Paediatric Haematology and Oncology
This domain tests blood count interpretation against age-specific norms, the distinction between immune thrombocytopenia and leukaemia, and the first 24 hours of febrile neutropenia and tumour lysis syndrome.
Normal values and anaemia
Haemoglobin falls physiologically to a nadir around 8-10 weeks, then rises. Iron deficiency anaemia is microcytic with low ferritin and raised soluble transferrin receptor; treat with oral iron and always look for the cause, particularly in older children. Thalassaemia trait shows microcytosis with a normal ferritin and a normal or raised red cell count.
Thrombocytopenia and bleeding
Immune thrombocytopenia: isolated low platelets in a well child with petechiae, often after a viral illness. Blood film is mandatory to exclude blasts. Treatment (intravenous immunoglobulin or steroids) is reserved for significant mucosal bleeding; platelet transfusion is only for life-threatening haemorrhage. Haemophilia A presents in boys with haemarthrosis, prolonged activated partial thromboplastin time and low factor VIII.
Oncology
Acute lymphoblastic leukaemia: pallor, bruising, bone pain, hepatosplenomegaly, lymphadenopathy and blasts on the film. Refer urgently for bone marrow examination. Febrile neutropenia (neutrophils below 0.5 x 10^9/L and fever) needs blood cultures and empirical antipseudomonal beta-lactam antibiotics within one hour. Tumour lysis syndrome: hyperkalaemia, hyperphosphataemia, hypocalcaemia, hyperuricaemia and acute kidney injury; treat with vigorous hydration, allopurinol or rasburicase and close monitoring.
Supports and transfusion
Transfuse red cells for symptomatic anaemia, and platelets below 10 x 10^9/L in stable oncology patients. Irradiated or leucodepleted products are used in defined settings. Newborn haemorrhagic disease is prevented by vitamin K.
Worked example
A 3-year-old is well, with petechiae on the legs, platelets 8 x 10^9/L, normal haemoglobin and white cells, and no organomegaly. The film shows no blasts. This is immune thrombocytopenia. Observe and advise on bleeding precautions; do not give steroids before a film has excluded leukaemia, and do not transfuse platelets simply to raise the count.
Traps
Giving steroids before the blood film; platelet transfusion for a high but asymptomatic count; treating iron deficiency without finding the cause; missing neutropenia in a febrile child on chemotherapy; forgetting rasburicase in high-risk tumour lysis.