From the Guidelines
When elevated red cell distribution width (RDW) is found, the minimum workup should include red blood cell indices, reticulocyte count, differential blood cell count, serum ferritin, transferrin saturation, and CRP concentration, as recommended by the most recent guidelines 1. To determine the underlying cause of an elevated RDW, several follow-up laboratory tests should be ordered.
- A complete blood count with peripheral smear to assess for anemia and morphological abnormalities of red blood cells
- Iron studies including serum iron, total iron binding capacity, ferritin, and transferrin saturation to evaluate for iron deficiency, as suggested by the espen micronutrient guideline 1
- Vitamin B12 and folate levels to check for deficiencies that can affect red blood cell production
- Reticulocyte count to assess bone marrow response
- Hemoglobin electrophoresis to screen for hemoglobinopathies like thalassemia
- Liver function tests and kidney function tests as organ dysfunction can affect red blood cell production
- Inflammatory markers such as C-reactive protein or erythrocyte sedimentation rate
- Thyroid function tests as thyroid disorders can impact red blood cell production An elevated RDW indicates increased variation in red blood cell size (anisocytosis) and is often an early indicator of nutritional deficiencies, hemoglobinopathies, or other conditions affecting erythropoiesis before other hematologic parameters become abnormal, as noted in the european consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases 1. The specific pattern of abnormalities across these tests helps narrow down the differential diagnosis and guide appropriate treatment, with the most recent and highest quality study recommending a combination of tests including plasma iron, transferrin, transferrin saturation, ferritin, CRP, hepcidin, and evaluation of red blood cell morphology 1.
From the Research
Labs to Check with Elevated RDW
Elevated Red Cell Distribution Width (RDW) can be an indicator of various underlying conditions, including iron deficiency anemia and anemia of chronic disease. The following labs can be checked to further investigate the cause of elevated RDW:
- Complete Blood Count (CBC) to assess hemoglobin, hematocrit, and erythrocyte counts 2
- Reticulocyte count to evaluate bone marrow activity and response to anemia 3
- Serum iron studies, including transferrin and ferritin, to assess iron stores and differentiate between iron deficiency anemia and anemia of chronic disease 3, 4
- Reticulocyte hemoglobin (Ret Hb) to diagnose iron deficiency anemia with high accuracy 3
- Percentage microcytic RBCs (%Micro R) to differentiate between iron deficiency anemia and anemia of chronic disease, although it may be inferior to other parameters 3
- Erythropoietin level to assess the body's response to anemia and underlying disease severity 2
- Hepcidin level to understand the regulation of iron metabolism and its role in anemia of chronic disease 2
- Folic acid and vitamin B12 levels to rule out deficiencies and assess the need for supplementation 2
- Creatinine level to evaluate kidney function and its potential impact on anemia 2
Differential Diagnosis
Differential diagnosis of anemia of chronic diseases is primarily based on the exclusion of other types of anemia, particularly iron deficiency anemia 2. The main features of anemia of chronic diseases include:
- Mild to moderate lowering of hemoglobin level
- Decreased percentage of reticulocyte count
- Low iron and transferrin concentration
- Increased ferritin level
- Presence of underlying chronic disease, such as chronic inflammation, autoimmune diseases, cancer, or kidney failure 2