Haematological manifestations of systemic disease.

supply oxygen to the tissues, prevent microbial invasion and promote haemostasis. To ensure a sufficient number of cells for these functions, the bone marrow produces 1012 red cells, 1011 leucocytes and 1011 platelets daily to replace those lost through senescence or use. Because of this high rate of proliferative activity, the bone marrow is susceptible to disorders that: • interfere with its anatomical integrity • suppress the production of haematopoietic growth factors • stimulate the production of inflammatory cytokines, or • shorten the lifespan of circulating blood cells. Indeed, systemic diseases frequently first become manifest through either their impairment or stimulation of blood cell production or their enhancement of blood cell destruction or sequestration. Thus, when confronted with an abnormality in haematopoiesis in an adult, it is first necessary to determine whether it is a primary blood disorder or secondary to an underlying systemic disease. This distinction is crucial for the appropriate management of the blood abnormality. When the haematological abnormality is secondary to a systemic disorder, correction of that disorder will alleviate the haematological abnormality, while haematinic therapy alone will not (Fig 1). There is, of course, no correlation between the severity of a blood abnormality and its underlying cause, which must be diligently sought if treatment is to be effective. The evaluation of a blood disorder begins with the medical history, including prior blood counts and assessment of drug or toxin exposure, followed by a careful physical examination with attention to the presence of jaundice, telangiectasia, purpura, lymphadenopathy and splenomegaly. Careful examination of a blood smear is essential as is a reticulocyte count, which can distinguish decreased red cell production from increased red cell destruction unless both are present. A bone marrow biopsy is mandatory when there is pancytopenia or when bone marrow cannot be aspirated, in order to distinguish marrow aplasia from myelofibrosis or metastatic tumour in the bone marrow.