Increased breast density (defined as radiopaque areas on a mammogram from heterogeneously or extremely dense breast tissue) is identified in about half of women undergoing digital mammography screening exams.1 Increased breast density is a risk factor for breast cancer and can mask breast cancer.2 From 2009 to 2019, 36 states enacted laws to require information on increased breast density in mammography reports.3 The National Health Interview Survey (NHIS)4 included a question about dense breast notification only in 2015.


We used the 2015 NHIS Cancer Control Supplement4 public-use data set to estimate the prevalence of breast density notification and additional tests following mammography. The NHIS is a cross-sectional, in-person survey of a nationally representative sample of the civilian, noninstitutionalized U.S. population, with a multistage cluster sample design. The final sample adult response rate in 2015 was 55.2%. Our study included 5701 women aged 35–74 years who had no prior breast cancer diagnosis, who reported a mammogram as part of a routine exam and not because of a problem within the past 2 years, and who were not missing information about breast density and additional testing.

We identified dense breast notification after a woman’s most recent mammogram with the question: “Were you informed that your mammogram showed that you have dense breast tissue?” Additional tests were identified with: “After your MOST RECENT mammogram, were you advised to have more tests?” and, if yes, “What tests did you actually have?” (none, ultrasound, breast magnetic resonance imaging, additional mammogram(s), biopsy, other).

We used SAS-callable SUDAAN version 11.0 software and NHIS-provided final weights for adult sampling probabilities and nonresponse. We used logistic regression to calculate model-adjusted risk ratios derived from predicted marginals for whether a woman was informed about dense breast tissue by factors such as health status, sociodemographics, and census region.


Overall, 24.9% of our sample reported they were informed that their mammogram showed dense breast tissue (Table 1). Model-adjusted risk ratios for notification were lower than the reference group for women who were aged > 55 years, were black or Hispanic, had not had a mammogram in the past year, were born outside the USA, were not a college graduate, or had income < 250% of the federal poverty threshold (Table 1). Risk ratios were higher than the reference group for women in the Northeast and those with a first-degree family history of breast cancer.

Table 1 Prevalence and Model-Adjusted Risk Ratios of Notification That a Recent Mammogram Showed Dense Breast Tissue, Among Women Aged 35–74 Years, National Health Interview Survey, 2015

Of the group of women informed about dense breast tissue, 26.2% reported additional tests following mammography, with ultrasound (14.6%) being the most common additional test (data about additional tests is not shown in table). Of women not informed about dense breast tissue, only 3.4% reported additional tests.


One in four women in 2015 in all states reported being notified of dense breast tissue following a recent mammogram. This proportion is half of what would be expected if notifications had been required nationwide in 2015.1 Women with less education, lower income, black or Hispanic heritage, or age group 55–74 years and those who were immigrants were less likely to report dense breast notification.

Ultrasound was the additional test most commonly reported following mammography by women with dense breast notification. Whether the ultrasound was for increased breast density or another mammographic finding is unknown. Survey responses were self-reported and not validated by medical records. Another limitation is that the NHIS public-use data withholds state geographic identifiers needed to analyze associations with state laws on dense breast notification.3

Looking towards the future, primary care providers are likely to receive mammogram reports with information about increased breast density.5 Implications for clinicians, patient education, and research include how to best communicate information about dense breast tissue to women, and what are the appropriate additional tests.5 In 2016, the US Preventive Services Task Force concluded that scientific evidence was insufficient to assess the balance of benefits and harms of adjunctive screening in women with dense breast tissue on an otherwise negative screening mammogram.2 Examples of research topics that might be beneficial to clinical practice include the use of breast cancer risk calculators1 as part of discussions about increased breast density, and studies to identify effective adjunctive screening tests.6