What are the implications of a hemoglobin level of 17.9?

Elevated Hemoglobin at 17.9 g/dL

A hemoglobin level of 17.9 g/dL is elevated above typical reference ranges but may be physiologically normal in certain contexts, requiring systematic evaluation to distinguish between primary erythrocytosis (polycythemia vera), secondary causes (hypoxia, smoking, sleep apnea), and relative erythrocytosis (plasma volume contraction). 1

Clinical Context and Normal Ranges

• At sea level, the 95th percentile for adult males reaches approximately 16.7-17.0 g/dL, meaning 17.9 g/dL exceeds normal population values 1
• However, in high-altitude residents (4000m), normal hemoglobin ranges extend to 21 g/dL in men, with values above this threshold considered abnormal 2
• The standard anemia threshold of <13.5 g/dL in males implies normal values extend above this, but 17.9 g/dL represents true erythrocytosis requiring investigation 1

Diagnostic Approach

Distinguish true erythrocytosis from relative erythrocytosis first:

• Measure total hemoglobin mass and plasma volume, as hemoglobin concentration alone can be misleading 3
• In heart failure and chronic liver disease patients, plasma volume expansion (not hemoglobin deficiency) explains up to 80% of variance in hemoglobin concentration, with identical total hemoglobin masses producing vastly different measured concentrations 3
• This measurement is now simple, cheap, and safe, preventing inappropriate interventions targeting non-existent "hemoglobin deficiency" 3

Evaluate for secondary causes systematically:

• Hypoxia-related: Sleep apnea, chronic lung disease, high-altitude residence, smoking (59% of young adults with erythrocytosis were smokers) 4
• Lifestyle factors: Obesity (43% of young erythrocytosis patients), alcohol excess, dehydration 4
• Medications/substances: Testosterone, erythropoietin-stimulating agents, anabolic steroids

Screen for polycythemia vera:

• JAK2 V617F mutation testing is essential—detected in 10.9% of patients referred for elevated hemoglobin 5
• JAK2 exon 12 mutations account for rare JAK2 V617F-negative cases 5
• Serum erythropoietin level (low in primary, elevated in secondary causes)
• Additional mutations (TET2, DNMT3A, ASXL1) occur in 34.5% of JAK2-positive patients and affect prognosis 5

Common Pitfalls

Avoid these diagnostic errors:

• Failure to follow up: Less than half of young adults with erythrocytosis receive long-term monitoring 4
• Inadequate testing: Only 17.9% had JAK2 mutation testing and 23.2% had serum EPO measured in one cohort, representing discordant management with current recommendations 4
• Missing BCR/ABL1: Three patients with elevated hemoglobin and erythrocytosis were ultimately diagnosed with chronic myeloid leukemia 5
• Assuming hemoglobin deficiency: In conditions with plasma volume expansion (heart failure, liver disease), normal or elevated total hemoglobin mass can present as "anemia" due to dilution 3

Clinical Implications

For asymptomatic patients with 17.9 g/dL:

• No immediate intervention required if secondary causes identified and managed
• In COPD with chronic respiratory failure, higher hemoglobin levels (above 14.3 g/dL in females, 15.1 g/dL in males) independently predict better long-term survival 6
• Polycythemic COPD patients show higher survival rates than normocythemic patients (P=0.043) 6

If polycythemia vera confirmed:

• Aspirin therapy for thrombosis prevention
• Phlebotomy to maintain hematocrit <45% in men, <42% in women
• Cytoreductive therapy (hydroxyurea) for high-risk patients
• Monitor for additional mutations (ASXL1) that worsen prognosis 5

Management priorities:

• Address modifiable secondary causes: smoking cessation, weight loss if obese, CPAP for sleep apnea
• Relative erythrocytosis from dehydration requires volume repletion, not phlebotomy
• Establish definitive diagnosis before initiating phlebotomy or cytoreductive therapy to avoid treating physiologic adaptation (high altitude, chronic hypoxia) as pathologic 2, 4