A calculated index from CBC results that helps sort common causes of small red cells.
The red blood cell distribution width index (RDWI) is a calculated value, not a separate blood test. It combines three figures from a full blood count: red cell distribution width (RDW), mean corpuscular volume (MCV) and the red blood cell count (RBC).
The formula is: RDWI = (RDW × MCV) ÷ RBC count (in millions per microlitre).
Iron deficiency anaemia and beta thalassaemia trait both produce small red cells, but they differ in cell size variation and cell number. RDWI uses these differences to help tell the two apart, often performing well compared with other discrimination indices.
A value above 220 suggests iron deficiency anaemia, while a value below 220 suggests beta thalassaemia trait. It is a screening clue, not a diagnosis.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
Interpretive thresholds:
The index is a screening guide only and needs confirmation with iron studies and haemoglobin electrophoresis.
The index can be misleading when iron deficiency and thalassaemia coexist, or in mixed anaemias. It depends on accurate red cell indices, which automated analysers usually provide reliably, but it cannot replace confirmatory testing.
Read with its components, RDW, MCV and red blood cell count, and alongside ferritin, iron studies and haemoglobin electrophoresis.
What does a high or low RDWI mean? Higher values can fit an iron-deficiency pattern. Lower values may fit a thalassemia trait pattern. Always confirm with follow-up tests.
Do I need to fast for this test? No. RDWI uses CBC values, and fasting is not required.
What can affect my RDWI results? Recent transfusion, iron or vitamin therapy, pregnancy, inflammation, dehydration, altitude, and hard workouts can shift CBC values.
How often should I check RDWI? Usually only when anemia is suspected, being treated, or rechecked. Your clinician will guide timing.
How quickly are results ready? Results are usually ready in about 7 days.
What should I discuss with my clinician? Share symptoms, diet, bleeding history, medications, and any transfusions. Ask whether to order iron studies or hemoglobin analysis.
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