The CA-125 blood test measures the concentration of Cancer Antigen 125, a protein classified as a tumor biomarker, in the bloodstream. This substance may be produced by cancer cells or by healthy cells in response to cancer or other non-cancerous conditions. While low levels of CA-125 are normally found in the body, elevated amounts are often associated with specific health concerns. The test is primarily employed in the management of certain cancers, providing a quantitative value to help guide medical decisions and monitor patient health.
Purpose of the CA-125 Test
A healthcare provider requests a CA-125 test for specific medical indications, most commonly after a cancer diagnosis is established. The primary application is monitoring treatment effectiveness for cancers, particularly ovarian, fallopian tube, and primary peritoneal cancers. A consistent decline in CA-125 levels suggests the patient is responding favorably to therapy.
The test is also used as a surveillance tool for individuals who have completed cancer treatment to check for potential disease recurrence. A rising trend in the CA-125 value can signal that the cancer may have returned or is progressing, prompting further evaluation. Physicians may also order the test when evaluating a pelvic mass detected during a physical exam or on imaging.
The CA-125 result is considered alongside imaging and physical findings to help determine the likelihood that the mass is malignant. For a small subset of the population at very high risk for ovarian cancer (due to strong family history or genetic mutations like BRCA1 or BRCA2), the test may be used for screening. However, even in high-risk cases, it is often performed with transvaginal ultrasound, as neither test is accurate enough on its own.
Steps to Obtaining the Test
Obtaining a CA-125 blood test requires a physician’s order or prescription; it cannot be ordered over-the-counter without a clinical reason. Your ordering physician (gynecologist, oncologist, or primary care provider) will send the request to a laboratory facility. The blood draw is a routine venipuncture procedure performed by a phlebotomist.
You can have your blood drawn at various locations, including hospital-affiliated laboratories, specialized clinics, or independent commercial lab centers like Quest Diagnostics or Labcorp. Scheduling is straightforward, as the test generally does not require special preparation, such as fasting. Inform the lab staff if you are taking biotin supplements, as high doses can interfere with results.
Turnaround time for results varies but is typically one to five business days, reported directly to your ordering physician. The cost depends on your health insurance plan, deductible, and the facility performing the analysis. When ordered for a covered medical indication, the test is often covered by insurance, though co-pays or co-insurance may apply.
Cost and Coverage
For those paying out-of-pocket, the cost can range widely. It is advisable to check with both the lab and your insurance provider beforehand, using the billing code provided by your doctor.
Understanding the Test Results
The results are reported in units per milliliter (U/mL), with the accepted upper limit for the normal range generally considered 35 U/mL. This threshold can vary slightly between laboratories. While readings below 35 U/mL are expected, some healthy individuals may naturally have values slightly above this level.
A significant limitation of the CA-125 test is its lack of specificity; an elevated result does not definitively diagnose cancer. Numerous non-cancerous conditions can cause the CA-125 level to rise above the normal range, including:
- Endometriosis
- Uterine fibroids
- Pelvic inflammatory disease
- Liver disease
- Menstruation or early pregnancy
Due to the high rate of false-positive results, the CA-125 test is not recommended for routine screening of the general population. If your result is elevated, your physician will recommend additional diagnostic procedures, such as advanced imaging or a biopsy. When monitoring for cancer, the trend of the number over time is the most meaningful indicator of disease status, not a single value.
If an elevated result is received, consult with a specialist, such as a gynecologic oncologist, experienced in interpreting these biomarkers. They synthesize the CA-125 data with other clinical information to determine the appropriate next steps. Even with cancer present, the CA-125 level may not be elevated (a false negative), emphasizing the need for comprehensive medical evaluation.