What is the next step in managing a 44-year-old female with elevated red blood cell (RBC) count, hematocrit (Hct), and platelets while on amlodipine (calcium channel blocker)?

Management of Elevated RBC, Hematocrit, and Platelets in a 44-Year-Old Female on Amlodipine

The next step in managing a 44-year-old female with elevated red blood cell count, hematocrit, and platelets while on amlodipine should be testing for JAK2 mutation to evaluate for polycythemia vera. 1

Initial Diagnostic Approach

• Elevated red blood cell count, hematocrit, and platelets in a middle-aged female strongly suggests polycythemia vera (PV), which is characterized by erythrocytosis (hemoglobin >16.0 mg/dL in women), often accompanied by thrombocytosis (53% of cases) and leukocytosis (49% of cases) 1
• Testing for JAK2 gene variant is essential as it is present in >95% of PV cases and helps distinguish PV from secondary causes of erythrocytosis 1, 2
• Serum erythropoietin (EPO) level should be measured simultaneously, as low levels support a diagnosis of PV while elevated levels suggest secondary polycythemia 2

Clinical Significance and Risk Assessment

• PV significantly increases risk of both arterial thrombosis (16% of patients) and venous thrombotic events (7% of patients), which can involve unusual sites such as splanchnic veins 1
• Patients with PV also have increased bleeding risk, especially with extreme thrombocytosis (platelet count ≥1000 × 10^9/L) due to acquired von Willebrand disease 1
• Current use of amlodipine (calcium channel blocker) is not contraindicated in this setting, as dihydropyridine calcium channel blockers like amlodipine are generally well-tolerated in patients with various hematologic conditions 3

Management Algorithm

1. Confirm diagnosis of PV:

   • JAK2 mutation testing
   • Serum erythropoietin level
   • Rule out secondary causes (sleep apnea, smoking, hypoxic conditions) 1, 2

2. If PV is confirmed:

   • Initiate therapeutic phlebotomy with a goal hematocrit of <45% 1, 4
   • Start low-dose aspirin (80-100 mg daily) if no contraindications exist 1, 4
   • Assess thrombotic risk factors (age ≥60 years, history of thrombosis) 1

3. For high-risk PV patients (age ≥60 years or prior thrombosis):

   • Add cytoreductive therapy with hydroxyurea or interferon to lower thrombosis risk 1
   • Continue therapeutic phlebotomy and aspirin 4

4. Blood pressure management:

   • Continue amlodipine if blood pressure is well-controlled 3
   • If blood pressure is elevated, optimize antihypertensive therapy according to guidelines 3
   • For patients with resistant hypertension, consider screening for primary aldosteronism 3

Important Considerations

• Amlodipine can be safely continued in this patient as dihydropyridine calcium channel blockers have neutral effects on morbidity and mortality in various conditions 3
• Avoid non-dihydropyridine calcium channel blockers (verapamil, diltiazem) if heart failure develops, as they have negative inotropic effects 3
• Monitor for symptoms of hyperviscosity including headache, visual disturbances, and erythromelalgia 1
• Long-term monitoring is necessary as PV can progress to myelofibrosis (12.7% of patients) or acute myeloid leukemia (6.8% of patients) 1

Pitfalls to Avoid

• Do not attribute elevated blood counts solely to medication effects; amlodipine overdose typically causes hypotension rather than polycythemia 5, 6
• Avoid delaying diagnosis and treatment of PV, as thrombotic events are often the initial manifestation of the disease and can be fatal 2
• Do not use hydroxyurea in women of childbearing potential without appropriate contraception due to teratogenic risk 4
• Avoid excessive phlebotomy that might lead to iron deficiency, which can worsen thrombocytosis 4

By following this approach, you can properly diagnose and manage this patient's elevated blood counts while maintaining appropriate antihypertensive therapy.