An audit of dynamic function tests: errors in the timing of blood specimens

The interpretation of dynamic endocrine investigations is dependent on the timing of blood sampled after a stimulus. We have studied the accuracy with which doctors adhered to a prescribed protocol.

A new request form for dynamic tests was designed to include both the planned and the actual time of blood sampling in order to allow assessment of the variance of sample timing.

We followed 152 investigation procedures comprising 791 planned specimens. A total number of 627 timing intervals could be analysed of which 366 timing intervals did not differ from the planned interval. Protocols were divided into long and short (greater or less than 6 hours) and into those governed by clock times or 'stopwatch', i.e. minutes elapsed, intervals.

A total of 22% specimens were taken more than 10 minutes earlier or later than planned. Six per cent of specimens were taken more than 30 minutes earlier or later than planned.

The data presented in this study suggest that in order to improve the interpretative accuracy of dynamic tests, it would appear prudent to pay more attention to the accuracy of sample timing. New dynamic test publications should include time tolerance for the normal response.