Reticulated platelets in primary and reactive thrombocytosis

Abstract

The recent paper by Cerutti et al (1997) compared serum thrombopoietin (TPO) levels in patients with essential thrombocythaemia (ET) and reactive thrombocytosis (RT). Although serum TPO levels were significantly elevated in both patient groups compared to normal controls, the results suggest that the assay cannot be utilized to distinguish between ET and RT. It would be interesting to determine whether these results are reproducible in plasma, as platelet release of TPO may occur during activation and clotting.Human TPO plays a critical role in regulating megakaryocytopoiesis and platelet production (Kaushansky, 1995), hence regulating the number of reticulated platelets (young platelets), which can be detected by flow cytometric analysis of platelet RNA. Evidence is accumulating suggesting that the number of reticulated platelets is not only a reflection of platelet production but can be used to differentiate ET from RT (Harrison et al, 1998). We have recently utilized a modified method to study reticulated platelets (Robinson et al, 1998) in patients with untreated ET (n ¼ 10), RT (n ¼ 10) and normal controls (n ¼ 11). The percentage of reticulated platelets was significantly elevated in ET when compared to RT or controls (P < 0·05) (Fig 1A), in agreement with previous studies. However, although the absolute numbers (Fig 1B) of reticulated platelets were identical in ET and RT (P ¼ 0·29), they were both significantly elevated when compared to controls (P < 0·05). These results suggest that the overall platelet production and turnover is elevated in ET but not in RT. This could be a reflection of the elevated TPO levels in ET observed by Cerutti et al (1997) and Taraha et al (1996). The reduced expression of the c-mpl receptor copy number and hence reduced TPO clearance as recently described (Horikawa et al, 1997), could explain these observations in ET. The elevated TPO levels in RT, however, do not result in a significant effect on platelet production as reflected in the percentage of reticulated platelets. The increased absolute count in RT is merely a reflection of the relationship between platelet count and the percentage of reticulated platelets which should theoretically be linear when platelet production is normal.This data provides support that the pathogenesis of the elevated platelet count in RT is different from ET, but is unlikely to be solely the result of increased TPO production as suggested by Cerutti et al (1997), as this would result in an elevated percentage of reticulated platelets. In summary, determination of platelet mRNA may prove to be a useful positive diagnostic tool in the differentiation of ET from RT. Larger studies correlating serum or plasma TPO levels and reticulated platelets in thrombocytosis will clarify the issue further.

Reticulated platelets: a reliable measure to reduce prophylactic platelet transfusions after intensive chemotherapy

“…Reference range values with these experimental conditions are in agreement with the literature data. 14,[24][25][26] Our inter-and intraassay CV rates are less than 10 percent in normal subjects and severe thrombocytopenic patients.…”

Reticulated platelets: analytical aspects and clinical utility

“…However, it also became evident that the flow cytometric assay was prone to methodological variation, which made it difficult to compare results obtained with different assays. For example, the normal reference range was reported to range between 1% and 15% [23,39]. This wide range can be explained by lack of standardization of the methods.…”

“…Kienast and Schmitz initiated a breakthrough in the field when they described a flow cytometric technique for analyzing retPLT, based on RNA staining by thiazole orange [15]. In subsequent years, several research groups published their findings in a wide variety of conditions like thrombocytopenia [16][17][18][19][20][21], thrombocytosis [22,23], after stem cell transplantation [24][25][26][27], hereditary platelet diseases [28,29], thrombo-embolic disorders [30,31], kidney disease [32][33][34], preeclampsia [35], hyperthyroidism [36] and in healthy and thrombocytopenic neonates [37,38]. The overall conclusion from these studies is that retPLT in blood represent a useful non-invasive marker of megakaryopoietic activity in the bone marrow.…”

“…Another well-documented application of retPLT is monitoring the thrombocytopenic phase after chemotherapy and transplantation for hematological malignancies Normal or high platelet count Thrombocytosis Estimating platelet turnover [22,23,96] ( Table 2). Generally, an increase in retPLT precedes the recovery of platelet count by 2-3 days.…”

Comparison of flow cytometry with the Sysmex XT2000iV automated analyzer for the detection of reticulated platelets in dogs

“…Standard flow cytometric detection of r‐PLT requires a flow cytometer and involves several precise manual preparation steps. Furthermore, measurement of r‐PLT is prone to high intra‐laboratory and inter‐laboratory variations 9,10 . Even though quantification of r‐PLT is an accepted method to evaluate thrombopoiesis in several disease states and to assess the myelosuppressive effect of chemotherapy in humans, 11,12 analysis of r‐PLT by flow cytometry has not become a routine test in medical laboratories.…”