Objectives In 2018 clinicians provided diagnostic imaging tests to almost half of all patients who present to a NSW ED with low back pain. It is unclear how many of these tests were unnecessary. We aimed to determine whether a system to estimate unnecessary imaging rates could be developed and validated in NSW Hospital EDs.

Method Two clinician researchers will screen the clinical charts of people who presented to a NSW ED for low back pain over a one month period. The researchers will read the clinical notes, reason for imaging request, ED discharge letter, ED imaging report, and hospital admission report to judge appropriateness. Using a checklist of guideline indications for urgent imaging, researchers will code each imaging order as being ‘appropriate,’ ‘potentially appropriate’ ‘unnecessary,’ or ‘unable to determine appropriateness.’ To determine reliability of the coding system we will calculate agreement (Kappa).To detect a kappa >=0.6 with 90% power, two raters will review a minimum 255 clinical charts each. This estimate assumes a two-tailed test with a null value of kappa=0.4, proportion of positive ratings =0.3 (ie we expect ∼30% lumbar imaging tests will be rated as ‘appropriate’).

Results Results will be presented at the conference.

Conclusions This study will be the first to estimate the rate of unnecessary diagnostic imaging for low back pain in NSW EDs based on comprehensive case note reviews.