Diagnosis and Management of Elevated Hemoglobin and Hematocrit

Initial Evaluation

The American College of Physicians recommends verifying that hemoglobin/hematocrit exceeds the 95th percentile for sex and race, or document an increase above the patient's individual baseline regardless of absolute values 2
Evaluate for dehydration immediately: assess for dry mucous membranes, decreased skin turgor, orthostatic hypotension, review fluid intake/losses, and consider fasting status 3
Ensure adequate hydration and repeat CBC within 1-2 weeks to determine if values normalize, as a single measurement may mask the true clinical picture 4, 3
Obtain serial measurements every 4 hours if acute illness is present, since initial normal values can mask evolving pathology 4, 5

Look specifically for thrombocytosis (platelet count >400 × 10⁹/L), leukocytosis (WBC >10 × 10⁹/L), microcytosis from iron deficiency, splenomegaly on examination, aquagenic pruritus (itching after water exposure), unusual thrombosis including Budd-Chiari syndrome, and erythromelalgia (burning pain in extremities) 2, 5
Low serum EPO (specificity >90%) is highly suggestive of polycythemia vera but not diagnostic, as it can occur in other myeloproliferative disorders 2, 3
Normal serum EPO does not exclude PV (sensitivity <70%), so PV remains a consideration 2
Elevated serum EPO strongly suggests secondary erythrocytosis from hypoxemia (chronic lung disease, congenital heart disease, sleep apnea, high altitude) or other causes 2, 1

The American Society of Hematology recommends maintaining hematocrit strictly below 45% to reduce cardiovascular death and major thrombotic events from 9.8% to 2.7% (hazard ratio 3.91) 1
Prescribe low-dose aspirin 100 mg daily for all PV patients unless contraindicated to significantly reduce thrombotic events 1
High-risk patients (requiring cytoreductive therapy) include those with age ≥60 years, history of prior thrombosis, poor phlebotomy tolerance, symptomatic or progressive splenomegaly, platelet count >1,500 × 10⁹/L, and leukocyte count >15 × 10⁹/L 1, 5

Do NOT perform routine phlebotomy in secondary erythrocytosis, as it causes iron deficiency, decreases oxygen-carrying capacity, and paradoxically increases stroke risk 1
Phlebotomy is indicated ONLY when hematocrit >65% (hemoglobin >20 g/dL), symptoms of hyperviscosity are present, patient is adequately hydrated, and no iron deficiency is present (transferrin saturation >20%) 1, 5
Evaluate iron status using serum iron, ferritin, and transferrin saturation, and treat iron deficiency with iron supplementation until stores are replete, monitoring hemoglobin closely 1, 5

Hydration is first-line therapy—NOT phlebotomy—for suspected hyperviscosity symptoms, and phlebotomy should only be considered after confirming no iron deficiency 1, 5
In plasma leakage syndromes (Dengue, Capillary Leak), do NOT transfuse or phlebotomize based on elevated hematocrit during active plasma leakage, and begin aggressive crystalloid resuscitation through large-bore IV access 5
Low MCHC with normal MCV suggests early iron deficiency before microcytosis develops, and iron deficiency should be treated first before considering any phlebotomy 3, 1