Immature reticulocyte fraction definition
Immature reticulocyte fraction (IRF) is the percentage of the most immature, RNA-rich reticulocytes among all circulating reticulocytes, reported by automated analyzers. [1]
What counts as “high” IRF
A “high” IRF is an IRF value above the laboratory’s provided reference interval, which varies by analyzer, assay method, and patient population. [2]
Typical reference ranges (examples)
Because reference intervals differ by platform and population, “high” should be interpreted using the local lab range.
- Adult example reference interval: 1.6–10.5%. [1]
- Age-specific example (reticulocyte parameter update document; values shown for IRF in %):
- 1 year and greater: 2.8–13.5%
- 14 days to <1 year: 3.6–24.5%
- 0–13 days: 5.5–43.0% [3]
Clinical meaning of a high IRF
A high IRF indicates increased release of younger reticulocytes into circulation, which commonly occurs with heightened erythropoiesis (such as after acute blood loss or hemolysis) and may also be seen with recovery from anemia. [4]
When “high IRF” interpretation requires context
IRF interpretation requires correlation with the complete blood count and reticulocyte production measures because IRF alone does not establish the underlying cause. [4]
Common practical interpretation approach
- Compare the reported IRF to the laboratory reference interval for the patient’s age and the specific analyzer used. [2]
- Correlate IRF elevation with hemoglobin/hematocrit level, absolute reticulocyte count, and RBC indices to determine whether the result fits hemolysis, recovery after treatment, or another pattern. [4]