From the Guidelines
Initial lab testing for persistent polycythemia should include a complete blood count (CBC) with differential, erythropoietin level, and measurement of arterial hemoglobin-oxygen saturation and carboxyhemoglobin level, especially in smokers. This approach is based on the most recent and highest quality evidence available, which emphasizes the importance of distinguishing between primary and secondary causes of polycythemia 1.
Key Components of Initial Lab Testing
- Complete blood count (CBC) with differential to assess hematocrit levels and rule out other blood disorders
- Erythropoietin level to determine if the polycythemia is primary or secondary
- Measurement of arterial hemoglobin-oxygen saturation and carboxyhemoglobin level to evaluate oxygen saturation and rule out central hypoxic states
- Additional tests such as serum ferritin, abdominal ultrasound, and bone marrow aspiration and biopsy may be necessary if initial tests are inconclusive
Rationale for Testing
The rationale for this approach is to distinguish between primary polycythemia (polycythemia vera) and secondary causes, as management strategies differ significantly between the two 1. Primary polycythemia is characterized by low erythropoietin levels and often positive JAK2 mutation, while secondary polycythemia typically presents with normal or elevated erythropoietin levels and negative JAK2 mutation. Early diagnosis is crucial to guide appropriate management and prevent complications.
Considerations for Secondary Causes
Specific testing for secondary causes should be guided by clinical suspicion and may include sleep studies for obstructive sleep apnea, pulmonary function tests for chronic lung disease, or renal imaging for kidney tumors that might produce erythropoietin 1.
From the Research
Initial Lab Testing for Persistent Polycythemia
- Initial lab testing for persistent polycythemia typically involves a combination of tests, including:
- Complete Blood Count (CBC) to evaluate red blood cell count, hemoglobin, and hematocrit levels
- Erythropoietin (EPO) level to assess for low EPO, which is a minor criterion for Polycythaemia Vera (PV) 2, 3, 4
- JAK2 V617F mutation test to detect the presence of this mutation, which is a major criterion for PV 2, 3, 5, 4
- Red Cell Mass (RCM) measurement to confirm the presence of true polycythemia 4
- The diagnostic performance of EPO levels and JAK2 V617F mutation has been evaluated in several studies, with results showing that JAK2 V617F mutation is a more sensitive and specific marker for PV than EPO level 2, 3, 4
- A low EPO level (< 2 mIU/mL) has been shown to be highly specific for PV, but has low sensitivity 2
- The combination of haematocrit, JAK2 V617F mutation, and EPO level can improve the diagnostic accuracy for PV 3, 4