Management of Elevated Hematocrit with Low MCHC
Your patient's hematocrit of 46.8% with MCHC of 32.1 g/dL requires immediate evaluation for iron deficiency in the setting of possible erythrocytosis, as this combination suggests iron-deficient red blood cells that compromise oxygen transport and increase stroke risk. 1, 2
Initial Diagnostic Approach
Confirm True Erythrocytosis
- Repeat the complete blood count to verify the elevated hematocrit, as a single measurement may not be reliable 2
- Check if this represents true polycythemia versus relative polycythemia from dehydration 2
- The hematocrit of 46.8% is borderline elevated (normal for males is 47 ± 6%, for females 41 ± 5%) 2
Evaluate the Low MCHC
- The MCHC of 32.1 g/dL is below normal range (normal 32-36 g/dL) and strongly suggests iron deficiency 1, 2
- This combination of elevated hematocrit with low MCHC is particularly concerning in erythrocytosis, as iron deficiency causes reduced hemoglobin without proportional change in hematocrit, compromising oxygen transport without lowering viscosity 1
- Mean corpuscular volume (MCV) is unreliable for screening iron deficiency in erythrocytosis—you must check serum iron, ferritin, and transferrin saturation 1, 2
Essential Laboratory Workup
Order the following tests immediately: 2
- Complete blood count with red cell indices and reticulocyte count
- Serum ferritin and transferrin saturation
- Peripheral blood smear review
- C-reactive protein (CRP)
- JAK2 mutation testing (exon 14 and exon 12) if true erythrocytosis is confirmed 2
Critical Pitfall to Avoid
High RDW with normal or low MCV suggests iron deficiency coexisting with erythrocytosis 2. The low MCHC in your patient already indicates this, but examining the RDW will provide additional confirmation.
Management Based on Iron Status
If Iron Deficiency is Confirmed (Transferrin Saturation <20%)
Iron deficiency in erythrocytosis is a medical emergency requiring treatment 1:
- Iron-deficient red blood cells have reduced oxygen-carrying capacity and deformability, increasing stroke and myocardial ischemia risk 1
- Initiate cautious oral iron supplementation with close hemoglobin monitoring, as rapid increases in red cell mass can occur 2, 3
- Symptoms of iron deficiency mimic hyperviscosity symptoms 1
Avoid Routine Phlebotomy
Do not perform phlebotomy unless specific criteria are met 1, 2, 3:
- Phlebotomy is indicated ONLY if hemoglobin >20 g/dL AND hematocrit >65% with hyperviscosity symptoms 1, 2, 3
- Repeated routine phlebotomies are contraindicated due to risk of iron depletion, decreased oxygen-carrying capacity, and stroke 1, 2, 3
- If phlebotomy is necessary, replace with equal volume of dextrose or saline 2
Rule Out Secondary Causes
Evaluate for common secondary causes of erythrocytosis: 2
- Smoking history (causes "smoker's polycythemia" from carbon monoxide exposure) 2
- Obstructive sleep apnea (nocturnal hypoxemia drives erythropoietin production) 2
- COPD or other pulmonary disease 2
- Testosterone use (prescribed or unprescribed) 2
- Cyanotic congenital heart disease 1, 2
- Renal dysfunction 2
If Polycythemia Vera is Diagnosed
For confirmed PV (requires JAK2 mutation plus elevated hemoglobin/hematocrit): 1, 2, 3
- Maintain hematocrit strictly <45% through phlebotomy (target may be 42% for women) 1, 3
- Low-dose aspirin 81-100 mg daily unless contraindicated 1, 3
- Risk stratify: high-risk (age ≥60 or thrombosis history) requires cytoreductive therapy with hydroxyurea 1, 3
- First address iron deficiency before aggressive phlebotomy 1
Immediate Next Steps
- Rehydrate the patient (oral or IV fluids) as first-line therapy before any other intervention 1
- Order iron studies immediately (ferritin, transferrin saturation, serum iron) 1, 2
- Check JAK2 mutations if true erythrocytosis is confirmed 2
- Treat iron deficiency if present, even in the context of elevated hematocrit 1, 2
- Monitor hemoglobin closely during iron supplementation 2