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Risk of Malignancy Index (RMI-1) for Adnexal Mass

RMI-1 = U × M × CA-125, where U is 0 (no ultrasound features), 1 (one feature) or 3 (2–5 features) and M is 1 (premenopausal) or 3 (postmenopausal). An RMI ≥200 indicates high risk of ovarian malignancy (sensitivity 85%, specificity 97% in the derivation study) and supports referral to gynaecologic oncology.

  • Multilocular cyst (yes/no, +1)
  • Solid areas (yes/no, +1)
  • Evidence of metastases (yes/no, +1)
  • Ascites (yes/no, +1)
  • Bilateral lesions (yes/no, +1)
  • Menopausal status: Premenopausal; Postmenopausal (>1 year amenorrhoea, or >50 years after hysterectomy)
  • Serum CA-125 (U/mL)
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Interpretation

ResultMeaning
< 200Lower risk; manage per clinical context
≥ 200High risk of malignancy; gynaecologic oncology referral

Formula

RMI-1 = U × M × CA-125 (U/mL). U: 0 features = 0, 1 feature = 1, 2–5 features = 3 (multilocular cyst, solid areas, metastases, ascites, bilateral lesions). M: premenopausal = 1, postmenopausal = 3.

Clinical pearls

  • Later variants (RMI-2, Tingulstad 1996, using U and M of 1 or 4; RMI-3, Tingulstad 1999) give different values; this is the original Jacobs RMI-1 used in the RCOG Green-top guideline.
  • CA-125 is raised by endometriosis, fibroids, pregnancy, menstruation, PID and any cause of peritoneal irritation, which inflates RMI in premenopausal women.
  • If no ultrasound feature is present, U = 0 and RMI is 0 regardless of CA-125. IOTA Simple Rules or ADNEX may perform better in expert hands.

Examples

rmi postmenopausal multilocular cyst with solid areas, ca125 85risk of malignancy index premenopausal, bilateral, ca-125 150RMI for a 62 year old postmenopausal woman, ascites and solid mass, CA125 300

FAQ

What RMI score needs referral?

An RMI-1 of 200 or more is the usual threshold for referral to a gynaecologic oncology team.

What ultrasound features are used in the RMI?

Multilocular cyst, solid areas, metastases, ascites and bilateral lesions. None scores U = 0, one scores U = 1 and two or more score U = 3.

Evidence

  1. Jacobs I et al. A risk of malignancy index incorporating CA 125, ultrasound and menopausal status for the accurate preoperative diagnosis of ovarian cancer. Br J Obstet Gynaecol 1990;97:922–9.

Hematology & Oncology · Reviewed 2026-10-14 · Methodology