BI-RADS Classification Calculator — Breast Imaging Reporting & Data System
The Breast Imaging Reporting and Data System (BI-RADS) is a standardized classification system developed by the American College of Radiology (ACR) for reporting mammography, ultrasound, and MRI findings of the breast. It provides clear assessment categories, malignancy risk ranges, and management recommendations to ensure consistent interpretation and communication of breast imaging results.
About
BI-RADS was first introduced in 1993 by the American College of Radiology to standardize mammography reporting terminology. It has since been expanded to include ultrasound and MRI, with the 5th edition published in 2013. The system uses a final assessment category from 0 to 6, with Category 4 subdivided into 4A (low suspicion, 2-10% malignancy), 4B (moderate suspicion, 10-50%), and 4C (high suspicion, 50-95%). The assigned category determines the malignancy risk estimate and guides subsequent management, ranging from routine screening to biopsy to definitive treatment. BI-RADS also standardizes breast density reporting (A-D categories) and includes a structured reporting lexicon for lesion descriptors. The system has been widely adopted internationally and is required by the Mammography Quality Standards Act (MQSA) in the United States.
Formula
BI-RADS Category = 0 (Incomplete) / 1 (Negative) / 2 (Benign) / 3 (Probably Benign) / 4A-C (Suspicious) / 5 (Highly Suggestive) / 6 (Known Malignancy)
BI-RADS assessment categories are assigned by the interpreting radiologist based on characteristic imaging findings. Category 0: Incomplete — needs additional imaging evaluation before final assessment. Category 1: Negative — no findings to report, routine screening. Category 2: Benign — benign findings (e.g., calcified fibroadenoma, fat-containing lesions, simple cysts), return to routine screening. Category 3: Probably Benign — <2% malignancy risk, short-interval follow-up recommended (typically 6 months). Category 4: Suspicious — biopsy should be considered, further subdivided: 4A (low suspicion, 2-10%), 4B (moderate suspicion, 10-50%), 4C (high suspicion, 50-95%). Category 5: Highly Suggestive of Malignancy — ≥95% malignancy risk, requires biopsy and definitive management. Category 6: Known Biopsy-Proven Malignancy — used for pre-treatment staging, neoadjuvant therapy monitoring, and surgical planning.
Score Interpretation
BI-RADS is the standard classification system for breast imaging worldwide, mandated by the Mammography Quality Standards Act (MQSA) in the United States and adopted by radiology societies globally. The standardized lexicon eliminates variability in mammography reporting terminology, ensuring that referring physicians receive clear assessment categories with defined malignancy risk ranges. This enables consistent management decisions, from routine screening to biopsy referral. The subdivision of Category 4 into 4A, 4B, and 4C reflects the heterogeneous malignancy risk within the suspicious category and allows more nuanced clinical decision-making. BI-RADS also standardizes breast density reporting (categories A-D), which is important because dense breast tissue is an independent risk factor for breast cancer and can mask lesions on mammography. The system is periodically updated by the ACR based on new evidence and imaging technologies.
Category 0 — Incomplete — 0–0
Need additional imaging evaluation. No malignancy risk assigned.
Management: Obtain additional mammographic views, ultrasound, or MRI as appropriate.
Category 1 — Negative — 1–1
0% malignancy risk. Routine screening.
Management: Continue routine age-appropriate screening mammography.
Category 2 — Benign — 2–2
0% malignancy risk. Benign findings.
Management: Return to routine screening. No additional imaging needed.
Category 3 — Probably Benign — 3–3
<2% malignancy risk. Short-interval follow-up.
Management: Short-interval follow-up (6 months). If stable at 6 and 12 months, return to routine screening.
Category 4 — Suspicious — 4–4
2-95% malignancy risk depending on subcategory. Biopsy recommended.
Management: Recommend biopsy. Risk varies: 4A (2-10%), 4B (10-50%), 4C (50-95%).
Category 5 — Highly Suggestive of Malignancy — 5–5
≥95% malignancy risk. Biopsy and definitive management.
Management: Biopsy and definitive management. Surgical oncology consultation recommended.
Category 6 — Known Biopsy-Proven Malignancy — 6–6
Known malignancy. Imaging for staging and treatment planning.
Management: Proceed with definitive treatment plan. Use for staging, treatment planning, and response monitoring.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Women undergoing breast imaging | Categories 0-6 with defined malignancy risk ranges | BI-RADS 1-2 return to routine screening; BI-RADS 3 short follow-up; BI-RADS 4-6 biopsy and management. |
Dr. Mahmoud El-Sayed
Dr. Mahmoud is an endocrinology consultant with expertise in oncological assessment and imaging classification systems.
View medical review board & editorial policy →Example Calculation
A 52-year-old woman undergoes screening mammography. The study reveals a new, irregular, spiculated mass in the right upper outer quadrant measuring 1.8 cm with associated pleomorphic microcalcifications. There is no prior comparison study available. The radiologist assigns BI-RADS Category 4C (high suspicion of malignancy, 50-95% risk). An ultrasound-guided core needle biopsy is performed, revealing invasive ductal carcinoma (IDC), grade 2, estrogen receptor positive, HER2 negative. The patient is referred for surgical oncology consultation and definitive management.
Related Conditions
Related Medications
Common Mistakes
Using BI-RADS 3 as a "suspicious" category
BI-RADS 3 is "probably benign" with <2% malignancy risk and warrants short-interval follow-up, NOT biopsy. Category 4 is the suspicious category requiring biopsy consideration.
Not subcategorizing Category 4
Category 4 should always be subdivided into 4A, 4B, or 4C to convey the degree of suspicion and guide appropriate management and patient counseling.
Assigning BI-RADS 0 for incomplete workup without recommending specific additional views
When using Category 0, specify which additional imaging modalities are needed (e.g., spot compression, ultrasound, MRI) to guide the referring physician.
Frequently Asked Questions
What is the difference between BI-RADS 3 and BI-RADS 4?
Can BI-RADS 3 be used for MRI?
How are breast density categories reported in BI-RADS?
References
- D'Orsi CJ, Sickles EA, Mendelson EB, et al. ACR BI-RADS Atlas, Breast Imaging Reporting and Data System. 5th ed. Reston, VA: American College of Radiology; 2013.
- Sickles EA, D'Orsi CJ, Bassett LW, et al. ACR BI-RADS Mammography. In: ACR BI-RADS Atlas, Breast Imaging Reporting and Data System. 5th ed. Reston, VA: American College of Radiology; 2013.
- Mendelson EB, Böhm-Vélez M, Berg WA, et al. ACR BI-RADS Ultrasound. In: ACR BI-RADS Atlas, Breast Imaging Reporting and Data System. 5th ed. Reston, VA: American College of Radiology; 2013.
- Morris EA, Comstock CE, Lee CH, et al. ACR BI-RADS Magnetic Resonance Imaging. In: ACR BI-RADS Atlas, Breast Imaging Reporting and Data System. 5th ed. Reston, VA: American College of Radiology; 2013.