Enter the CA-125 and select menopausal status to calculate the RMI.
Risk of Malignancy Index (RMI I)
0
- Ultrasound score (U)
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- Menopausal score (M)
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- CA-125
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- Features ticked
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RMI I is a triage tool for adnexal masses, not a diagnosis. Interpret it alongside imaging, clinical assessment and the multidisciplinary team’s judgement.
RMI Calculator (Risk of Malignancy Index I)
The Risk of Malignancy Index (RMI) is a scoring system used to assess how likely it is that an ovarian or pelvic (adnexal) mass is malignant, before surgery. It combines three things: the ultrasound appearance, whether the woman is pre- or post-menopausal, and the level of the blood marker CA-125. This calculator uses RMI I, the version recommended by NICE in England and Wales and the most widely used.
How RMI I is calculated
RMI I = U × M × CA-125
| Component | How it is scored |
|---|---|
| Ultrasound score (U) | One point for each of: multilocular cyst, solid areas, bilateral lesions, ascites, intra-abdominal metastases. U = 0 for 0 points, U = 1 for 1 point, U = 3 for 2–5 points. |
| Menopausal status (M) | M = 1 if pre-menopausal, M = 3 if post-menopausal. |
| CA-125 | Serum level in U/mL (IU/mL). |
“Post-menopausal” means a woman who has had no period for more than a year, or a woman over 50 who has had a hysterectomy.
Interpreting the result
- RMI I of 250 or more: NICE recommends referring the woman to a specialist gynaecological cancer multidisciplinary team.
- The original cut-off of 200: when the index was first described (Jacobs et al., 1990), a threshold of 200 gave 85% sensitivity and 97% specificity. Some units still use 200, so this calculator flags results between 200 and 249 so you can follow your local protocol.
- Below the threshold does not exclude cancer. The RMI is a triage tool that helps decide where a woman should be managed, not a diagnosis.
Limitations
- CA-125 can be raised by benign conditions including endometriosis, fibroids, pelvic inflammatory disease, menstruation, pregnancy, liver disease and heart failure, and it may be normal in some early or mucinous cancers.
- The RMI is less specific in pre-menopausal women.
- The ultrasound features depend on the operator’s experience and the quality of the report, which needs to describe each feature.
- Other versions (RMI II, III and IV) exist, but they haven’t shown a clear clinical advantage over RMI I.
- It is not a screening test for women without a known pelvic mass.
Frequently asked questions
What is a high RMI?
NICE uses an RMI I of 250 or more as the threshold for referral to a specialist gynaecological cancer team. The original 1990 study used 200.
Why is the RMI 0 when no ultrasound features are ticked?
The ultrasound score U is a multiplier. With no features present U is 0, so the product is 0 whatever the CA-125 is. A raised CA-125 with a normal scan still needs clinical assessment.
Can the RMI diagnose ovarian cancer?
No. It estimates the risk that a mass is malignant so that women can be triaged to the right service. Diagnosis depends on further imaging, surgery and histology.
Is the RMI valid in pre-menopausal women?
It can be used, but it’s less specific because benign conditions often raise CA-125 in younger women. Interpret it with extra caution.
What units is CA-125 measured in?
U/mL and IU/mL are the same, and either can be entered here.
Medical disclaimer
This calculator is an aid for healthcare professionals. It does not diagnose ovarian cancer and must not be used to make treatment decisions on its own. Decisions about investigation and referral rest with the responsible clinician and the multidisciplinary team, following local and national guidelines.
Sources & references
- NICE. Ovarian cancer: recognition and initial management (CG122) — Appendix: Risk of malignancy index (RMI I). nice.org.uk
- NICE. Ovarian cancer quality standard (QS18) — Statement 4: Malignancy indices. nice.org.uk/guidance/QS18
- Jacobs I, et al. “A risk of malignancy index incorporating CA 125, ultrasound and menopausal status for the accurate preoperative diagnosis of ovarian cancer.” British Journal of Obstetrics and Gynaecology, 1990. research.manchester.ac.uk