What would be found in the peripheral blood smear of a patient with a high immature reticulocyte (reticulocyte count) fraction and medium fluorescence reticulocyte fraction, and a normal thrombocyte (platelet) count?

Peripheral Blood Smear Findings in High Immature Reticulocyte Fraction with Normal Platelet Count

In a patient with elevated immature reticulocyte fraction (IRF) and medium fluorescence reticulocytes with normal platelet count, the peripheral blood smear would most likely show polychromasia (blue-gray reticulocytes), anisocytosis, and potentially nucleated red blood cells, indicating active bone marrow erythropoietic response to anemia or hemolysis. 1

Expected Reticulocyte Morphology

• Polychromatic red blood cells (reticulocytes) appear as larger, blue-gray cells on Wright-Giemsa stain due to residual RNA content, which is the hallmark finding when IRF is elevated 1, 2
• The presence of medium fluorescence reticulocytes (18.7 ± 5.1% in normal individuals) indicates moderately immature reticulocytes with intermediate RNA content 2
• High IRF (≥0.23 or 23%) reflects increased release of younger reticulocytes from bone marrow, suggesting active erythropoiesis in response to anemia, hemolysis, or blood loss 1

Additional Red Cell Findings

• Anisocytosis (variation in red cell size) is commonly present due to the mixture of mature erythrocytes and larger, younger reticulocytes 3
• Nucleated red blood cells (nRBCs) may appear in the peripheral smear when bone marrow stress is severe, particularly in conditions like hemolytic anemia or myelofibrosis 3
• The absence of nRBCs would be expected in complete remission states of myeloproliferative disorders 3

Clinical Context Interpretation

When IRF is Elevated (≥0.23):

• Hemolytic anemia: Expect polychromasia, spherocytes (if hereditary spherocytosis), sickle cells (if sickle cell disease), or fragmented cells (if microangiopathic hemolysis) 4, 1
• Acute blood loss: Polychromasia with otherwise normal red cell morphology initially 5, 1
• Recovery from bone marrow suppression: Polychromasia with improving cell counts after chemotherapy or nutritional repletion 1, 6

Differential Diagnosis Based on Smear:

• Normal platelet count excludes primary bone marrow failure syndromes like aplastic anemia or advanced myelodysplastic syndrome, which typically show thrombocytopenia 3
• Absence of dysplastic features (hypogranular platelets, pseudo-Pelger-Huët cells) makes MDS less likely 3
• Presence of specific abnormalities guides diagnosis: spherocytes suggest hereditary spherocytosis, schistocytes suggest microangiopathic hemolysis, target cells suggest hemoglobinopathy 4

Key Diagnostic Pitfalls

• An elevated IRF with normal absolute reticulocyte count may occur in early bone marrow recovery or mild hemolysis, where the bone marrow is releasing younger cells but total production remains limited 1
• IRF <0.23 with anemia indicates inadequate bone marrow response and would show minimal polychromasia, suggesting chronic renal failure, iron deficiency, or bone marrow suppression 1
• The combination of high IRF with medium fluorescence reticulocytes (rather than high fluorescence) suggests moderate rather than maximal erythropoietic stress 2, 7

Normal Platelet Morphology Expected

• With normal platelet count, the smear should show normal platelet size and distribution without giant platelets or platelet clumping 8
• Absence of immature (reticulated) platelets on routine smear, as these require special staining (thiazole orange) for detection and are not visible on standard Wright-Giemsa stain 6, 8