The patient has a normocytic anaemia. There is also a mild leucocytosis due to a neutrophilia, a mild thrombocytosis and an elevated ESR.

The cause of the anaemia in this situation may be complex and multifactorial. The anaemia of chronic disease is the most likely cause. This is an extremely common cause for anaemia, with only iron deficiency being more common. It is a poorly understood condition often found in chronic inflammatory disorders such as rheumatoid arthritis, malignancy or chronic infection. It is characterised by a low serum iron in the presence of adequate iron stores. The pathogenesis is complex, involving a mild shortening of red cell survival, an inappropriately low production of erythropoietin for the degree of anaemia, impaired marrow response to erythropoietin and abnormal iron metabolism.

However, patients with the anaemia of chronic disease may also have co-existent causes of anaemia and the laboratory abnormalities considered classic of other causes may not be present. Iron deficiency may be due to gastrointestinal blood loss related to gastric erosions or ulceration. Folate deficiency may be related to poor diet and difficulty with manipulating eating utensils due to the joint deformity. The presence of the anaemia of chronic disease or co-existent iron deficiency may mask the macrocytosis that is usually seen with vitamin B₁₂ or folate deficiency. Haemolytic anaemia may also occur in autoimmune diseases and should be excluded.

It would be appropriate to order iron studies and serum vitamin B₁₂ and red cell folate assays. As discussed in Case 3, in complex situations like this, iron studies may not give a clear indication of the presence of iron deficiency and a bone marrow assessment of iron stores will then be required. A direct anti-globulin (Coomb's) test will determine if there is any immunoglobulin coating the red cells. If positive, it raises the possibility of an auto-immune haemolytic anaemia. However, it is possible to have a positive anti-globulin test in the absence of haemolysis. Tests to exclude other diseases associated with anaemia are also indicated (serum creatinine, liver function tests, thyroid function tests).

In John's case the vitamin B₁₂ and red cell folate levels were normal. Iron studies showed a low serum iron and low serum transferrin, consistent with the findings in patients with the anaemia of chronic disease. The serum ferritin was elevated at 380 , reflecting the role of ferritin as an acute phase reactant. The Coomb's test was negative. Renal and liver function tests were normal. The final diagnosis was therefore the anaemia of chronic disease.

The primary treatment is that of the underlying condition. The anaemia is rarely severe enough to be of clinical importance, although it is wise to monitor the haemoglobin level. Some patients may have symptoms that justify transfusion (e.g. developing angina at a particular haemoglobin level). Erythropoietin is effective in many cases but is expensive and not funded for this indication in Australia.