What are the possible causes of elevated red blood cell count and hematocrit in women?

Causes of Elevated RBC Count and Hematocrit in Women

Elevated RBC count and hematocrit in women (Hgb >16 g/dL or Hct >48%) should prompt evaluation for polycythemia vera first, followed by secondary causes including chronic hypoxia, hereditary hemochromatosis, and less commonly, other myeloproliferative disorders.

Primary Causes

Polycythemia Vera (Most Important to Rule Out)

PV is the critical diagnosis not to miss given its thrombotic risk and need for specific treatment 1. The diagnostic threshold is hemoglobin >16 g/dL or hematocrit >48% in women 2, 1.

Key diagnostic features:

• >95% have JAK2 mutation - this is the single most important test to distinguish primary from secondary causes 1
• Bone marrow shows hypercellularity with trilineage proliferation 2
• Subnormal serum erythropoietin level (minor criterion) 2
• Often accompanied by thrombocytosis (53%) and leukocytosis (49%) 1

Clinical red flags suggesting PV:

• Pruritus (33% of patients), especially after warm baths
• Erythromelalgia (5.3%) - burning pain in extremities
• Splenomegaly (36%) with abdominal discomfort 1
• Prior thrombotic events (16% arterial, 7% venous at diagnosis) 1

Secondary Causes (More Common Overall)

Secondary erythrocytosis is actually more common than PV but carries different implications 3.

Chronic Hypoxia

• Smoking - most common secondary cause
• Sleep apnea
• Chronic lung disease
• High altitude residence
• Cyanotic heart disease

These conditions stimulate erythropoietin production appropriately, leading to increased RBC mass 3, 1.

Hereditary Hemochromatosis

This is an underrecognized cause that presents with erythrocytosis plus elevated hemoglobin 4. Critical distinguishing features:

• Elevated Hb levels despite microcytosis (low MCV) 4
• Normal RDW initially 4
• Most common genetic disorder in Caucasians 4
• Mean corpuscular hemoglobin (MCH) and MCHC are increased due to enhanced iron uptake by erythroid cells 5
• Transferrin saturation ≥75% suggests significant iron overload 5

Common pitfall: Hemochromatosis is often initially mistaken for beta-thalassemia trait when microcytosis is present, but the elevated hemoglobin distinguishes it 4.

Other Secondary Causes

• Renal cell carcinoma or other EPO-secreting tumors
• Testosterone therapy (though less relevant in women unless exogenous use) 6
• Dehydration (relative polycythemia - hemoconcentration)

Diagnostic Algorithm

1. Confirm true erythrocytosis: Repeat CBC, ensure adequate hydration
2. Order JAK2 mutation testing immediately - if positive, strongly suggests PV 1
3. Measure serum erythropoietin level:
   • Low/normal with JAK2+ = PV 2
   • High = secondary cause 3
4. Assess for hypoxia: Pulse oximetry, arterial blood gas, sleep study if indicated
5. Iron studies: Ferritin, transferrin saturation, serum iron
   • Elevated ferritin + high transferrin saturation = consider hemochromatosis 4, 5
   • Consider HFE gene testing (C282Y mutation) 5
6. If JAK2 positive: Bone marrow biopsy to confirm PV diagnosis 2

Critical Clinical Distinctions

Hemochromatosis vs Beta-Thalassemia Trait: Both can present with microcytosis and elevated RBC count, but hemochromatosis has elevated hemoglobin while thalassemia trait has normal or low hemoglobin 4.

PV with iron deficiency: Can present with microcytosis (MCV <70) but maintains elevated RBC count. After iron repletion, MCV normalizes but RBC count remains elevated 7. This combination of microcytic polycythemia should prompt evaluation for both PV and secondary causes with concurrent iron deficiency 7.

Post-iron treatment: In secondary polycythemia with iron deficiency, giving iron causes MCV to normalize but RBC count remains elevated, confirming the underlying polycythemic state 7.