The hematocrit value in polycythemia vera: caveat utilitor

Alterations to cavefish red blood cells provide evidence of adaptation to reduced subterranean oxygen

Animals inhabiting extreme environments allow the powerful opportunity to examine adaptive evolution in response to diverse pressures. One such pressure is reduced oxygen, commonly present at high-altitude and subterranean environments. Cave-dwelling animals must also deal with darkness and starvation, both of which have been rigorously studied as key forces driving the evolution of cave-associated traits. Interestingly, hypoxia as an environmental pressure has received less attention. Here we examined putatively adaptive phenotypes evolving in a freshwater teleost fish, Astyanax mexicanus, which includes both surface- and cave-dwelling forms. This model system also provides the opportunity to identify convergent responses to hypoxia, owing to the presence of numerous natural and independently-colonised cave populations, alongside closely-related surface conspecifics. The focus of this study is hemoglobin, an essential molecule for oxygen transport and delivery. We found that multiple cave populations harbor a higher concentration of hemoglobin in their blood, which is coincident with an increase in cave morph erythrocyte size compared to surface fish. Interestingly, both cave and surface morphs have comparable numbers of erythrocytes per unit of blood, suggesting elevated hemoglobin is not due to overproduction of red blood cells. Alternatively, owing to an increased cell area of erythrocytes in cavefish, we reason that they contain more hemoglobin per erythrocyte. These findings support the notion that cavefish have adapted to hypoxia in caves through modulation of both hemoglobin production and erythrocyte size. This work reveals an additional adaptive feature of Astyanax cavefish, and demonstrates that coordinated changes between cellular architecture and molecular changes are necessary for organisms evolving under intense environmental pressure.

Management Issues and Controversies in Low-Risk Patients with Essential Thrombocythemia and Polycythemia Vera

PURPOSE OF REVIEW

Essential thrombocythemia (ET) and polycythemia vera (PV) are the most common myeloproliferative neoplasms (MPNs). Treatment of ET and PV is based on the risk for subsequent thrombosis. High-risk patients, defined as older than 60, JAK2 V617F-positive patients, or patients with a history of prior thrombosis, merit cytoreduction to control blood counts, whereas a watchful waiting paradigm is utilized in low-risk patients. However, low-risk patients have a host of other specific management issues that arise during their disease course. This review will discuss the most common management issues specific to the care of low-risk patients, including anti-platelet therapy dosing, pregnancy, and indications for early cytoreduction.

RECENT FINDINGS

Although low-dose aspirin is well established in PV, its indications and dosing regimens are less clear in ET. Recent evidence has supported twice daily low-dose aspirin in ET and observation alone in very low-risk ET patients. Pregnancy is not contraindicated in MPNs, and we recommend aspirin throughout pregnancy with consideration for prophylactic postpartum anticoagulation. High phlebotomy needs, symptom burden, and extreme thrombocytosis are common reasons for initiation of cytoreduction in low-risk patients, although we typically do not start cytoreduction for an isolated high platelet count alone. Recent data has also demonstrated a potential disease-modifying effect of interferons in MPNs, with some experts now advocating the early use of interferon in low-risk patients, although more mature data is needed before practice guidelines change. We evaluate the literature to inform clinical decision-making regarding these controversies, including most recent data that has challenged the "watchful waiting" paradigm. Our discussion provides guidance on common clinical scenarios seen in low-risk ET and PV patients, who face a myriad of complex management decisions in their care.

The red blood cell count and the erythrocyte sedimentation rate in the diagnosis of polycythaemia vera

BACKGROUND

Iron deficiency in polycythaemia vera (PV) may impact the validity of the haematocrit (HCT), since HCT is red blood cell count (RBC) × mean corpuscular volume (MCV).

OBJECTIVES

To investigate (a) the effect of microcytosis on HCT, (b) the erythrocyte sedimentation rate (ESR) as a possible additional diagnostic marker for PV.

MATERIAL AND METHODS

This study included 182 subjects: 39 with PV, 27 with essential thrombocythemia (ET) and 116 suspected of myeloproliferative neoplasm (MPN) with a secondary cause for either thrombocytosis or erythrocytosis.

RESULTS

Patients with PV had significantly lower ratio of MCV and serum ferritin compared to MPN suspects. A good correlation of RBC versus HCT was found for PV and MPN subjects when individuals with microcytosis were excluded (R²  = .87 in PV and R²  = .82 in MPN suspects). We found a specificity of 98% and a sensitivity of 37% for ESR <2 mm in the diagnosis of PV.

CONCLUSION

The RBC may more precisely reflect the total red cell mass and accordingly the hypercoagulable state of the PV patient, which is integrated in the ESR. A combination of RBC and ESR is proposed as a novel tool to substitute the Hb concentration and the HCT in the diagnosis of PV.

Distinguishing essential thrombocythemia JAK2V617F from polycythemia vera: limitations of erythrocyte values

Distinguishing essential thrombocythemia JAK2V617F from polycythemia vera is difficult because of shared mutation and phenotypic characteristics. The World Health Organization suggested hemoglobin and hematocrit values to diagnose polycythemia vera (PV), but their sensitivity and specificity were not tested. Moreover, red cell values do not accurately predict red cell mass, which we use to discriminate essential thrombocythemia JAK2V617F from PV. Eighty-three PV and 39 essential thrombocythemia JAK2V617F patients were diagnosed based on JAK2V617F positivity, chromium-51 red cell mass, and marrow biopsy findings. Red cell values used to construct a receiver operating characteristic analysis determined optimal thresholds for distinguishing essential thrombocythemia JAK2V617F from PV. Red cell value frequencies were plotted determining if overlap existed. Chromium-51 red cell mass separated PV from essential thrombocythemia JAK2V617F, but red cell values overlapped in 25.0-54.7%. Our data indicate that a significant proportion of PV patients may be underdiagnosed by using only red cell values. A bone marrow biopsy was performed in 199 of 410 (48.5%) and a serum erythropoietin value was measured in 225 of 410 (54.9%) of potential PV patients at our institution. Without isotope studies, marrow biopsies and serum erythropoietin values should improve diagnostic accuracy and become mandatory, but clinical data suggest these tests have not been routinely performed. Therefore, the clinical hematologist must be aware of imperfect accuracy when using only red cell values for distinguishing essential thrombocythemia JAK2V617F from PV.

Hepcidin agonists as therapeutic tools

Hepcidin agonists are a new class of compounds that regulate blood iron levels, limit iron absorption, and could improve the treatment of hemochromatosis, β-thalassemia, polycythemia vera, and other disorders in which disrupted iron homeostasis causes or contributes to disease. Hepcidin agonists also have the potential to prevent severe complications of siderophilic infections in patients with iron overload or chronic liver disease. This review highlights the preclinical studies that support the development of hepcidin agonists for the treatment of these disorders.