Under physiological conditions, late juvenile red blood cells should not be present in the peripheral blood, and once they are present in the peripheral blood, it may be in a pathological state. The condition that leads to an increase in late juvenile erythrocytes may be a major blood loss, where the patient loses more than 1500 mL of blood and the body is too late to release mature erythrocytes, releasing immature erythrocytes into the peripheral blood. It may also be a pathological condition, where there is a disruption of the barrier between the bone marrow and the blood, such as myelofibrosis and myelodysplastic syndrome. It could also be cancer, where the bone marrow infiltrates and disrupts the barrier between the bone marrow and peripheral blood, and young red blood cells from the bone marrow run into the peripheral blood. Therefore, once the presence of late juvenile red blood cells in the peripheral blood is detected, it must be a pathological condition that requires sufficient attention and should be promptly seen in a hematology clinic for appropriate tests, such as bone marrow aspiration, bone marrow biopsy, bone marrow immunophenotyping, and even chromosomal and genetic tests.