Differential Diagnosis for Normal CBC with Elevated RDW

Single Most Likely Diagnosis

• Iron deficiency anemia: This is the most common cause of an elevated RDW (Red Cell Distribution Width) with a normal CBC (Complete Blood Count). Iron deficiency leads to a variation in red blood cell size, resulting in an increased RDW. Even if the CBC appears normal, early iron deficiency can cause an increase in RDW before other parameters like hemoglobin or hematocrit become abnormal.

Other Likely Diagnoses

• Vitamin B12 or folate deficiency: Deficiencies in these vitamins can lead to ineffective erythropoiesis, resulting in a mix of normal and large red blood cells, thus elevating the RDW. These deficiencies might not immediately result in anemia or changes in other CBC parameters.
• Chronic disease: Chronic diseases, such as chronic kidney disease or liver disease, can lead to a mixed anemia picture with an elevated RDW due to the body's inability to effectively utilize iron or produce erythropoietin.
• Mixed anemia: A combination of microcytic and macrocytic anemias can result in a normal hemoglobin and hematocrit but an elevated RDW due to the variation in red blood cell size.

Do Not Miss Diagnoses

• Myelodysplastic syndrome (MDS): Although less common, MDS can present with a normal CBC but an elevated RDW. It's crucial to consider this diagnosis, especially in older adults, as MDS can progress to acute leukemia and has significant implications for patient management and prognosis.
• Early myeloproliferative neoplasm: Some myeloproliferative neoplasms, like essential thrombocythemia or polycythemia vera in their early stages, might not significantly alter the CBC parameters but could result in an elevated RDW due to abnormalities in red blood cell production.

Rare Diagnoses

• Sideroblastic anemia: A rare disorder characterized by the presence of ringed sideroblasts in the bone marrow, which can lead to a mixed anemia picture with an elevated RDW.
• Paroxysmal nocturnal hemoglobinuria (PNH): A rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells, which might present with an elevated RDW among other more specific findings.
• Inherited disorders affecting red blood cell production: Such as congenital dyserythropoietic anemias, which are rare and can present with an elevated RDW due to abnormalities in red blood cell morphology and production.