This study showed that overall platelet counts were significantly increased in thrombocytopenic CHC patients after successful DAA treatment. BL TPO is positively associated with significant platelet count improvement and platelet count improvement ratio. BL TPO level > 120 pg/ml can predict significant platelet count improvement.
BL TPO can be positively associated with significant platelet count improvement and is correlated with platelet count improvement ratio at EOT and P12 (ρ = 0.282, P = 0.004 and ρ = 0.502, P < 0.001 at EOT and P12, respectively). This association may be related to the splenic size and fibrosis stage. Previous studies have demonstrated that a higher TPO is related to a smaller spleen size29,30 and less hepatic fibrosis.13–15, 19,31 In our study population, it was shown that those without splenomegaly had significantly higher TPO levels. However, analysis of the TPO levels between non-advanced and advanced fibrosis patient groups showed no significant difference. TPO alone may not truly reflect synthesis function of the liver because it is produced by the liver at a constant rate and removed from circulation by TPO receptors on megakaryocytes and platelets.32,33 Platelet turnover also affects TPO level. 3,34 We did not check platelet turnover; therefore, the low TPO level might be attributed to either poor liver function or high platelet turnover. Another likely reason is that we classified non-advanced or advanced hepatic fibrosis by the FIB4 score; some patients in the advanced fibrosis group may actually have non-advanced hepatic fibrosis. The actual reason requires further studies checking platelet turnover and using liver biopsy as a classification method for TPO level analysis in different fibrosis stages.
Though we knew baseline TPO was positively correlated to the platelet count change, the cut-off value was unclear. Therefore, we used ROC test and found the baseline TPO level > 120 pg/ml was associated with significant platelet count improvement. The sensitivity is 88.6%, and specificity is 71.7%, with accuracy being 78.8%. Hence, when thrombocytopenia is observed in untreated CHC patients, this cut-off value may be helpful in predicting who would have significant improvement after DAA therapy.
In the current study, BL TPO levels were not correlated with BL platelet count (ρ = 0.054, P = 0.587). This result was also corroborated by other studies. 19,29,30 It is reasonable to see this phenomenon because absolute platelet count is affected by TPO, spleen size, autoimmune status, megakaryocyte mass in bone marrow, and the aforementioned viral effect. 16,29 We also found that the TPO level (32–3944 pg/mL) in patients was more variable, compared to the normal population (81.3–237.7 or 19.25–377.75 pg/ml).29,35 This suggests that the ability of our patients to produce or destroy TPO differed significantly. Although some patients, with liver disease, had higher TPO levels, the elevation was mostly inadequate, compared with thrombocytopenic patients due to other diseases such as aplastic anemia or chemotherapy-induced thrombocytopenia. 31 In patients with early stage liver fibrosis, TPO production may increase to partly compensate for the decreased platelet count; those with more advanced fibrosis or liver cirrhosis produce relatively and inappropriately low TPO. 13–15, 19,31 Moreover, other factors such as hypersplenism, may offset the positive effect of elevated TPO. Congested spleen contains a large platelet mass, which would bind to, internalize, and destroy TPO. 30,36 We found that those with splenomegaly had significantly lower TPO than those without splenomegaly. A negative association between TPO level and spleen size was also reported by other studies,29,30 but there was a study revealing no correlation between them.19 These differences may be due to the relatively small number of cases in these studies and patient selection criteria.
This study found that the only factor associated with significant platelet count improvement was high BL TPO. Other BL characteristics were not related to such changes after DAA therapy. This was partly different from our previous study.8Our previous study showed that moderate to severe fatty liver and low BL platelet count could predict significant platelet count improvement. The most likely reasons were that some differences existed in the previous study, compared to findings of the present study, including more case numbers (n = 249), more cancer patients (n = 19 vs. n = 0, P = 0.001), viable HCC patients (n = 14 vs. n = 0, P = 0.013), more advanced hepatic fibrosis patients (n = 213 vs. n = 72, P = 0.001), and more moderate to severe fatty liver patients (n = 24 vs. n = 5, P = 0.2).
There are some limitations of our study. First, we did not perform biopsy of the liver in all patients to check inflammation and fibrosis severity. Instead, we used noninvasive indices such as the FIB-4 test, to identify patients with advanced fibrosis; this is a relatively reliable method. 22 Second, we did not perform bone marrow biopsy in this study to exclude possible indolent hematological disorders in our patients. Bone marrow biopsy is an invasive procedure, which could not be performed except with a clinically strong indication. Third, we did not check for platelet turnover. However, hypersplenism is the main contributor to platelet turnover in patients with splenomegaly,34 which were included in our study. In patients without splenomegaly, more evidence is required to clarify the association between platelet count and turnover, TPO level, and liver fibrosis severity. Fourth, other thrombopoietic cytokines such as interleukin-6, -11, and-3, were not evaluated. Their importance among these thrombocytopenic patients remains unknown. Therefore, further studies are needed.