Parents have been using ear thermometers incorrectly and getting falsely reassuring information about their children's health.

The government issued a safety warning about their use yesterday in the light of six reports of children needing urgent hospital treatment after mistaken home readings.

Four involved children being treated for leukaemia or a blood disorder and two involved children who suffered febrile convulsions because of a virus.

The warning to GPs and other health professionals to ensure that parents know how to use the thermometers comes six months after researchers at Liverpool University warned that their use could prove unreliable and inconsistent.

The infrared aural thermometer has become more widely used by parents, especially those monitoring children with long-term diseases, because getting a conventional thermometer under the tongue can be difficult.

Temperatures over 37C (98.6C) can be an early indication of fever. The government's medical and healthcare products regulatory agency said yesterday that investigations suggested that users were not keeping the lens showing the temperature clean, or were using the instrument improperly.

It should be properly aimed at the eardrum to calculate the patient's temperature.

Incorrect placing might mean thermometers responded to the heat in the ear canal, which could give readings 2C lower.

Sometimes a firm but gentle pull on the ear might be needed to straighten the canal and allow a snug fit. James Meikle