Could the secret to diagnosing endometriosis be hiding in plain sight?
Although menstrual blood is typically discarded, researchers are beginning to use it to reveal new clues about women’s health.
For those who experience menstruation, period blood is something that’s often discarded without a second thought. But what if it held just as much value as urine, cervical, and other blood samples that are used to examine uterine health?
“The uterus is kind of like one of the last frontiers to be investigated on a really thorough level,” says Christine Metz, professor of obstetrics and gynecology, as well as molecular medicine, at the Feinstein Institutes for Medical Research at Northwell Health in New York state.
Metz and other researchers are currently exploring the potentials of period blood. This substance—medically referred to as “effluent” and consisting of a combination of some blood, but also uterine tissue, immune cells, mucus, proteins, and signaling molecules—reflects what is happening inside the uterus during the menstrual cycle and carries a rich set of biological information, says Dipanjan Pan, professor in nanomedicine at The Pennsylvania State University.
Research in this space has picked up over the last decade or so, with a 2024 study in The Annals of Medicine & Surgery suggesting the blood can be a valuable source of health information—and has the potential to "revolutionize healthcare” for those who menstruate. Although there is potential for period blood to help with monitoring mechanisms like blood sugar and vitamin deficiencies as well as tracking immune and inflammatory health and screening for other gynecological diseases and sexually transmitted infections such as HPV, the most promising work may be for diagnosing endometriosis.
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How period blood could help diagnose endometriosis
Metz has been working with period blood through the Research OutSmarts Endometriosis (ROSE) study she co-launched in 2013 to better understand endometriosis and work toward developing a non-invasive diagnostic tool. Endometriosis—which affects an estimated 10 percent, or 190 million, of reproductive-age women worldwide—is typically diagnosed with an endometrial biopsy via surgery under general anesthesia, which is about 70 percent accurate and sometimes requires two or three surgeries before a diagnosis can be made. But period blood, Metz says, has the potential to act as a “natural biopsy”—once more research has been conducted, of course.
Research by Metz and her team, published in BMC Medicine in 2022, demonstrates clear differences in the menstrual blood of people with endometriosis versus those without by using single cell RNA sequencing analysis of the endometrial tissue. “If you combine that with clinical information about the patient's symptoms, we think we have a very good handle on diagnosing endometriosis,” she says.
It’s also easier to obtain a control sample from a healthy individual via period blood as opposed to a surgery. This way, “you can really do population-based research because people can collect [the sample] at home,” she says.
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What’s more, it can take between four and 12 years to receive an endo diagnosis, according to the World Health Organization. This is because there is no standard protocol for diagnostic surgery for endometriosis. Surgeons “don't have to take images to prove that there wasn't anything there and they looked in every single spot,” Metz says, so they can often miss microscopic lesions.
Other reasons for the lag in diagnosis can be because the lesions in teens and young adults are too early to spot and diagnose with this method, that people want to avoid invasive surgery for a definitive diagnosis, and that women’s pain is often dismissed.
But people in the ROSE study may get diagnosed in the same year their symptoms start, Metz says.
She imagines a future in which patients would get a kit in the mail to send in samples that they collect at home. From there, the team could begin studying better treatment options. “We've never had a clinical trial in women to find out whether hormone treatments do indeed stop progression of [endometriosis] because we've never had a platform for early diagnosis,” she says.
How period blood can help diagnose other conditions
It’s possible that menstrual blood could also be used to diagnose other conditions, such as adenomyosis, the equivalent of endometriosis of the uterus itself; chronic endometritis, or inflammation of the endometrial lining; uterine fibroids, and other forms of infertility, Metz says.
In the cases of adenomyosis and endometritis, period blood could contain cells from the uterine lining that are pathologically different than blood from our veins and could be identified using single cell RNA sequencing or other approaches.
The current diagnostic methods, primarily biopsy, for endometritis are “fraught with diagnostic issues,” Metz says, including that the small part of the uterus that is typically biopsied may not be infected. “We currently have preliminary data in patients with chronic endometritis supporting the fact that we could identify some of these unique markers in the tissues that we obtain [in period blood].”
Additionally, period blood could help with monitoring immune and inflammatory health. “Unlike circulating blood, menstrual effluent contains not just blood, but also endometrial tissue, immune cells, and local inflammatory mediators,” says Pan. “In many ways, menstrual effluent provides a localized, high-resolution snapshot of immune and inflammatory activity, something peripheral blood often dilutes or misses.”
The opportunity, he says, is to use this as a non-invasive window into reproductive and even systemic immune health. Although more research is needed, one day women might be able to see if their immune defenses are down and are perhaps more susceptible to—or already have—an illness or infection, he says.
This may also explain why period blood could help diagnose STIs such as HPV, which could ultimately lead to pre-cancerous lesions and cervical cancer, per a 2024 study in Diagnostics. A more recent 2026 study in the BMJ found that mini pad collection of period blood is a comparable diagnostic to clinician collected cervical samples for HPV testing.
There’s also the potential to leverage the fluid to understand a patient’s environmental exposures, such as to microplastics, air pollution, and forever chemicals. In one study published in 2022 in Science of the Total Environment, Metz and co-authors found that chemical exposures linked to reproductive toxicity and endocrine disruption were present in menstrual blood. Since the substance is flushed out each month, it provided researchers a unique way to study these exposures.
The unique challenges researchers face
Though the new research and products are promising, it doesn’t come without challenges. For one, Bethany Samuelson Bannow, director of classical hematology at the Cleveland Clinic Foundation, says that it’s hard to study certain aspects of period blood if it’s been sitting in a menstrual cup and therefore not “fresh.” Many are also not comfortable using an insertion product like a menstrual cup.
Another hurdle is that menstrual fluid varies significantly from person to person and even from cycle to cycle, Pan says. “Hormones, age, medications, and underlying health conditions can all influence the composition of the sample, making it harder to identify consistent biomarkers.”
Innovations like “smart” pads that collect the samples and analyze them in real time may help solve some of these problems. Additionally, when the sample sits in a menstrual cup for hours, Samuelson Bannow says, the process of clotting and clot breakdown can continue, leading to an increase in its breakdown. This leaves the substance unusable for research purposes.
Pan believes that in the next five to 10 years, there may be readily available at-home or point-of-care tests leveraging period blood for endometriosis as well as for STIs like HPV. “I anticipate that many direct-to-consumer technologies will emerge, giving women the opportunity to test earlier, gain insights sooner, and ultimately make more informed decisions about their health,” he says.
As for Metz, she says that even though some of the innovations being tested aren’t ready for prime time, there are “great strides” being made—including awareness around the fact that period blood isn’t just a waste product. “When I talk to people, they're so excited that it could be useful,” Metz says. “Menstrual blood is just really a treasure trove of information.”
