Antonio Ordinas

Experimental basis for the use of red cell transfusion in the management of anemic-thrombocytopenic patients

The Baumgartner perfusion technique was used as an experimental model to study the combined influence of red cell (RBC) and platelet counts on the interaction of platelets with the subendothelium. At normal hematocrit and a platelet count of 100,000 per microliter, platelet adhesion and platelet aggregate (PAG) formation on subendothelium were statistically decreased. At lower platelet counts (50,000/μliter), there was an even more marked reduction in the formation of PAGs. The critical role of RBCs was demonstrated in experiments at low hematocrit; the formation of PAGs was impaired in perfusions at 20 percent hematocrit at any platelet count tested. Platelet deposition on subendothelium was almost absent at 50,000 platelets per μliter, suggesting a negative synergistic effect for the association of low hematocrit (20%) with a low platelet count. Perfusion experiments carried out with nonanticoagulated blood drawn directly from anemic patients with mild thrombocytopenia (43,000–58,000 platelets/μliter) before and after RBC transfusion were in agreement with previous experiments that indicated that normalization of both platelet count and hematocrit is required to achieve optimum hemostasis. Our data give experimental support for the transfusional management of patients with anemia and thrombocytopenia.

Platelet contribution to the formation of metastatic foci: the role of cancer cell-induced platelet activation.

Platelets are thought to be involved in the development of blood borne metastasis. Ultrastructural and experimental studies demonstrate that association between tumor cells and platelets with subsequent activation of the coagulation cascade takes place in malignancy. Several hypotheses have been proposed to explain the mechanisms by which tumor cells activate platelets including generation of thrombin, ADP release and involvement of arachidonate metabolism. Perfusion studies with human homologous systems showed that intact tumor cells and tumor cell microvesicles were able to induce platelet thrombogenicity under defined flow conditions. The presence of divalent cations and plasma factors was necessary for the cancer cells to exert their activating capacity. These results suggest a role for platelets in the development of secondary metastasis as well as in the thrombotic events of malignancy.

Fibronectin is required for platelet adhesion and for thrombus formation on subendothelium and collagen surfaces

Fibronectin (FN) plays a role in several adhesion mediated functions including the interaction of platelets with subendothelium. We investigated the role of plasma FN in platelet adhesion and platelet thrombus formation under flow conditions. We used two different perfusion models: the annular chamber with alpha-chymotrypsin-treated rabbit vessel segments, and the flat chamber with coverslips coated with fibrillar purified human collagen type III. Perfusates consisted of washed platelets and washed RBCs, suspended in normal or FN-depleted plasma. Perfusions were carried out for ten minutes at shear rates of 300 or 1,300 s-1. Platelet deposition and thrombus dimensions were evaluated morphometrically by a computerized system. We found that depletion of plasma fibronectin significantly reduced the percentage of total coverage surface and percentage of platelet thrombus, at both shear rates studied, and in both perfusion systems (P less than .01) (P less than .01). The dimensions of the platelet thrombi formed in perfusions at high shear rate were also significantly reduced in perfusions carried out with FN depleted plasma (P less than .01). Addition of purified FN to FN-depleted perfusates restored all values to those measured in the control perfusions. These results indicate that plasma FN is required for platelet aggregate and thrombus formation following adhesion under flow conditions.

Increased local procoagulant action: a mechanism contributing to the favorable hemostatic effect of recombinant FVIIa in PLT disorders

BACKGROUND: Recombinant FVIIa (rFVIIa) has been shown to improve hemostasis in patients with thrombocytopenia and to prevent or control bleeding episodes in patients with inherited deficiencies of major PLT glycoproteins, but the mechanism of action is not well understood.

Platelet-specific antibodies in HLA-immunized patients receiving chronic platelet support

BACKGROUND : In HLA‐alloimmunized patients, the unexpected failure of HLA‐matched platelet transfusions usually raises the suspicion about concomitant platelet‐specific antibodies. As the reported frequency of platelet‐specific antibodies in multitransfused patients varies widely, the aim of this study was to determine the prevalence of such antibodies in a population of chronic thrombocytopenic patients with HLA antibodies.

Platelet concentrates prepared and stored under currently optimal conditions: minor impact on platelet adhesive and cohesive functions after storage

BACKGROUND: The effect on platelets of two standard methods of platelet concentrate (PC) preparation was studied by flow cytometry. The findings were correlated with those obtained in an experimental in vitro perfusion model.

Effect of recombinant human erythropoietin treatment on circulating reticulated platelets in uremic patients: Association with early improvement in platelet function

Recombinant human erythropoietin improves platelet function in uremia through the correction of anemia, but this effect can be seen also before the hematocrit rise. We studied 12 hemodialyzed patients (seven men, five women) who received recombinant human erythropoietin (40 IU kg−1 i.v., three times weekly) and were evaluated before treatment and after three doses; 24 control subjects were used. Platelet aggregation induced by adenosine 5′‐diphosphate (ADP), epinephrine, collagen, arachidonic acid, and ristocetin, and reticulated platelets determined by flow cytometry after staining with thiazole orange were measured. Platelet aggregation induced by all the agonists were impaired in uremic patients (P < 0.01), but ADP and ristocetin‐induced aggregations improved after treatment (P < 0.01). Hemodialyzed patients had less reticulated platelets than controls (P < 0.01). Reticulated platelets increased after three doses of treatment (P < 0.01). In conclusion, improvement of platelet function at early stages of recombinant human erythropoietin treatment may be attributed to the increase in young platelets detected as reticulated platelets. Am. J. Hematol. 59:105–109, 1998.

Growth of bacteria in platelet concentrates obtained from whole blood stored for 16 hours at 22°C before component preparation

BACKGROUND: Previous studies have shown that cooling whole blood to 22°C immediately after collection allows it to be held for up to 16 hours before component preparation (overnight‐hold method) without a significant decrease in the quality of components obtained. A study was designed to evaluate the effect of the overnight‐hold method on the growth of bacteria in experimentally contaminated blood units.

Hemostasis in patients with severe von Willebrand disease improves after normal platelet transfusion and normalizes with further correction of the plasma defect

BACKGROUND: A defective hemostatic effect of plasma concentrate infusion in patients with severe von Willebrand disease (vWD) has been ascribed to the absence of platelet von Willebrand factor (vWF) STUDY DESIGN AND METHODS: The role of platelet vWF in hemostasis of severe vWD was investigated. A plateletpheresis unit (4‐5 × 10(11) platelets) from a normal compatible donor was transfused before any cryoprecipitate infusion to three type 3 vWD patients and to one patient with severe type 1 vWD with low levels of platelet vWF who required replacement therapy for bleeding episodes. Autologous platelets were transfused to one of the patients with type 3 vWD. RESULTS: Partial corrections of bleeding times (14‐17 min vs. baseline>30 min) were observed in all patients after the transfusion of normal platelets. During cryoprecipitate infusion, bleeding times were normalized (<6 min), and bleeding episodes stopped when plasma levels of vWF activity ranged from 14 to 18 U per dL. Platelet interactions with the subendothelium increased in parallel with the correction of bleeding times. These results indicate that if approximately 20 percent of the total number of platelets have normal vWF antigen and if plasma vWF levels are at least 14 U per dL, then bleeding times will normalize and mucosal hemorrhages will stop. Transfusion of autologous platelets in one patient with type 3 vWD did not modify bleeding times or platelet adhesion on the subendothelium. CONCLUSION: The hemostatic effect of normal platelets in type 3 vWD seems to be related to the platelet vWF in the transfused platelets.

Clinical and laboratory factors associated with platelet transfusion refractoriness: a case–control study

In recent years clinical factors have largely surpassed alloimmunization as the predominant cause of platelet refractoriness. This makes it necessary to properly identify and weigh the non‐immune factors that have a major impact on refractoriness. A case–control study is suitable for such an analysis, and to our knowledge has not previously been performed to assess this issue.