Continuing Education Activity

Polycythemia is characterized by an increased red blood cell mass and is typically identified clinically by elevated hemoglobin concentration and hematocrit. Clinical manifestations are often nonspecific and relate to impaired microvascular flow and blood hyperviscosity, with complications that include arterial and venous thrombosis, paradoxical bleeding, and progressive symptom burden. Classification includes relative (spurious) polycythemia from plasma volume contraction and true polycythemia, which is further divided into primary causes (eg, polycythemia vera with Janus kinase 2 [JAK2] mutations and low erythropoietin levels) and secondary causes driven by elevated erythropoietin (eg, hypoxemia-related cardiopulmonary disease, high-altitude exposure, renal pathology, and erythropoietin-secreting tumors). Evaluation proceeds sequentially with a hemogram, serum erythropoietin level, targeted assessment for hypoxemia and related secondary etiologies, and bone marrow examination when diagnostic criteria warrant.

Course participation enables improved recognition and workup of polycythemia, including differentiation between primary and secondary forms, appropriate use of erythropoietin testing and JAK2 mutation assessment, and selection of evidence-based management strategies, such as hematocrit targets for phlebotomy, antiplatelet therapy when indicated, and cytoreductive treatment for high-risk polycythemia vera. Learners strengthen skills in identifying high-risk features for thrombosis and bleeding, interpreting laboratory abnormalities (eg, leukocytosis, thrombocytosis, iron deficiency), and monitoring for disease progression. Patient outcomes improve when care is coordinated within an interprofessional team: clinicians integrate diagnostic and therapeutic decisions; pharmacists optimize medication selection, dosing, and interaction monitoring; nurses provide education, symptom surveillance, and care coordination; and phlebotomists support safe and consistent hematocrit control. Clear communication and shared documentation across disciplines enhance safety, continuity, and quality of care.

Objectives:

• Differentiate relative (spurious) polycythemia from true erythrocytosis based on clinical context and laboratory findings.
• Assess thrombotic, hemorrhagic, and symptom burden risk to select evidence-based management strategies (eg, hematocrit targets for phlebotomy, antiplatelet therapy when indicated, and cytoreductive therapy for high-risk polycythemia vera).
• Develop longitudinal monitoring plans to improve detection of complications and disease progression (eg, postpolycythemia myelofibrosis or leukemic transformation) and implement structured follow-up.
• Implement interprofessional team strategies to improve care coordination and communication in the evaluation and long-term management of patients with polycythemia.

Introduction

Polycythemia, also called erythrocytosis, refers to an increase in the absolute red blood cell (RBC) mass in the body. Clinically, this is reflected by elevated hemoglobin or hematocrit levels relative to age- and sex-specific reference ranges. The reference RBC mass does not usually exceed 36 mL/kg in men and 32 mL/kg in women. Historically, red cell mass was measured, but current practice relies on hemoglobin and hematocrit for diagnosis. The reference ranges for normal hemoglobin and hematocrit vary by altitude, ethnicity, and country.[1] However, for reference, the hemoglobin and hematocrit values for a healthy adult man are 16 g/dL ± 2 g/dL and 47% ± 6%, respectively. The hemoglobin and hematocrit of a menstruating adult woman are usually 13 g/dL± 2 gm/dL and 40%± 6%, respectively. Polycythemia in newborns is defined as a central venous hematocrit greater than 65% or a hemoglobin value greater than 22 g/dL.[2]

Polycythemia vera is a subtype of polycythemia. Often colloquially referred to as polycythemia, polycythemia vera is an acquired, Philadelphia chromosome–negative myeloproliferative disorder.[3] This condition can be associated with overproduction of all 3 cell lines, with a notable predilection for red blood cells. The manifestations of erythrocytosis, regardless of cause, typically stem from the associated risks of blood hyperviscosity, including thrombotic events. Paradoxically, bleeding events are also frequently reported. Additionally, the rare risk of leukemic transformation, particularly after long-term cytotoxic therapy, may influence management.

Etiology

Classification

Polycythemia can be categorized as primary or secondary.

Spurious Polycythemia

Spurious polycythemia results from plasma volume contraction rather than an increase in accurate RBC mass. Causes include:

• Severe dehydration due to isolated fluid loss: increased hemoglobin and hematocrit may reflect diarrhea or severe vomiting.
• Gaisböck syndrome (stress or relative polycythemia): A controversial entity characterized by hemoconcentration associated with hypertension, smoking, obesity, or diuretic use.[3]

True Polycythemia

True polycythemia is further stratified based on serum erythropoietin (EPO) levels.

Low serum EPO levels (primary polycythemia):

• Polycythemia vera
• Primary familial and congenital polycythemia

High serum EPO levels (secondary polycythemia):

• Altitude
• Respiratory disorders: Chronic obstructive pulmonary disease, obesity hypoventilation syndrome (formerly Pickwickian syndrome), uncontrolled asthma
• Cyanotic heart diseases: Right-to-left shunts
• Renal disorders: Renal cysts, kidney cancer, renal artery stenosis
• Elevated carboxyhemoglobin: Usually seen in individuals who smoke tobacco or those with occupational exposure (working on cars in enclosed spaces or in broiler rooms)
• Hemoglobinopathies: High-affinity hemoglobins such as hemoglobin Yakima (a rare, inherited hemoglobin variant with high oxygen affinity)
• EPO-secreting tumors: Hepatocellular carcinoma, uterine leiomyomas, and cerebellar hemangioblastomas
• Iatrogenic causes: Erythropoietin analog administration, anabolic steroids, or testosterone replacement therapy

Neonatal Polycythemia

• Neonates typically have higher hematocrit levels than adults; this increase is a normal compensatory mechanism in newborns due to relative intrauterine tissue hypoxia. Neonatal polycythemia is exacerbated by the high affinity of fetal hemoglobin for oxygen.

Epidemiology

The prevalence of polycythemia vera is approximately 22 cases per 100,000 population.[4] No consistent or clinically meaningful differences in incidence have been demonstrated across racial or ethnic groups. Polycythemia vera shows a slight male predominance (male-to-female ratio approximately 1.2 to 1.5:1). Polycythemia vera is most commonly diagnosed after age 50, but younger adults may be affected. In contrast, polycythemia due to hemoglobinopathies and congenital cyanotic heart diseases is usually detected in younger patients.

Pathophysiology

The pathophysiology varies according to the cause:

High EPO Levels

Cellular hypoxia can occur due to any cause that triggers the release of erythropoietin from the renal peritubular interstitial fibroblast-like cells. A small amount of EPO is also produced by the liver. Erythropoietin then acts on erythroid progenitor cells, stimulating erythropoiesis. 

Low EPO Levels

The primary defect in nearly 95% of cases of polycythemia vera is an acquired mutation in exon 14 of the Janus kinase 2 (JAK2) gene (V617F). Mutations have also been described in exon 12 of the JAK2 gene. These mutations disrupt the inhibitory regulation of the pseudokinase domain, leading to constitutive signaling. This constitutive activation results in both hypersensitivity to EPO and EPO-independent erythroid colony formation.[5]

Histopathology

Bone marrow examination is part of the World Health Organization (WHO) diagnostic criteria and is recommended in most cases. If the clinical suspicion of polycythemia vera is high despite the absence of a JAK2 (V617F) mutation, or when mutation testing is unavailable, bone marrow examination is especially helpful. Classic findings in combination with other suggestive hematologic parameters help support a diagnosis of polycythemia vera.[6] Strongly suggestive findings include a hypercellular marrow with erythroid hyperplasia and subtle megakaryocytic atypia.[7] Trilineage hyperproliferation is also an expected feature.

History and Physical

History

Common presenting symptoms are frequently nonspecific and may include the following:

• Fatigue, headache, dizziness, transient blurred vision, amaurosis fugax, and other symptoms suggestive of transient ischemic attacks 
• Infrequently, pruritus after a warm-water shower, particularly on the back
• Epistaxis, gastrointestinal tract bleeding, or easy bruising
• Peptic ulcer disease

  • This commonly coexists, and patients may present with nonspecific abdominal pain. Left hypochondrial pain and early satiety should raise the suspicion of splenomegaly.

Rarely, patients may present with unexplained thrombotic complications such as Budd-Chiari syndrome or digital infarcts. A history of smoking, an extended stay at high altitudes, and congenital cardiac disease are important elements of the history. A significant family history may be noted in patients with hemoglobinopathies.

Physical Examination

The physical examination may offer clues to the cause of polycythemia:

• Abnormal facial ruddiness 
• Erythromelalgia may be an atypical presenting feature [8]
• Cyanosis, clubbing, and a heart murmur on auscultation suggest congenital heart disease
• Nicotine staining of the nails and teeth provides presumptive evidence of tobacco use
• Morbid obesity could raise the possibility of obesity hypoventilation syndrome, whereas a barrel chest could suggest obstructive lung disease
• A palpable spleen 
• A renal artery bruit may suggest renal arterial stenosis 

Evaluation

Due to the broad array of potential causes, the evaluation should be sequential and appropriate to the clinical context:

Hemogram

Based on the WHO 2016/2022 criteria, hematocrit levels greater than 49% in men and 48% in women at sea level are suggestive of polycythemia vera. A concurrent increase in platelet and leukocyte counts may be present as well. The leucocyte count is usually between 10,000 and 20,000/µL with eosinophilia and basophilia. Platelet counts may rarely exceed 1,000,000/µL.

Radioisotope Studies

Radioisotope studies using chromium-labeled autologous RBC transfusions accurately determine the RBC mass and conclusively exclude spurious polycythemia; however, red cell mass studies are rarely used in modern practice.

Serum EPO Levels

The presence of either high or low EPO levels directs the next step:

• Low EPO levels:

  • Low EPO levels indicate primary polycythemia. Subsequent evaluation should focus on the detection of polycythemia vera. JAK2 mutation studies are diagnostic for polycythemia vera in 95% of cases. Mutations may occur either in exon 14 (more commonly) or in exon 12.
• High EPO levels:

  • High EPO levels indicate secondary polycythemia. Subsequent evaluation should aim to determine the cause and may include:

    • Measurement of arterial oxygen saturation using a pulse oximeter; low levels indicate a pulmonary or cardiac cause.
  • Normal oxygen saturation levels could require further evaluation, such as:

    • Measurement of carboxyhemoglobin levels in people who smoke tobacco
    • Measurement of the partial pressure of oxygen at which hemoglobin is 50% saturated with oxygen (P₅₀ of hemoglobin) to detect high-affinity hemoglobinopathies
    • Relevant investigations to detect an EPO-secreting tumor

Serum Ferritin, Vitamin B₁₂, and Folate Levels

Low serum ferritin and low folate levels are more strongly associated with primary polycythemia.[3] Strikingly elevated vitamin B₁₂ levels may be observed due to increased transcobalamin III secretion by leukocytes. 

Assessment of Renal Function

Renal function abnormalities are associated with an increased likelihood of secondary polycythemia. Serum uric acid levels are often elevated due to increased cell proliferation and subsequent turnover.

Assessment of Hepatic Function

Hepatocellular carcinoma may cause secondary erythrocytosis via ectopic EPO production.[3]

Ultrasonography

Ultrasonography with a Doppler study of the abdomen can identify a secondary cause. In suspected secondary polycythemia, additional investigations, such as chest radiograph, lung function tests, sleep studies, and echocardiogram, may be indicated.

Treatment / Management

The treatment of secondary polycythemia is directed at the underlying cause. Available treatment modalities include:

Phlebotomy

Phlebotomy has been established as the backbone of therapy, primarily based on the Polycythemia Vera Study Group (PVSG) trial. The study findings showed that, compared with chlorambucil or radioactive phosphorus treatment, phlebotomy alone was associated with longer median survival.[9] The rationale behind repeated phlebotomies was that cytoreduction would reduce hyperviscosity. Additionally, reducing RBC mass would induce iron deficiency, decreasing erythropoiesis.

In practice, weekly sessions are conducted, during which approximately 500 mL of blood is removed, and hemodynamic stability is maintained. This regimen is continued weekly until a target hematocrit of less than 45% is achieved.[10] This target was determined based on findings from the Cytoreductive Therapy in Polycythemia Vera trial (CYTO-PV), in which patients treated at this threshold had significantly lower rates of cardiovascular death and major thrombotic events.[11]

For secondary polycythemias, phlebotomy is usually reserved for the following conditions:[12]

• Chronic lung diseases
• Cyanotic heart diseases
• Posttransplant erythrocytosis after renal transplant in patients with hypertension not responding to optimal doses of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers

Hydroxyurea

Hydroxyurea is usually considered second-line therapy. Results from a PVSG study showed lower rates of thrombosis than in a historical cohort treated with phlebotomy alone.[13] Despite theoretical concerns, the study findings have not demonstrated a significant association between hydroxyurea use and an increased risk of leukemic transformation.[14] Indications include the following:

• Poor venous access
• High phlebotomy requirement
• Phlebotomy is unavailable due to logistical constraints
• Severe thrombocytosis
• Intractable pruritus

The standard daily dose ranges from 500 to 1500 mg. Doses are adjusted to target platelet counts less than 500,000/µL. However, dose adjustment should also maintain the absolute neutrophil count greater than 2000/µL.

Ruxolitinib

The JAK2 inhibitor ruxolitinib is used when patients are intolerant or unresponsive to hydroxyurea. The use of ruxolitinib in myeloproliferative disorders was based on findings in the Controlled Myelofibrosis Study With Oral JAK Inhibitor Treatment  (COMFORT) trials. The COMFORT-I study compared the efficacy of ruxolitinib with placebo therapy, whereas COMFORT-II compared it with the best available therapy. Both trials showed findings of significant reductions in splenomegaly and improvements in symptoms.[14][15] 

Contemporary data from the Integra Precision Q database, which compiled data from over 10,000 patients, showed that nearly 85% of individuals who switched from a standard therapy comparing phlebotomy and hydroxyurea to ruxolitinib achieved a hematocrit less than 45%.[16] Results from cohort studies indicate that patients requiring a therapy switch were more likely to be younger, have fewer comorbidities, and be symptomatic.[17] However, the use of ruxolitinib was associated with increased risks of dose-limiting anemia and thrombocytopenia.

Notwithstanding the clinical benefits, real-world evidence suggests limited adoption.[18] While phlebotomy and hydroxyurea remain the standard first-line therapy, alternatives are often not explored even in individuals experiencing suboptimal clinical responses. Results from one study showed that nearly 87% of patients initiated on phlebotomy monotherapy did not progress to other regimens.[18] The recommended dose for polycythemia vera is 10 mg twice a day. Dose reduction is required if hemoglobin falls below 12 g/dL. If hemoglobin decreases to less than 8 gm/dL, a temporary dosage interruption may be warranted. 

Low-Dose Aspirin

Findings from the original PVSG trial showed that patients treated with phlebotomy alone were at greater risk of thrombosis during the first 3 years of therapy, despite greater longevity, suggesting a potential benefit of concurrent antiplatelet and anticoagulant therapy. However, initial trials using higher doses of aspirin or dipyridamole resulted in gastrointestinal hemorrhage. Results from subsequent studies found that lower doses of aspirin were safe.[19] Currently, low-dose aspirin is recommended for most patients without contraindications, typically at doses of 40 to 100 mg daily.

Hypouricemic Agents

Allopurinol and febuxostat may be required in patients with significant hyperuricemia. Recent study findings indicate that allopurinol may be a safer alternative with respect to all-cause and cardiovascular mortality.[20]

Management of Pruritus

Depending on the severity of pruritus and the response to therapy, therapeutic modalities available for symptomatic relief include antihistamines and selective serotonin reuptake inhibitors.[21][22]

Management of Polycythemia Vera in Pregnancy

The standard therapeutic measures of phlebotomy and low-dose aspirin are appropriate in most patients. Patients at higher risk may require the addition of pegylated interferon-α.[23]

Management of Neonatal Polycythemia

Most neonates do not require treatment; exchange transfusion is occasionally required due to hyperviscosity.

Differential Diagnosis

The differential diagnosis of polycythemia vera includes the following:

• Primary myelofibrosis
• Chronic myeloid leukemia
• Essential thrombocythemia
• Erythropoietin receptor mutations

Prognosis

The median survival of patients diagnosed with polycythemia vera is approximately 14.1 years.[14] Factors associated with a better prognosis include the following:

Pruritus

The association with an improved prognosis is unclear, but could be attributed to:

• Lead-time bias: Patients with significant pruritus were more likely to seek medical attention early
• Lower risk of arterial thrombosis  [24]

Factors associated with worse outcomes included the following:

• Higher leucocyte counts
• Venous thrombosis
• Leukoerythroblastic blood smear: Can be associated with progression to postpolycythemia myelofibrosis

Complications

Secondary polycythemia is associated with complications arising from hyperviscosity and an increased risk of thrombosis. Progression to malignant neoplasms is more characteristic of polycythemia vera and is influenced by prior cytotoxic therapy. Commonly encountered complications include:

• Bleeding: Recurrent epistaxis or gastrointestinal tract bleeding is common and may lead to iron-deficiency anemia, potentially confounding clinical findings, including bone marrow appearance.
• Thrombosis: Hyperviscosity increases the risk of both arterial and venous thrombosis. Arterial thrombosis includes digital infarcts and cerebral ischemic infarcts, particularly in watershed territories. Venous thrombosis, such as Budd-Chiari syndrome, is also frequent.
• Accelerated atherosclerosis: Individuals with polycythemia vera, particularly those with an elevated platelet-to-lymphocyte ratio, may be at an increased risk of accelerated atherosclerosis.[25] This association has been corroborated by findings from other single-center studies demonstrating increased carotid plaque burden over time in individuals without a complete hematologic response to polycythemia vera treatment, compared with those with a complete hematologic response.[26]

Progression to leukemia, particularly acute myeloid leukemia, occurs in approximately 2% to 3% of patients over long-term follow-up and is often refractory to treatment. Prior exposure to chlorambucil, pipobroman, or radioactive phosphorus increases the likelihood of progression.

Consultations

A hematology consultation should be obtained in all cases of suspected primary polycythemia.

Deterrence and Patient Education

Patients must be encouraged to stop smoking. Genetic counseling must be offered to the families of those with hemoglobinopathies. Patients with polycythemia vera must be discouraged from donating blood. Because this is a myeloproliferative disorder, blood from donors with polycythemia vera is not accepted for donation in most countries.

Enhancing Healthcare Team Outcomes

Polycythemia can affect multiple organ systems, and symptoms are primarily due to impaired oxygen delivery and blood hyperviscosity. The condition is primarily managed by the hematologist, but managing complications requires an interprofessional team comprising clinicians, specialists, nursing staff, pharmacists, and phlebotomists. Patients need clinicians to educate them about potential complications and when to seek medical assistance. Pharmacists help manage medication regimens, verify dosing, check for interactions, and offer patients medication counseling. Nurses assist in patient evaluation, counsel patients about their condition, answer patient questions, and serve as coordinators for the activities of the various disciplines covering the case. The interprofessional model requires open communication among all care team members, including accurate record-keeping. This approach will improve patient outcomes.

While survival has improved over the past 3 decades, the aim is also to maintain quality of life. Apart from thrombotic complications, there is also an increased risk of bleeding as well as a risk of infections. Finally, patients should be made aware that they need lifelong follow-up because there is a risk of progression to acute leukemia or myeloproliferative syndrome. Nursing staff should coordinate and monitor close follow-up, assist in educating the patient and family, and ensure regular care is provided.[27] 

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Disclosure: Ashwin Pillai declares no relevant financial relationships with ineligible companies.

Disclosure: Anahat Kaur declares no relevant financial relationships with ineligible companies.

Disclosure: Shiva Kumar Mukkamalla declares no relevant financial relationships with ineligible companies.