Is the Risk of Malignancy Index cutoff of 180–200 still used to assess ovarian cancer risk?

Is the RMI Cutoff of 180-200 Still Used?

The Risk of Malignancy Index (RMI) with a cutoff of 200 remains a valid and widely used tool for triaging ovarian masses, but it has been largely superseded by more accurate ultrasound-based systems like O-RADS and IOTA Simple Rules in contemporary practice, particularly in specialized centers.

Current Guideline Recommendations

The most recent ACR guidelines (2024) 1 and the O-RADS consensus (2020) 2 have shifted away from RMI as the primary risk stratification tool. Instead, these guidelines emphasize:

• O-RADS US classification system as the preferred standardized approach for adnexal mass characterization
• IOTA Simple Rules as an alternative validated system
• Transvaginal ultrasound with standardized descriptors rather than combined clinical-biochemical indices

The O-RADS system stratifies masses into categories 0-5 with specific risk percentages (O-RADS 3: 1-10%, O-RADS 4: 10-50%, O-RADS 5: ≥50% malignancy risk) and provides clear management pathways without requiring CA-125 levels 2. Notably, the O-RADS committee deliberately chose not to mandate routine tumor marker use, stating that "tumor marker evaluation should be individualized" and that CA-125 can be misleading in premenopausal women with endometriosis 2.

RMI Performance in Recent Studies

Despite guideline evolution, RMI at cutoff 200 continues to demonstrate reasonable diagnostic accuracy:

Sensitivity and Specificity

• Most recent validation (2026): 86.4% sensitivity, 78% specificity, 81.7% accuracy 3
• 2023 menopausal cohort: 75.8% sensitivity, 91.8% specificity 4
• 2012 tertiary center: 92% sensitivity, 82% specificity 5

Key Findings

The 2023 study 4 found that RMI cutoff of 241.5 performed better than 200 (96% sensitivity, 94.7% specificity), and a 2020 study 6 suggested that cutoffs of 250-300 may be more efficient with >90% accuracy.

Comparative Performance

IOTA Simple Rules outperform RMI in head-to-head comparisons:

• 2025 study 7: IOTA SR showed 94.4% sensitivity vs RMI-IV 88% sensitivity
• 2024 study 8: IOTA SR demonstrated 88.9% sensitivity and 94.1% specificity vs RMI-1 (45.5% sensitivity, 93.2% specificity)
• O-RADS showed 96.8% sensitivity vs IOTA 92.1% 2

Clinical Context for RMI Use

RMI remains appropriate in settings where:

• Specialized ultrasound expertise is unavailable 9
• Resource-limited environments require simple triage tools
• Initial referral decisions to gynecologic oncology centers are needed 5, 10

The 2006-2016 studies 9, 10 demonstrated RMI's effectiveness for referral triage to tertiary centers, with 87-88% sensitivity for identifying cases requiring specialist care.

Critical Caveats

• RMI has lower sensitivity in borderline tumors and early-stage cancers 9
• CA-125 alone is unreliable in premenopausal women (can be elevated in endometriosis, fibroids) 2
• Menopausal status, CA-125 ≤35, and absence of solid components significantly affect RMI accuracy 3
• The cutoff of 200 may be too low; consider 250-300 for better specificity 6

Practical Algorithm

1. First-line: Perform transvaginal ultrasound with O-RADS or IOTA classification 1, 2
2. If specialized ultrasound unavailable: Calculate RMI using cutoff 200-250
3. RMI ≥200: Refer to gynecologic oncology for evaluation 5, 10
4. RMI <200 with suspicious features: Consider MRI or specialist ultrasound review 2
5. Do not rely on CA-125 alone for decision-making in premenopausal women 2

Bottom line: While RMI cutoff 180-200 is still used and validated, modern practice favors ultrasound-based classification systems (O-RADS, IOTA) that demonstrate superior diagnostic performance and don't require biochemical markers 2, 7, 8.