(HealthDay News) — Thyroid ultrasound imaging can be used to identify patients at low risk of thyroid cancer, according to a study published in the Aug. 26 issue of JAMA Internal Medicine.

Rebecca Smith-Bindman, M.D., from the University of California in San Francisco, and colleagues conducted a retrospective case-control study involving 8,806 patients who underwent 11,618 thyroid ultrasound examinations from Jan. 1, 2000, through March 30, 2005. Data were linked with the California Cancer Registry to identify thyroid cancers.

The researchers identified 105 patients diagnosed with thyroid cancer. Thyroid nodules were common among patients diagnosed with and without cancer (96.9% and 56.4%, respectively). The only ultrasound nodule characteristics associated with the risk of thyroid cancer were microcalcifications (odds ratio [OR], 8.1), size greater than 2 cm (OR, 3.6), and an entirely solid composition (OR, 4.0).

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Most cases of thyroid cancer would be detected if one characteristic were used as an indication for biopsy (sensitivity, 0.88), with a high false-positive rate (0.44) and low positive likelihood ratio (2.0); 56 biopsies would be performed per cancer diagnosed. With a two-characteristic requirement for biopsy, the sensitivity would be lower (0.52), false-positive rate lower (0.07), and positive likelihood ratio higher (7.1); 16 biopsies would be performed per cancer diagnosed. Adoption of this rule rather than performing biopsies on all nodules larger than 5 mm would reduce unnecessary biopsies by 90%, while keeping a low risk of cancer.

“Thyroid ultrasound imaging could be used to identify patients who have a low risk of cancer for whom biopsy could be deferred,” the authors write.