What is the red cell distribution width (RDW) for a 54‑year‑old man with microcytic, hypochromic anemia given hemoglobin 118 g/L, hematocrit 0.39, mean corpuscular volume 73 fL, mean corpuscular hemoglobin 22 pg, and mean corpuscular hemoglobin concentration 306 g/L?

RDW Cannot Be Calculated from the Provided Values

Red cell distribution width (RDW) is a direct measurement by automated hematology analyzers and cannot be calculated from hemoglobin, hematocrit, MCV, MCH, or MCHC values. 1

Understanding RDW as a Laboratory Parameter

• RDW is an automated laboratory determination of red cell anisocytosis (variation in red blood cell size) that is measured directly by the analyzer, not derived from other indices 2
• The normal reference range for RDW is typically 11.5-14.5%, with a mean value around 11.3% in healthy individuals 3
• RDW reflects the coefficient of variation of red blood cell volume distribution and requires direct measurement of individual cell volumes by the analyzer 2

Clinical Context: Your Patient Has Microcytic Hypochromic Anemia

Based on the provided values (MCV 73 fL, MCH 22 pg, MCHC 306 g/L), this patient demonstrates:

• Microcytic anemia (MCV < 80 fL) with hypochromia (MCH < 27 pg, MCHC < 320 g/L), most commonly caused by iron deficiency and requiring immediate iron studies including serum ferritin and transferrin saturation 4, 5
• The combination of low MCH and low MCHC strongly suggests iron deficiency anemia, though thalassemia trait must be excluded 4, 6

Why RDW Would Be Clinically Important Here

• In iron deficiency anemia, RDW is typically elevated (>14.5%) with sensitivity of 67.9% for detecting IDA, reflecting increased variation in red cell size as the body produces progressively smaller cells 2
• In thalassemia trait, RDW may be normal or only mildly elevated despite microcytosis, helping differentiate it from iron deficiency 6, 7
• RDW is proportional to reticulocyte count and reflects active erythropoiesis, with higher values indicating more active red cell production 3

Next Steps for This Patient

• Order a complete iron panel immediately (serum ferritin, transferrin saturation, serum iron, TIBC) to confirm iron deficiency, with ferritin <30 μg/L confirming the diagnosis in the absence of inflammation 1, 4
• Request the actual RDW value from the laboratory as it should be included in the standard CBC report and is essential for differentiating iron deficiency from thalassemia trait 6, 2
• If iron studies confirm deficiency, initiate ferrous sulfate 325 mg (65 mg elemental iron) 1-3 times daily between meals and investigate the underlying cause of iron loss 4