Plasma thrombopoietin concentrations in response to platelet transfusion therapy

Absolute immature platelet count may predict imminent platelet recovery in thrombocytopenic children following chemotherapy

BACKGROUND

Immature platelets are the youngest circulating platelets and they reflect the rate of thrombopoiesis. The immature platelet fraction (IPF) or the absolute immature platelet count (AIPC) may predict platelet count recovery following chemotherapy-induced thrombocytopenia in pediatric patients and help guiding prophylactic platelet transfusion therapy.

PROCEDURE

To test IPF and AIPC as predictors of platelet recovery, 19 children with platelet nadirs of less than 20 × 10(9)/L after chemotherapy were prospectively enrolled. IPF, platelet count, and C-reactive protein (CRP) were analyzed in 416 paired samples from 37 patients with malignancies to test if IPF-levels were CRP dependent.

RESULTS

A significant increase of 0.6 × 10(9)/L in AIPC was seen between 1 and 2 days prior to platelet count recovery. No predictive day-to-day differences were found for IPF. Platelet count recovery did not occur significantly earlier for patients with a peak IPF > 10% than for those patients with a peak IPF < 10%. IPF and AIPC showed no correlation to CRP. AIPC was in contrast to IPF not influenced by platelet transfusions.

CONCLUSION

AIPC increased significantly between 24 and 48 hours before platelet recovery whereas IPF showed no significant increase during the same time period. AIPC may be a better indicator than IPF for predicting platelet recovery after chemotherapy in pediatric patients.

The role of thrombopoietin in the thrombocytopenia of patients with liver cirrhosis

OBJECTIVES

Thrombocytopenia is a common disorder among cirrhotics that has been traditionally explained by splenic platelet pooling and destruction. Thrombopoietin (TPO), the main stimuli for thrombopoiesis is produced primarily in the liver and degraded by circulating platelets, but its role in the thrombocytopenia of liver cirrhosis is not well understood. The main goal of this study is to clarify the role of TPO in the pathogenesis of thrombocytopenia in cirrhosis.

METHODS

The relation among TPO, platelet count, spleen size, portal hypertension, and liver function was studied in 33 cirrhotic patients before and after either partial splenic embolization or liver transplantation.

RESULTS

Cirrhotics with thrombocytopenia had lower serum TPO levels than healthy controls (median values (interquartile range: ICR) were 120.7 (42.0-191.6) vs 756.4 (527.0-965.1) pg/mL, respectively; p<0.001). Among cirrhotics with thrombocytopenia, serum TPO was related to spleen size (rho=-0.387, p=0.046), but not to platelet count as occurs physiologically. After partial splenic embolization, TPO and platelet count increased significantly and the physiological relation between TPO and platelet count was restored (rho=-0.665, p=0.026). Similar results were observed after liver transplantation.

CONCLUSIONS

Our results suggest that besides impaired production in the failing liver, an increased TPO degradation by platelets sequestered in the congested spleen may contribute to thrombocytopenia in cirrhotic patients.

In multiple myeloma increased thrombopoietin (Tpo) production may be involved in the maintenance of platelet production

In multiple myeloma (MM), suppression of haematopoiesis occurs as a result of expansion of malignant cells in the bone marrow. Thrombopoietin (Tpo) levels in patients with impaired platelet production are generally found to be highly elevated. To examine the circulating Tpo levels in patients with MM, Tpo levels were measured in 50 serum samples from 34 patients. Tpo levels were subsequently related to disease stage, and cell numbers and markers, i.e. platelet count, leukocyte count and haemoglobin (Hb) concentration. Elevated Tpo levels were found in association with decreased platelet counts (n=8), but also in patients with normal platelet counts (n=14). The latter group included patients without and with signs of impaired haematopoiesis, i.e. with decreased Hb concentration and decreased leukocyte count. These results show that neither platelet counts nor Tpo levels are reliable parameters to judge bone-marrow failure in patients with MM. Furthermore, in patients with MM, increased Tpo levels may play a role in the maintenance of thrombocytopoiesis. The origin of the increased Tpo levels remains to be determined.

Analysis of the kinetics of TPO uptake during platelet transfusion

BACKGROUND

It has been shown in several studies that platelets play a role in the removal of TPO from the circulation. For instance, in vitro studies have shown that platelets can bind and internalize TPO, and transfusion studies have shown that the concentration of circulating TPO decreased after platelet transfusion. In the current study, the in vivo kinetics of plasma TPO levels and TPO uptake by transfused platelets is analyzed in more detail.

STUDY DESIGN AND METHODS

Serial blood samples from patients who received a platelet transfusion were analyzed with respect to platelet count, plasma TPO concentration, and TPO content per platelet. In addition, the capacity of transfused platelets to bind TPO in vitro was assessed.

RESULTS

Platelet counts increased immediately after transfusion, but subsequently started to decrease. Conversely, TPO levels decreased significantly but then returned to baseline level by 44 hours after transfusion. Platelet count and plasma TPO concentration were inversely correlated (r(p) = -0.9; p<0.05). The decrease in TPO concentration upon transfusion was accompanied by a significant increase in the platelet-associated TPO concentration. After transfusion, platelets isolated from the patient still displayed functional TPO receptors, as indicated by their intact capacity to bind TPO in vitro.

CONCLUSION

The decrease in plasma TPO followed by the increase in platelet TPO provides evidence that platelets are responsible for the clearance of TPO in circulation. In vivo, platelets can bind and may degrade TPO upon platelet transfusion.