What does elevated hemoglobin and hematocrit indicate?

Elevated Hemoglobin and Hematocrit in a 61-Year-Old Female

The elevated red blood cell count (5.51), hemoglobin (18.8), hematocrit (54.8), and MCV (99.5) in a 61-year-old female strongly indicate polycythemia that requires immediate evaluation for underlying causes, particularly polycythemia vera, which can significantly increase risk of thrombotic events and mortality if left untreated. 1

Interpretation of Laboratory Values

Your laboratory values show:

• RBC: 5.51 (elevated)
• Hemoglobin: 18.8 g/dL (significantly elevated)
• Hematocrit: 54.8% (significantly elevated)
• MCV: 99.5 fL (high normal/slightly elevated)
• MCHC: 34.1 g/dL (normal)

These values demonstrate erythrocytosis (increased red blood cell mass), which is defined as a hematocrit >48% in women according to current guidelines 1. The elevated MCV suggests a macrocytic tendency, which can be seen in certain forms of polycythemia.

Diagnostic Algorithm

Step 1: Determine if this is absolute or relative polycythemia

• Your hematocrit of 54.8% exceeds the threshold for absolute polycythemia in women (>48%) 1
• The combination of elevated hemoglobin, hematocrit, and RBC count strongly suggests absolute polycythemia rather than relative polycythemia (which would be due to plasma volume depletion) 2

Step 2: Differentiate between primary and secondary polycythemia

Primary causes:

• Polycythemia vera (PV) - a myeloproliferative neoplasm

Secondary causes:

• Hypoxia-driven: Chronic lung disease, sleep apnea, high altitude, smoking
• Non-hypoxia driven: Tumors producing erythropoietin, kidney disease, exogenous testosterone or androgen use 1

Step 3: Recommended diagnostic workup

1. Serum erythropoietin (EPO) level - Low in PV, normal/elevated in secondary causes 1
2. JAK2 V617F mutation testing - Present in >95% of PV cases 1
3. JAK2 exon 12 testing - If JAK2 V617F is negative but PV still suspected 1
4. Oxygen saturation and arterial blood gas - To assess for hypoxic causes
5. Abdominal ultrasound - To check for splenomegaly (common in PV) 2

Important Clinical Considerations

Potential Causes to Consider

1. Polycythemia vera - A primary bone marrow disorder that should be strongly suspected given your significantly elevated values 1
2. Exogenous testosterone or androgen use - Can cause significant erythrocytosis in women 3, 4
3. Chronic hypoxic conditions - Such as undiagnosed sleep apnea or COPD 1
4. Smoking - The most common cause of secondary polycythemia 2
5. Kidney disease or renal tumors - Can cause inappropriate EPO production 1

Risk Implications

• Thrombotic events - Elevated hematocrit increases blood viscosity and significantly raises risk of stroke, myocardial infarction, and venous thromboembolism 1
• Hyperviscosity symptoms - Headache, dizziness, visual disturbances, and fatigue may occur 1

Management Considerations

If polycythemia vera is confirmed:

• Therapeutic phlebotomy to maintain hematocrit <45% (or appropriate level for women) 1
• Low-dose aspirin (81-100 mg daily) to reduce thrombotic risk 1
• Cytoreductive therapy (hydroxyurea or interferon-alfa) for high-risk patients 1

If secondary polycythemia is identified:

• Treatment of the underlying cause
• Phlebotomy may still be needed to reduce thrombotic risk 4

Common Pitfalls to Avoid

• Overlooking secondary causes - Comprehensive evaluation is necessary before concluding PV diagnosis 5
• Assuming blood donation alone is sufficient - Studies show that blood donation may not adequately control hematocrit in patients with persistent erythrocytosis 4
• Delaying diagnosis - These significantly elevated values warrant prompt evaluation due to increased thrombotic risk 1

The macrocytosis (elevated MCV) in your case adds another dimension requiring investigation, as it may suggest vitamin B12 or folate deficiency, liver disease, or could be related to a myeloproliferative disorder itself 1.