Elevated RBC Count with Decreased MCHC: Diagnostic Implications
An elevated red blood cell (RBC) count with decreased mean corpuscular hemoglobin concentration (MCHC) most commonly indicates iron deficiency with compensatory erythrocytosis, which requires further evaluation for underlying causes such as chronic hypoxia, polycythemia vera with iron deficiency, or other conditions affecting iron metabolism.
Understanding the Laboratory Parameters
- RBC count refers to the total number of red blood cells per volume of blood, with elevated values suggesting increased erythropoiesis 1
- MCHC represents the average concentration of hemoglobin in a given volume of packed red blood cells, with decreased values indicating reduced hemoglobin content within each cell 1
- This combination creates a distinctive pattern where there are more red blood cells than normal, but each cell contains less hemoglobin than it should 1
Common Causes of Elevated RBC with Decreased MCHC
Iron Deficiency with Secondary Polycythemia
- Iron deficiency leads to decreased hemoglobin synthesis (causing low MCHC), while an underlying condition stimulates increased RBC production 2
- Secondary polycythemia from chronic hypoxia (such as in chronic lung disease, congenital heart disease, or high altitude) with concurrent iron deficiency is a classic cause of this pattern 1
- The body attempts to compensate for hypoxia by increasing RBC production, but without sufficient iron, these cells become microcytic with reduced hemoglobin concentration 1
Polycythemia Vera with Iron Deficiency
- Polycythemia vera (PV) patients who develop iron deficiency (often from phlebotomy treatments or occult bleeding) can present with elevated RBC count and decreased MCHC 2
- In PV with iron deficiency, the bone marrow continues to produce excessive RBCs despite inadequate iron stores 1
- These patients typically have low serum erythropoietin levels, which helps distinguish them from those with secondary polycythemia 1
Thalassemia Trait
- Thalassemia minor (trait) can present with elevated RBC count and decreased MCHC 2
- Unlike iron deficiency, RBC distribution width (RDW) is typically normal in thalassemia trait 2
- Family history and hemoglobin electrophoresis can help confirm this diagnosis 1
Diagnostic Approach
- Evaluate iron studies (serum iron, total iron binding capacity, ferritin) to assess iron status 1
- Check reticulocyte count to determine if there is active erythropoiesis 1
- Consider serum erythropoietin level, which is typically low in polycythemia vera but elevated in secondary polycythemia 1
- Assess for hypoxemia through oxygen saturation or arterial blood gas analysis 1
- Screen for occult bleeding with stool guaiac testing if iron deficiency is confirmed 1
- Consider bone marrow examination in cases where the diagnosis remains unclear 1
Clinical Implications and Management
- Iron deficiency in patients with elevated RBC counts should prompt investigation for the underlying cause of both the iron deficiency and the erythrocytosis 1
- In secondary polycythemia with iron deficiency, iron supplementation may increase hemoglobin concentration while RBC count remains elevated 2
- In polycythemia vera with iron deficiency, addressing the underlying myeloproliferative disorder is essential before correcting iron deficiency 1
- Monitoring both RBC count and MCHC during treatment helps assess response and guide management 1
Important Considerations and Pitfalls
- Laboratory errors can cause spurious results - verify abnormal findings before extensive workup 3
- Hyperglycemia can affect RBC indices, potentially causing falsely elevated MCV and altered MCHC 4
- Chronic inflammatory states may mask iron deficiency by falsely elevating serum ferritin 1
- Soluble transferrin receptor (sTfR) levels may help identify iron-deficient erythropoiesis when traditional iron studies are equivocal 5
- Patients with cyanotic congenital heart disease commonly develop this pattern due to chronic hypoxia with secondary iron deficiency 1