Why would a 62-year-old man's hemoglobin and hematocrit increase from normal values to 17.9 g/dL and 53.8 % within one week?

Rapid Hemoglobin/Hematocrit Elevation: Diagnostic Approach

A jump from normal to H/H 17.9/53.8 within one week in a 62-year-old man is almost certainly relative polycythemia (hemoconcentration) rather than true erythrocytosis, because red blood cell production cannot increase this rapidly—even with maximal erythropoietin stimulation, hemoglobin rises only approximately 0.3 g/dL per week. 1

Understanding the Timeline

The temporal pattern is the critical diagnostic clue here:

• True erythrocytosis develops over weeks to months, not days, because erythropoietin-driven red cell production requires time for stem cell differentiation and maturation 1
• Erythropoietin therapy increases hemoglobin by only 0.3 g/dL per week (hematocrit rise of 1% per week), representing the maximum physiologic rate of red cell mass expansion 1
• A 1-week timeframe for this magnitude of change (hemoglobin rising ~3-4 g/dL, hematocrit ~8-10%) is physiologically impossible through increased red cell production alone 1

Most Likely Causes: Plasma Volume Depletion

The rapid rise points to hemoconcentration from plasma volume loss:

Dehydration-Related Causes

• Acute dehydration from inadequate fluid intake, particularly in elderly patients with diminished thirst response 1
• Diuretic use or escalation, which contracts plasma volume while red cell mass remains constant 1
• Gastrointestinal losses from vomiting, diarrhea, or nasogastric suction 1
• Third-spacing in conditions like burns, though this would typically be clinically obvious 1

Stress Polycythemia (Gaisböck Syndrome)

• Chronic plasma volume contraction in hypertensive, obese, or anxious individuals, though this typically develops more gradually 1

Diagnostic Workup Algorithm

Step 1: Confirm the Elevation and Assess Hydration

• Repeat hemoglobin and hematocrit after aggressive hydration with oral or IV fluids—if values normalize, this confirms relative polycythemia 1
• Single measurements are unreliable for establishing true erythrocytosis; serial measurements are mandatory 1
• Assess volume status clinically: orthostatic vital signs, mucous membrane moisture, skin turgor, jugular venous pressure 1

Step 2: Review Medications and Recent Changes

• Diuretic therapy (loop, thiazide, or combination agents) is a common culprit 1
• Testosterone therapy can cause erythrocytosis, but this develops over 3+ months, not 1 week—injectable testosterone causes erythrocytosis in 43.8% of users, but the timeline doesn't fit 2

Step 3: If Values Remain Elevated After Rehydration

Only proceed with extensive workup if hemoglobin/hematocrit remain elevated after confirming adequate hydration:

• Complete blood count with red cell indices, reticulocyte count, and peripheral smear to assess for true erythrocytosis 1
• Serum ferritin and transferrin saturation to evaluate iron status 1
• JAK2 mutation testing (exon 14 V617F and exon 12) if true erythrocytosis is confirmed, as this detects polycythemia vera in up to 97% of cases 1, 3
• Serum erythropoietin level to differentiate primary (low EPO) from secondary (elevated EPO) causes 1, 3

Step 4: Evaluate for Secondary Causes if EPO is Elevated

• Pulse oximetry and arterial blood gas to assess for hypoxemia (target: oxygen saturation <92% suggests secondary polycythemia) 1
• Sleep study if nocturnal hypoxemia from obstructive sleep apnea is suspected 1
• Smoking history and carbon monoxide exposure, as "smoker's polycythemia" causes chronic tissue hypoxia 1
• Renal imaging (ultrasound or CT) to exclude renal cell carcinoma or other erythropoietin-producing tumors 1
• Pulmonary function tests and chest imaging if COPD or other chronic lung disease is suspected 1

Critical Thresholds and Management

When to Intervene

• Therapeutic phlebotomy is indicated ONLY when hemoglobin >20 g/dL AND hematocrit >65% with symptoms of hyperviscosity (headache, dizziness, visual disturbances) after excluding dehydration 1, 3
• This patient's values (17.9/53.8) are well below intervention thresholds 1, 3
• Repeated routine phlebotomies are contraindicated due to risk of iron depletion, decreased oxygen-carrying capacity, and paradoxically increased stroke risk 1

Monitoring Strategy

• If borderline elevated after rehydration, serial measurements every 1-2 months are appropriate until etiology is determined 3
• Hemoglobin is more reliable than hematocrit for monitoring, as hematocrit can falsely increase by 2-4% with prolonged sample storage or hyperglycemia 1

Common Pitfalls to Avoid

• Never diagnose true erythrocytosis based on a single measurement, especially with such a rapid rise—always confirm with repeat testing after addressing hydration 1, 3
• Never perform phlebotomy without first confirming adequate hydration and excluding relative polycythemia, as this worsens hemoconcentration and increases stroke risk 1
• Don't overlook medication review, particularly diuretics, which are easily reversible causes 1
• Don't assume polycythemia vera without JAK2 testing, as secondary causes are far more common and require different management 1, 3

Expected Clinical Course

If this represents relative polycythemia from dehydration:

• Values should normalize within 24-48 hours of adequate fluid repletion 1
• No further workup is needed if hemoglobin/hematocrit return to baseline 1

If values remain elevated despite rehydration:

• Proceed with systematic evaluation for true erythrocytosis as outlined above 1, 3
• Consider hematology referral if JAK2 mutation is positive, hemoglobin >20 g/dL with hyperviscosity symptoms, or diagnosis remains unclear 1