How good are doctors at estimating children's weight?

OBJECTIVE: (1) To see whether children are weighted before drugs are prescribed in an accident and emergency (A&E) department; (2) to assess how safe it is for doctors to guess children's weight if they prescribe "by eye".
METHODS: An audit of 100 sets of notes was performed to see if children were weighed before drugs were prescribed. A&E senior house officers were asked to estimate the weight of 75 children aged 12 years and under.
RESULTS: Children were weighed before prescribing in only two out of 100 cases. The mean difference between the actual and estimated weights was -0.21 (not significantly different from zero: P = 0.40); 95% of the estimates were within two standard deviations of the mean difference. The percentage difference between the actual and estimated weight varied between overestimates of 300% and underestimates of nearly 100%.
CONCLUSIONS: The average guess of doctors as a group was approximately correct. However, there was a wide range of estimates for individuals. If the child's weight is guessed, the doctor could risk under- or overprescribing analgesia, sedation, or intravenous fluids. Given the wide range of estimates, actual weights are required for accurate prescribing. Prescribing on an age basis may be acceptable for drugs such as paracetamol or amoxycillin, but it is imperative to prescribe on a mg/kg basis for opiates, sedatives, and intravenous fluids because of the large variation in weight that can occur for a single age.