, suggesting that these methods are less reliable. The impedance count method was accurate despite its limitations. Strong correlations were observed in the 2-14 year age group but there was greater variation in the <1 month group supporting the theory that there is a greater variation in platelet characteristics in neonates. The CD61 method is the automated method of choice and would be particularly useful in the problem groups (platelet counts <50 x 10(9)/l and neonates <1 month old).

Quantitation of platelet aggregation and microaggregate formation in whole blood by flow cytometry

Platelet aggregation and microaggregate formation were measured in samples of stirred whole blood by flow cytometry. Blood samples were stirred in a multi-sample agitator with ADP, fixed and labelled with a platelet-specific CD42a-FITC fluorescent antibody. The blood was then diluted and applied directly to a flow cytometer. Platelets were identified using a gating procedure based on their expression of CD42a and then quantified. Aggregation was monitored as a fall in the number of single platelets. Both reversible and irreversible aggregation responses to ADP were determined and these were found to correlate directly with aggregation responses determined using a well-established single platelet counting technique using the Ultra-Flo 100 Whole Blood Platelet Counter. We found from flow cytometry that ADP-induced aggregation was coupled with a transient formation of platelet microaggregates over the initial 60 s following ADP addition. Assessment of single platelet loss by flow cytometry was found to be a reliable way of monitoring aggregation responses and provided new information on rapid microaggregate formation in ADP-stimulated blood.

Immunoplatelet counting: potential for reducing the use of platelet transfusions through more accurate platelet counting

Research is required to determine the optimal approach for prophylactic platelet transfusions in patients with haematological malignant disorders. It has been suggested that thresholds for prophylactic platelet transfusions of platelet counts below 10 x 109/l should be investigated, as these may be equivalent in clinical effectiveness and associated with lower costs and fewer complications. An important concern in such investigation is the accurate estimation of platelet counts below 10 x 109/l. This study aimed to further examine the potential reduction in platelet usage that could be made if a lowered platelet transfusion threshold of 5 x 109/l was used in conjunction with an immunoplatelet counting method. Clinical and laboratory data from 130 haematology patients were used. Standard platelet counting was performed using Bayer H3 and ABX Argos analysers. Immunoplatelet counting was performed by flow cytometry using anti-CD61. The potential for reducing platelet transfusions included consideration of clinical criteria that influence prophylactic platelet transfusion use. The results indicated that the use of an immunoplatelet count with a 5 x 109/l platelet transfusion threshold would potentially reduce the number of transfusions by 10.4% in comparison with a 10 x 109/l threshold and standard automated platelet counting with the ABX Argos analyser, and increase the number of transfusions by 5.4% in comparison with the same threshold using the Bayer H3 analyser. The immunoplatelet count may aid the clinical decision to transfuse platelets, but would not necessarily lead to a reduced use of platelet transfusions.

Automated CD61 immunoplatelet analysis of thrombocytopenic samples

Revision of the current decision point for prophylactic platelet transfusion in thrombocytopenic patients requires the availability of a method that is able to provide accurate platelet counts to as low as 1 x 109/l. This study is the first to evaluate the immunoplatelet method (CD61-Imm) of the haematological analyser Cell-Dyn 4000 in direct comparison with the flow cytometric procedure. Additionally CD61-Imm results were compared with CD4000 optical (Plto) counts in the ranges 20-547 x 109/l (n = 127) and 1-35 x 109/l (n = 107). The immunoplatelet and Plto results were in good agreement between 20 x 109/l and 547 x 109/l, but for samples of < 25 x 109/l the Plto tended to overestimate the counts. We determined the limits of detection (LD) and quantification (LLQ) for all three methods using standard statistical procedures. The LD for the flow cytometric CD41a method was 0.02 x 109/l compared with 0.009 x 109/l and 1.73 x 109/l for the CD61-Imm and Plto methods respectively. The LLQCV = 15% for the CD41a method was 1.8 x 109/l compared with 1.6 x 109/l and 18.0 x 109/l for the CD61-Imm and Plto procedures. In conclusion, (i) the CD61-Imm method performance is at least equivalent to the reference flow cytometric method, and (ii) in severe thrombocytopenia the CD61-Imm count is superior to the Plto count.