Polycythemia, or erythrocytosis, refers to an increase in the absolute red blood cell (RBC) mass in the body. In practice, this is reflected by an increase in hemoglobin levels, or hematocrit, over what is considered physiologic for that age and gender.
The standard RBC mass does not usually exceed 36 ml/kg in males and 32 ml/kg in females. The reference ranges for normal hemoglobin levels, and hematocrits, vary depending on altitude, from ethnicity to ethnicity, and country to country. However, as a frame of reference, the hemoglobin and hematocrit of a healthy adult male are 16% plus or minus 2 gm/dl and 47% plus or minus 6%, respectively. The hemoglobin and hematocrit of a menstruating adult female are usually 13% plus or minus 2 gm/dl and 40 plus or minus 6%, respectively.
Polycythemia vera is a sub-type of polycythemia. Often referred to colloquially as simply “ polycythemia,” it is an acquired, Philadelphia-chromosome negative,, myeloproliferative disorder. This condition is associated with overproduction of all 3 cell lines, but with a notable prominence of red blood cells.
The clinical significance of erythrocytosis, due to any cause, lies in the associated risk of thrombotic events due to hyperviscosity of blood. Additionally, the potential for progression to leukemia in cases of polycythemia vera also warrants attention.
This occurs due to volume contraction rather than an increase in true RBC mass.
- Severe dehydration due to isolated fluid loss: potentially seen in diarrhea and severe vomiting
- Gaisbock syndrome: Usually seen amongst obese, hypertensive males. Consumption of cigarettes, excessive alcohol, and use of diuretics are contributory.
Further stratified based on serum erythropoietin (EPO) levels as follows:
Low serum EPO levels (Primary polycythemia)
- Polycythemia vera
- Primary familial and congenital polycythemia
High serum EPO levels (Secondary polycythemia)
- High altitude
- Respiratory disorders: Chronic obstructive pulmonary disease (COPD), Pickwickian syndrome
- Cyanotic heart diseases with right-to-left shunts
- Renal disorders: Renal cysts, cancer, renal artery stenosis, Bartter syndrome, focal sclerosing glomerulonephritis
- Elevated carboxyhemoglobin: usually seen in smokers
- Hemoglobinopathies: High-affinity hemoglobins such as Hb Yakima, methemoglobinemia
- EPO-secreting tumors: sources include hepatomas, uterine leiomyomas, and cerebellar hemangiomas
- Iatrogenic causes: Including erythropoietin administration, anabolic steroids, and testosterone replacement therapy
The prevalence of polycythaemia vera has been estimated to be approximately 22 cases per 100,000 population. It is believed to occur more frequently among Jews of Eastern European descent than other Europeans and Asians. Polycythemia vera shows a male preponderance in all races and ethnicities, with a male to female ratio of approximately 2:1. The median age of presentation of PV is 60 years, with patients seldom seen before the age of 40. Polycythemia due to hemoglobinopathies and congenital cyanotic heart diseases is likely to be detected in significantly younger patients.
The pathophysiology would vary, depending on the cause in consideration.
High EPO Levels
Cellular hypoxia can occur due to any cause triggers the release of erythropoietin from the renal peritubular lining capillary cells. A small amount of EPO is produced by the liver as well. EPO, in turn, acts on erythroid progenitor cells and stimulates erythropoiesis.
Low EPO Levels
The primary defect in nearly 95% of cases of polycythemia vera is an acquired mutation in exon 14 of the tyrosine kinase JAK2 (V617F). Mutations have also been described in exon 12 of JAK2. These mutations result in a loss of the auto-inhibitory pseudo-kinase domain of JAK2, resulting in its constitutive activation. This constitutive activation results in both hypersensitivity to EPO and EPO-independent erythroid colony formation.
Bone marrow examination is not routinely employed. Its utility largely remains restricted to cases where the clinical suspicion of polycythemia vera is high, despite the absence of a JAK2 (V617F) mutation, or if facilities to test for the mutation are unavailable. Classical findings, when coexistent with other suggestive hematologic parameters, help support a diagnosis of polycythemia vera.
Strongly suggestive findings include a hypercellular marrow with erythroid hyperplasia and subtle megakaryocytic atypia. Tri-lineage hyperproliferation is also an expected feature.
History and Physical
Common presenting symptoms, usually non-specific, include fatigue, headache, dizziness, transient blurring of vision, amaurosis fugax and other symptoms suggestive of transient ischemic attacks (TIAs).
Infrequently, patients may complain of pruritus after a warm water shower, particularly over the back.
A history of epistaxis, gastrointestinal (GI) bleed or easy bruising may be forthcoming.
Peptic ulcer disease commonly co-exists, and patients may present with non-specific abdominal pain. Left, hypochondrial pain and early satiety should arouse the suspicion of splenomegaly.
Rarely, patients may present with a history of unexplained thrombotic complications, such as Budd-Chiari syndrome or digital infarcts.
It is vital to try and elicit etiology-specific history such as a history of smoking, an extended stay at high altitudes, congenital cardiac disease, among others. A significant family history may be elicited in patients with hemoglobinopathies.
Abnormal facial ruddiness may be prominent.
Cyanosis and clubbing, along with the presence of a murmur on auscultation, provide strong evidence favoring a congenital cyanotic heart disease.
Nicotine staining of the nails and teeth provide presumptive evidence of smoking, even in a non-forthcoming patient.
The presence of morbid obesity could raise the possibility of Pickwickian syndrome; whereas, a barrel chest could suggest an obstructive lung disease.
Examination of the abdomen may lead to finding a palpable spleen or eliciting the bruit of renal arterial stenosis.
An evaluation must proceed sequentially. Due to the broad array of potential causes, it is vital to consider the appropriate investigation in that specific clinical context. However, the following may provide a frame of reference:
Based on the WHO 2017 criteria, hematocrit levels above 49% in males and 48% in females, at sea level, are to be considered suggestive of polycythemia vera. In cases of polycythemia vera, there could be a concurrent increase in platelet and leucocyte counts as well. The leucocyte count is usually between 10,000 to 20,000/microliter and may show eosinophilia and basophilia. Platelet counts may rarely exceed 100,000/microliter.
Radioisotope studies using Cr-labeled autologous RBC transfusions accurately determine the true RBC mass and conclusively exclude spurious polycythemia.
Serum EPO Levels
The presence of either high or low EPO levels directs the further plan of evaluation.
Low EPO levels indicate primary polycythemia. Subsequent evaluation should be targeted toward the detection of polycythemia vera.
JAK2 mutation studies are virtually diagnostic for polycythemia vera (95% cases). Mutations may occur either in exon 14 (more commonly) or in exon 12.
High EPO levels indicate secondary polycythemia. Subsequent evaluation should be aimed at determining the cause. This should include, but not be limited to, the following:
- Measurement of arterial oxygen saturation levels using a pulse-oximeter: low levels would likely indicate a pulmonary or cardiac cause.
- Normal saturation levels could require further evaluation such as:
- The use of a co-oximeter to rule out methemoglobinemia
- Measurement of carboxyhemoglobin levels (for smokers)
- Measurement the P50 of Hb to detect high-affinity hemoglobinopathies
- Relevant investigations to detect a possible EPO-secreting tumor
Serum Ferritin, Vitamin B12, and Folate Levels
Low serum ferritin and low folate levels have been associated more with primary polycythemia. Raised vitamin B12 levels, often striking, may be observed. This occurs due to increased transcobalamin III secretion by leucocytes.
Assessment of Renal Function
Renal function abnormalities indicate a higher likelihood of secondary polycythemia. Uric acid levels are often raised, due to increased cell proliferation and subsequent turnover.
Assessment of Hepatic Status
Liver cirrhosis and inflammatory liver disease have been associated with secondary polycythemia and increased RBC proliferation.
An ultrasound and Doppler study of the abdomen would help identify a secondary cause.
In cases of suspected secondary polycythemia, the utility of additional investigations such as a chest radiograph, lung function tests, sleep studies, and an echocardiograph are to be considered as appropriate.
- Primary myelofibrosis
- Chronic myeloid leukemia
Studies estimate the median survival in cases diagnosed with polycythemia vera to be approximately 14.1 years.
Factors that were found to correlate with better prognosis included:
- Pruritus: The reason for the correlation of pruritus with better prognosis was unclear. This could be attributed to the following:
- Lead-time bias: patients with significant pruritus were likely to seek medical attention earlier.
- Lower risk of arterial thrombosis
Factors associated with worse outcomes included:
- Higher leucocyte counts
- Venous thrombosis
- Leucoerythroblastic blood smear
Secondary polycythemia is associated primarily with complications arising from hyperviscosity. Polycythemia vera is associated with progression to malignant conditions.
Commonly encountered complications include:
- Bleeding: Recurrent epistaxis or GI bleed are often seen, that may lead to iron deficiency anemia, potentially confounding clinical findings, including bone marrow appearance.
- Thrombosis: Due to hyperviscosity, there is a preponderance of both arterial and venous thrombosis. Manifestations of arterial thrombosis include digital infarcts, cerebral ischemic infarcts, particularly in watershed territories. Venous thrombosis such as Budd-Chiari syndrome is also seen.
Progression to leukemia, particularly acute myeloid leukemia (AML) is seen in approximately 5% of cases and is often refractory to treatment. Studies have implicated the use of chlorambucil, pipobroman, or radioactive phosphorous as factors that increase the likelihood of progression.
A hematologist consultation should be sought 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 considered appropriate for donation in most countries.
Enhancing Healthcare Team Outcomes
Polycythemia can affect every organ in the body, and the symptoms are primarily related to impaired oxygen delivery and hyperviscosity of blood. The condition is primarily managed by the hematologist, but the management of complications requires an interprofessional team. Patients need to be educated by the nursing staff and clinicians about the potential complications and when to seek medical assistance. While survival has been improved over the past three decades, the aim is to also improve the quality of life. Two threats to life include bleeding and infection complications. Most patients require red cell transfusions to help improve fatigue. Finally, patients should be told by team members that they need lifelong follow up as there is a risk of progression to acute leukemia or a myelodysplastic syndrome. The nursing staff should coordinate and monitor close followup and assist in educating the patient and family to make sure regular care is obtained. (Level V)