Definitional Guide

What Is BI-RADS®?

The ACR Breast Imaging Reporting and Data System: assessment categories 0-6 explained for the breast imaging professionals who use them every day.

Last Reviewed: August 25, 2026

ACR Standard7 Assessment CategoriesScreening & Diagnostic5th Edition (2013)

BI-RADS® in Plain Language

BI-RADS® stands for the Breast Imaging Reporting and Data System, a standardized framework created by the American College of Radiology (ACR) that gives every radiologist in the country a common language for describing mammography findings and a consistent set of categories for communicating what should happen next.

Note on FDA Regulatory Terminology

The FDA’s regulations (21 CFR Part 900) refer to these as “imaging assessment categories,” not BI-RADS® categories. In clinical practice, the two systems align closely, but FDA inspectors and MQSA audit requirements use imaging assessment terminology. See the FDA taxonomy section below for the complete list of regulatory categories.

Before BI-RADS®, radiology reports varied enormously from facility to facility. One radiologist might call a finding “suspicious” while another described the exact same finding as “indeterminate.” Referring physicians had no reliable way to know whether a report meant “get a biopsy today” or “come back in six months.” BI-RADS® solved this by creating seven defined assessment categories, 0 through 6, each with a specific clinical meaning and a specific management recommendation.

BI-RADS® is also the foundation of the MQSA medical outcome audit. The audit tracks positive mammographic findings, defined by their BI-RADS® assessment category, and correlates them with biopsy results and pathology outcomes. Without consistent BI-RADS® categorization, the audit’s core performance metrics cannot be reliably calculated.

1992

First Edition Published

2013

Current (5th) Edition

7

Assessment Categories

ACR

Governing Body

The BI-RADS® Assessment Categories

Each category carries a specific clinical meaning and a defined management recommendation.

0

BI-RADS® 0: Incomplete

Additional imaging needed before a final assessment can be made. Primary driver of recall rate in screening mammography.

Management: Additional evaluation

1

BI-RADS® 1: Negative

No abnormality identified. Breasts are symmetrical with no masses, distortion, or calcifications.

Management: Routine annual screening

2

BI-RADS® 2: Benign

A finding is present but is definitively benign, no malignant potential. Examples include calcified fibroadenomas and fat-containing lesions.

Management: Routine annual screening

3

BI-RADS® 3: Probably Benign

Finding with less than 2% likelihood of malignancy. Short-interval surveillance recommended. Requires follow-up tracking.

Management: 6-month short-interval follow-up

4

BI-RADS® 4: Suspicious

Finding with intermediate likelihood of malignancy. Subdivided: 4A (>2-10%), 4B (>10-50%), 4C (>50-<95%). Biopsy is recommended.

Management: Tissue sampling (biopsy)

5

BI-RADS® 5: Highly Suggestive of Malignancy

Greater than 95% likelihood of malignancy. The appearance is virtually diagnostic of breast cancer. Biopsy is required.

Management: Biopsy required

6

BI-RADS® 6: Known Malignancy

Used only for imaging performed on a lesion already confirmed malignant by prior biopsy. Used in staging and surgical planning context.

Management: Surgical/treatment planning

FDA Imaging Assessment Categories (21 CFR Part 900)

The FDA’s regulations at 21 CFR 900.12(c)(1) define “imaging assessment categories”, the regulatory term used in MQSA inspections and audits. The FDA taxonomy includes more categories than the BI-RADS® 0-6 numbering system alone. Facilities and inspectors use this language; BI-RADS® categories align closely but do not map one-to-one in all cases.

(A)

Negative

BI-RADS® 1

No significant abnormality to report. Routine annual screening recommended.

(B)

Benign

BI-RADS® 2

A finding is present but is definitively benign, no malignant potential. Routine annual screening recommended.

(C)

Probably Benign

BI-RADS® 3

Finding with a very low likelihood of malignancy (less than 2%). Short-interval surveillance recommended.

(D)

Suspicious

BI-RADS® 4

Intermediate likelihood of malignancy. Biopsy recommended. Subdivided into 4A, 4B, 4C by degree of suspicion.

(E)

Highly Suggestive of Malignancy

BI-RADS® 5

Greater than 95% likelihood of malignancy. Biopsy required.

(F)

Known Biopsy-Proven Malignancy

BI-RADS® 6

Used only when imaging is performed on a lesion already confirmed malignant by prior biopsy. Surgical/treatment planning context.

(G)

Post-Procedure Mammogram for Marker Placement

FDA only, no BI-RADS® equivalent

Used after a biopsy or other procedure to confirm clip/marker placement. This FDA category has no direct BI-RADS® number equivalent.

0 (sub-type)

Incomplete: Need Additional Imaging Evaluation

BI-RADS® 0

Additional imaging views or other modalities (e.g., ultrasound) are needed before a final assessment can be assigned. Primary driver of recall rate in screening mammography.

0 (sub-type)

Incomplete: Need Prior Mammograms for Comparison

BI-RADS® 0

Prior mammograms are not available at the time of interpretation. The study cannot be fully assessed without comparison. This sub-type of BI-RADS® 0 is tracked separately in some audit systems.

The BI-RADS® Lexicon

Beyond Categories: Standardized Descriptive Vocabulary

BI-RADS® is more than a set of assessment numbers. The BI-RADS® Atlas also defines a precise vocabulary, called the lexicon, for describing the characteristics of every type of finding seen on mammography.

  • Masses: described by shape (round, oval, irregular), margin (circumscribed, obscured, microlobulated, indistinct, spiculated), and density (high, equal, low, fat-containing)
  • Calcifications: classified by morphology (amorphous, coarse heterogeneous, fine pleomorphic, fine linear/branching) and distribution (diffuse, regional, grouped, linear, segmental)
  • Architectural distortion: defined specifically as a distortion of normal breast architecture without a visible mass
  • Asymmetries: four types (asymmetry, global asymmetry, focal asymmetry, and developing asymmetry), each with distinct management implications
  • Associated features: skin thickening, skin retraction, nipple retraction, trabecular thickening, axillary adenopathy, and architectural distortion as a secondary finding

Consistent lexicon use directly affects audit data quality.

When radiologists apply BI-RADS® descriptors inconsistently, the resulting audit data is harder to interpret and harder to benchmark. Facilities with strong audit programs often use the lexicon to standardize report language across all interpreting physicians.

BI-RADS®: Frequently Asked Questions

Detailed answers to the questions breast imaging professionals ask most often about BI-RADS® categories, lexicon, and clinical application.

BI-RADS® stands for Breast Imaging Reporting and Data System. It is a standardized framework developed by the American College of Radiology (ACR) that provides a common language for describing mammography findings, a structured set of assessment categories for communicating recommendations, and guidance for managing patients based on those categories. BI-RADS® is also used in breast ultrasound and breast MRI, but it originated in and is most widely applied to mammography.

BI-RADS® was created by the American College of Radiology (ACR) to address a fundamental problem in breast imaging reporting: inconsistency. Before BI-RADS®, radiologists used highly varied terminology to describe the same findings, and recommendations for follow-up were often ambiguous. A referring physician receiving a report that said 'suspicious lesion, correlate clinically' had little actionable guidance. BI-RADS® standardized both the vocabulary used to describe findings (the lexicon) and the assessment categories used to communicate recommended next steps. The first edition was published in 1992; the current fifth edition was released in 2013.

There are seven BI-RADS® assessment categories for mammography: Category 0: Incomplete (additional imaging needed before a final assessment can be made); Category 1: Negative (no abnormality found; routine annual screening recommended); Category 2: Benign (a finding is present but is definitively benign; routine annual screening recommended); Category 3: Probably Benign (finding with less than 2% likelihood of malignancy; short-interval 6-month follow-up recommended); Category 4: Suspicious (biopsy recommended; subdivided into 4A, 4B, 4C by increasing suspicion); Category 5: Highly Suggestive of Malignancy (greater than 95% likelihood of malignancy; biopsy required); Category 6: Known Biopsy-Proven Malignancy (used when imaging is performed on a lesion already confirmed malignant).

A BI-RADS® 0 assessment means the mammogram is incomplete: additional imaging is needed before a final assessment can be made. BI-RADS® 0 is used primarily in screening mammography when a finding requires further evaluation with diagnostic views, additional imaging modalities (such as ultrasound), or comparison with prior mammograms not available at the time of interpretation. BI-RADS® 0 is the assessment category that drives the recall rate (Abnormal Interpretation Rate). In diagnostic mammography, BI-RADS® 0 should rarely if ever be used, because the diagnostic workup is designed to reach a definitive assessment during the same encounter.

A BI-RADS® 3 assessment, Probably Benign, is used when a finding has a very low but non-negligible likelihood of malignancy, generally defined as less than 2%. The standard management is short-interval follow-up imaging, typically at 6 months, rather than immediate biopsy. If the finding remains stable over a 2-year surveillance period, it may be reclassified as benign (BI-RADS® 2). BI-RADS® 3 should not be used as a default 'unsure' category, it has a specific definition tied to a specific management recommendation. BI-RADS® 3 assessments require careful tracking because the patient needs to return for follow-up imaging, and loss to follow-up in this category represents a real clinical risk.

A BI-RADS® 4 assessment, Suspicious, indicates a finding with an intermediate likelihood of malignancy for which biopsy is recommended. BI-RADS® 4 is subdivided into three sub-categories: 4A (low suspicion, greater than 2% but not more than 10% likelihood of malignancy); 4B (moderate suspicion, greater than 10% but not more than 50%); and 4C (high suspicion but not highly suggestive, greater than 50% but less than 95%). The subdivisions help guide clinical decision-making about the urgency and approach to tissue sampling and are important for PPV calculations in the medical outcome audit.

A BI-RADS® 5 assessment, Highly Suggestive of Malignancy, indicates a finding with greater than 95% likelihood of malignancy. Biopsy is required. BI-RADS® 5 findings have a characteristic appearance that virtually all radiologists would agree is malignant. In practice, the management goal for a BI-RADS® 5 finding is to proceed directly to the most definitive tissue sampling approach available, because a benign result on needle biopsy would be considered discordant and would typically lead to surgical excision regardless.

A BI-RADS® 6 assessment, Known Biopsy-Proven Malignancy, is used when imaging is performed on a lesion that has already been confirmed as malignant by prior tissue sampling. This category is not used for initial assessment; it is used in the staging and surgical planning context, when imaging is being performed to evaluate the known cancer's extent or monitor response to neoadjuvant therapy. BI-RADS® 6 findings are excluded from medical outcome audit recall rate calculations because they are not screening assessments.

MQSA does not specifically mandate the use of BI-RADS®, but the ACR BI-RADS® system has become the de facto standard for satisfying MQSA's requirement that mammography reports include a final assessment category that communicates whether additional imaging or biopsy is needed. MQSA requires standardized reporting that includes a clear recommendation for clinical management; BI-RADS® categories 0-6 provide the structured vocabulary for meeting that requirement. Additionally, MQSA's required medical outcome audit is built around BI-RADS® assessment categories, specifically all BI-RADS® 0, 4, and 5 assessments (and BI-RADS® 3 cases with biopsy recommendation) must be tracked and correlated with outcomes.

The BI-RADS® lexicon is a standardized vocabulary for describing the characteristics of breast imaging findings. In mammography, the lexicon includes precisely defined terms for masses (shape, margin, density), calcifications (morphology, distribution), architectural distortion, asymmetries, and associated features. Using the lexicon ensures that when one radiologist describes a finding as a 'round, circumscribed, equal-density mass,' another radiologist reading the report knows exactly what was seen. The lexicon reduces ambiguity in communication between radiologists, referring physicians, and follow-up providers, and supports more consistent and accurate audit tracking.

Yes, BI-RADS® assessment categories apply to both screening and diagnostic mammography, but they are used differently in each context. In screening mammography, the radiologist interprets the study without the patient present and issues a final assessment that is either negative/benign (BI-RADS® 1 or 2), probably benign (BI-RADS® 3, though uncommon in screening), or requires additional workup (BI-RADS® 0). In diagnostic mammography, the radiologist typically interprets with the patient present, can perform additional views during the encounter, and is expected to reach a definitive assessment (BI-RADS® 1-5) by the end of the visit. BI-RADS® 0 is rarely appropriate in diagnostic mammography because additional imaging can be performed immediately.

BI-RADS® assessment categories are the entry point for the medical outcome audit. The audit tracks every positive mammographic finding, defined as BI-RADS® 0, 4, 5, and BI-RADS® 3 with a biopsy recommendation, and correlates each with its clinical outcome. From this data, the audit calculates recall rate (percentage of BI-RADS® 0 assessments among all screening mammograms), cancer detection rate, and positive predictive values (PPV1, PPV2, PPV3). Accurate and consistent BI-RADS® categorization is therefore a prerequisite for meaningful audit data: an inconsistently applied BI-RADS® 0 category will directly distort the recall rate calculation on which MQSA compliance is evaluated.

How Mammologix Helps

BI-RADS®, Audits, and Compliance Support

Mammologix tracks mammographic assessments by BI-RADS® category, monitors follow-up completion for BI-RADS® 0 and 3 cases, and uses assessment data as the foundation for MQSA-compliant medical outcome audits. Our audit support includes pathology correlation, metric calculation, and physician-level reporting, built on the BI-RADS® categories your radiologists already use.

Medical Outcome AuditHow BI-RADS® assessments feed into the MQSA-required outcome audit: what the resulting metrics mean.Learn more →MammoTrackPatient tracking and follow-up workflows built around BI-RADS® assessment categories.Learn more →MammoComply: MQSA ComplianceMQSA inspection readiness, audit preparation, and ACR accreditation support.Learn more →AIR Score CalculatorCalculate your Abnormal Interpretation Rate (BI-RADS® 0 rate) vs. ACR benchmarks.Learn more →
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About the Author

RL
Richard D. Lippert, Jr.

Founder, President, and Chief Executive Auditor, Mammologix · Breast Imaging Operations since 1995

A registered radiologic technologist, Richard D. Lippert, Jr., Founder, President, and Chief Executive Auditor of Mammologix, has spent more than 30 years in breast imaging operations, from clinical practice and hospital radiology administration to building specialized service platforms for imaging centers nationwide. His work spans mammography tracking, lay communication, FDA/MQSA-related support, medical outcome audit, and the operational systems that help facilities stay compliant and keep patients from falling through the cracks.

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