Approach to a Child with Low Red Cell Distribution Width (RDW) and Mean Platelet Volume (MPV)

Understanding RDW and MPV Values

The Centers for Disease Control and Prevention recommends that RDW is calculated by dividing the standard deviation of red blood cell volume by MCV and multiplying by 100 to express as a percentage 1
Normal RDW is generally ≤14.0%, corresponding to the 95th percentile in reference populations 3
Low RDW indicates a homogeneous red cell population with minimal variation in cell size 3

The Centers for Disease Control and Prevention suggests checking MCV to determine if microcytosis is present 1, 2
If low MCV and normal/low RDW (≤14.0%) are present, thalassemia minor is the most likely diagnosis 1, 2, 3
Confirm hemoglobin levels to determine presence and severity of anemia 4

Avoid unnecessary iron supplementation, which is ineffective in thalassemia and may cause iron overload 3
Monitor for concurrent conditions as thalassemia carriers can develop iron deficiency 3

Age-appropriate reference ranges should be used as MCV is highest at birth, decreases during the first 6 months, then gradually increases during childhood 1

Don't assume all microcytic anemias are due to iron deficiency; low RDW with low MCV strongly suggests thalassemia minor 1
Laboratory values can vary between different instruments, so interpret according to the specific laboratory's reference range 3
Don't overlook the possibility of combined disorders (e.g., thalassemia with concurrent iron deficiency) 3
Avoid empiric iron therapy without proper diagnosis, as it's ineffective in thalassemia and may cause harm 3