Pancytopenia

Pancytopenia is the simultaneous reduction of red blood cells, white blood cells, and platelets. It is a finding, not a diagnosis. The clinical risk comes from the cell line that is failing most severely: reduced red-cell mass limits oxygen delivery, neutropenia weakens host defence, and thrombocytopenia impairs primary haemostasis. The mechanism matters because the same low counts can arise from very different problems. The marrow may be producing too few cells, abnormal cells may be replacing normal marrow, or cells may be destroyed or sequestered after leaving the marrow. Aplastic anaemia is the classic production-failure pattern. Autoreactive cytotoxic T cells and inflammatory cytokines injure haematopoietic stem and progenitor cells, so the marrow loses its ability to replenish all three blood-cell lines. The result is a markedly hypocellular marrow with fatty replacement rather than a marrow crowded by blasts or fibrosis. Because neutrophils, platelets, and red cells are all reduced, infection, bleeding, and symptomatic anaemia can develop together. Severe aplastic anaemia is defined by marrow cellularity below 25% plus at least two of these findings: - absolute neutrophil count (ANC) below...