Objective: To investigate whether mean platelet volume may be a useful rapid indicator of the presence of 22q11.2 deletion.

Method:
Design and setting: Retrospective analysis of mean platelet volume and 22q11.2 deletion status in a paediatric population undergoing cardiac surgery at the Royal Brompton Hospital, between August 1999 and June 2005. Genetic testing was performed in 166 children (< 16 years).
Main outcome measures: 22q11.2 deletion status and mean platelet volume. A mean platelet volume of >10fL was considered abnormal.

Results: Twenty one children were 22q11 positive. The mean platelet volume was significantly larger 10.9fL for the 22q11.2 positive patient group compared to 8.6fL in the non-22q11.2 patients (p <0.001). Platelet counts were significantly lower in the 22q11.2 patient group (median 155x109/L v 225x109/L, p=0.008). The area under the curve of the receiver operating characteristics curve of mean platelet volume was large enough (0.85) to enable the accurate prediction of 22q11.2 deletion using mean platelet volume.

Conclusion: Mean platelet volume >10 fL is a positive predictor of the presence of 22q11.2 deletion in children with congenital heart disease. This finding should aid rapid decision-making for ordering irradiated blood products to prevent potentially fatal transfusion-associated graft versus host disease and to alert clinicians to monitor serum calcium levels closely to prevent hypocalcaemic seizures.