Aims Audit all children receiving haematopoietic stem cell transplantation, to look at number with biochemical indices suggestive of laboratory tumour lysis syndrome.

Methods Retrospective analysis of computerised blood results from day −7 to +7 of conditioning, of all 35 paediatric patients undergoing transplantation over three consecutive years from 2006. Sodium, potassium, urea, creatinine, phosphate, magnesium, calcium and leucocyte cell counts were recorded in addition to reason for transplantation. All children received allopurinol from day −10 to +7. Uric acid was not measured.

Results Reasons for transplantation: 17β-thalassaemia major, 8 sickle cell disease, 4 aplastic anaemia, 3 chronic myeloid leukaemia, and 1 for each of juvenile myelomonocytic leukaemia, Glanzman's thrombasthaenia and haemophagocytic lymphohistiocytosis. 453 blood results were recorded, 23 were missing, of these 4 were potassium, 9 calcium and 10 phosphate. 33 patients had a raised phosphate, with 223 measurements greater than 1.5 mmol/l (maximum 3.81 mmol/l). No recorded measurements of potassium greater than 6 mmol/l. One patient had a calcium level of 1.63 mmol/l, with a phosphate of 1.64 mmol/l on day 7, although the hypocalcaemia subsequently resolved permanently, and the hyperphosphataemia had normalised within 24 h. This was the only patient that fitted the laboratory criteria for tumour lysis syndrome, excluding uric acid levels. 34 children (97%) had total white cell count below 0.5×109/l by day 4 post transplantation, but one child's count did not fall below 1 during the 15 day period studied.

Conclusion Although 94% of the children had raised phosphate, only one of the children (2.8%) met the criteria for laboratory tumour lysis syndrome for less than 24 h on day 7 pretransplantation and resolved spontaneously. This child received busulfan from days 9 to -6 inclusive and alemtuzumab from days 8 to 6 inclusive, at a time when risk of tumour lysis syndrome was increased. A consensus on the length of duration of treatment with allopurinol has yet to be reached. From these data we suggest that duration of treatment with allopurinol could be decreased from 7 days post transplantation to 4 for fully myeloablative conditioning regimens.