Patterns of ordering diagnostic tests for patients with acute low back pain. The North Carolina Back Pain Project

Low back pain is a common reason for visiting a physician. Authors of guidelines and insurance payers are currently scrutinizing use of radiography and computed tomography (CT) or magnetic resonance imaging (MRI).

To study the determinants of the use of lumbar spine radiography and either CT or MRI in patients with acute low back pain.

Prospective cohort study.

Community-based practices in North Carolina in six strata: urban primary care physicians, rural primary care physicians, urban chiropractors, rural chiropractors, orthopedic surgeons, and practitioners at a group-model health maintenance organization.

1580 patients with acute low back pain.

Telephone interviews done after the index office visit and at 2, 4, 8, 12, and 24 weeks or until complete recovery; survey of practitioners; and chart abstraction.

During the acute back pain episode, 46% of patients had radiography and 9% had CT or MRI. Patient variables related to use of radiography included pain that began more than 2 weeks before the index visit and no previous episodes of low back pain. Practitioner variables associated with use of radiography were being a chiropractor or orthopedic surgeon and having a solo practice. Use of CT or MRI was associated with white race, neurologic deficit at baseline, sciatica, poor functional status at baseline, and small group-practice size. Practitioners' responses to clinical vignettes were associated with aggregate practitioner behavior: In the vignettes and in real life, practitioners were more likely to order CT for patients with sciatica. However, a practitioner's response to a vignette did not predict that practitioner's use of CT or MRI for similar patients in his or her own practice.

Radiography is commonly used as a diagnostic test for patients with acute back pain. Clinical factors and provider specialty are major correlates of the use of imaging studies.