RBC morphology can be initially evaluated using automated blood cell analyzers. RBC parameters include the RBC count, hemoglobin, hematocrit, and RBC indices.
RBC indices are calculated RBC parameters.* RBC indices have two main uses:
- They assist with the differentiation of anemias.
- They serve as quality control checks.
RBC indices include:
- Mean cell (or corpuscular) volume (MCV)
- Mean cell hemoglobin (MCH)
- Mean cell hemoglobin concentration (MCHC)
Each of these parameters reflects a characteristic of the red blood cell population that is circulating at the time the blood sample was collected.
MCV refers to the average size of the RBCs constituting the sample. MCV is reported as femtoliters (fL). One femtoliter is 10-15 L. Reference interval for adults is typically 80–100 fL. On some hematology instrumentation, flags for macrocytosis and microcytosis may be generated due to the patient's MCV falling outside of the reference range.
Mean cell hemoglobin (MCH) refers to the average weight of hemoglobin in the RBCs. MCH is reported as picograms (pg). One picogram is 10 -12 grams. The reference interval for adults is typically 26–32 pg.
Mean cell hemoglobin concentration (MCHC) refers to the average concentration of hemoglobin in the RBCs. MCHC is reported as g/dL. The reference interval for adults is typically 32–36 g/dL. Instrument flags such as hypochromasia or hyperchromasia may be generated when the MCHC is outside the reference range.
The red cell distribution width (RDW) is a measurement derived from the red blood cell distribution curves generated on automated hematology analyzers and is an indicator of variation in RBC size within a blood sample. The instrument flag 'anisocytosis' may be generated when the RDW is higher than the reference range (11.5–14.5%). The RDW is used along with the indices (MCV, MCH, MCHC) to describe a population of RBCs.
When abnormalities are noted, further evaluation may be necessary to confirm RBC morphology.
*Some hematology instruments measure MCV directly and derive hematocrit, rather than calculating MCV from a measured hematocrit and red blood cell count.
