Approach to a Child with Low Red Cell Distribution Width (RDW) and Mean Platelet Volume (MPV)
When a child presents with low RDW and MPV values, thalassemia minor should be strongly suspected, particularly if microcytosis (low MCV) is also present. 1
Understanding RDW and MPV Values
- 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 2
- Low RDW indicates a homogeneous red cell population with minimal variation in cell size 2
- Low MPV suggests smaller than normal platelets, which can occur in certain inflammatory conditions 3
Diagnostic Algorithm for Low RDW and MPV
Step 1: Evaluate Complete Blood Count
- Check MCV to determine if microcytosis is present 1
- If low MCV and normal/low RDW (≤14.0%) are present, thalassemia minor is the most likely diagnosis 1, 2
- Confirm hemoglobin levels to determine presence and severity of anemia 1
Step 2: Differentiate from Iron Deficiency
- Iron deficiency anemia typically presents with low MCV and high RDW (>14.0%) 1, 4
- Thalassemia minor presents with low MCV but normal or only mildly elevated RDW 2, 4
- This differentiation is crucial as treatment approaches differ significantly 4
Step 3: Additional Testing
- Hemoglobin electrophoresis should be performed to confirm thalassemia and determine specific type 4
- Serum ferritin and transferrin saturation to rule out concurrent iron deficiency 2
- Family history assessment for thalassemia traits 4
Clinical Implications and Management
- Low RDW with low MCV is highly specific for thalassemia minor, with better discrimination than other indices 4
- Patients with thalassemia minor generally do not require specific treatment but need genetic counseling 4
- Avoid unnecessary iron supplementation, which is ineffective in thalassemia and may cause iron overload 2
- Monitor for concurrent conditions as thalassemia carriers can develop iron deficiency 2
Special Considerations in Children
- 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
- In pediatric patients, RDW may be a more reliable indicator than other red cell indices for differentiating thalassemia from iron deficiency 4, 5
- Low MPV in children may be associated with inflammatory conditions and should be evaluated in clinical context 6, 3
Common Pitfalls to Avoid
- Don't assume all microcytic anemias are due to iron deficiency; low RDW with low MCV strongly suggests thalassemia minor 1, 4
- Laboratory values can vary between different instruments, so interpret according to the specific laboratory's reference range 2, 5
- Don't overlook the possibility of combined disorders (e.g., thalassemia with concurrent iron deficiency) 2
- Avoid empiric iron therapy without proper diagnosis, as it's ineffective in thalassemia and may cause harm 2