Interpretation of diagnostic mammography varies across facilities; and the failure to adjust for patient characteristics when comparing facility performance could lead to erroneous conclusions, according to a study in the June issue of the Journal of the National Cancer Institute.

Sara L. Jackson, MD, from the department of internal medicine at the University of Washington School of Medicine in Seattle, and colleagues surveyed facilities performing diagnostic mammography within three registries of the Breast Cancer Surveillance Consortium about their structure, organization and interpretive processes. They prospectively assessed performance measurements (false-positive rate, sensitivity and the likelihood of cancer among women referred for biopsy [positive predictive value (PPV2) of biopsy recommendation]) from Jan. 1, 1998 through Dec. 31, 2005.

Researchers reported that 45 of the 53 facilities completed a facility survey (85 percent response rate), and 32 of the 45 facilities performed diagnostic mammography. The analyses included 28,100 diagnostic mammograms performed as an evaluation of a breast problem, and data were available for 118 radiologists who interpreted diagnostic mammograms at the facilities.

Performance measurements demonstrated statistically significant interpretive variability among facilities (sensitivity, P = 006; false-positive rate, P < .001; and PPV2, P < .001) in unadjusted analyses.

However, after an adjustment forpatient and radiologist characteristics, only false-positive rate variation remained statistically significant and facility traits associated with performance measures changed (false-positive rate = 6.5 percent; sensitivity = 73.5 percent; and PPV2 = 33.8 percent), the authors wrote.

Jackson and colleagues noted that facilities reporting that concern about malpractice had moderately or greatly increased diagnostic exam recommendations at their location had a higher false-positive rate and a non-statistically significantly higher sensitivity. Facilities offering specialized interventional services had a non-statistically significantly higher false-positive rate.

Based on their research, the authors said that patient and radiologist characteristics should be considered when comparing the performance of mammography interpretation between facilities.