The diagnostic tool had become unreliable the moment patients chose alternatives to tampons.
For decades, medicine has measured the invisible through the mundane — how often a woman changes a tampon — trusting that this small act could reveal something serious about her health. But as menstruating people quietly shifted toward cups, discs, and period underwear, the diagnostic language stayed behind. A study from Oregon Health & Science University now makes plain what was hiding in that gap: a product holding 80 times more blood than another renders the old questions meaningless, and with them, the diagnoses that depend on honest answers.
- One in three menstruating people experience heavy bleeding, a condition linked to iron deficiency and serious underlying disease — yet the tool used to catch it was built for a world of tampons and pads alone.
- Researchers tested 21 products with real human blood and found a staggering range: a menstrual disc holds up to 80mL while period underwear holds just 1mL, meaning two patients describing identical habits could have blood loss differing by a factor of eighty.
- Manufacturers test their products with saline, not blood — so advertised capacities bear little resemblance to real-world performance, compounding the confusion clinicians already face.
- A patient choosing a menstrual cup for environmental reasons may describe her cycle in terms that sound normal to her doctor, while a serious condition quietly goes undiagnosed and untreated.
- The fix is disarmingly simple — ask patients which products they use before assessing blood loss — but it requires medicine to acknowledge that its diagnostic framework has silently become obsolete.
A team at Oregon Health & Science University set out to answer a deceptively simple question: how much blood can a menstrual cup actually hold? The answer, published in BMJ Sexual & Reproductive Health, exposed a diagnostic crisis hiding in plain sight.
For years, clinicians have assessed heavy menstrual bleeding by asking how often a patient needs to change a tampon or pad — a metric built for traditional products and never updated. Roughly one in three menstruating people experience heavy bleeding, a condition that can cause iron deficiency, fatigue, and sometimes signal serious disease. Catching it early matters. But the standard diagnostic tool, the Pictorial Blood Loss Assessment Chart, was designed around tampons, the only products subject to standardized absorption testing.
The researchers tested 21 menstrual products using expired human blood cells from a pathology lab. The results were striking: a Chinese menstrual disc held 80 milliliters — a volume that alone would indicate abnormal bleeding — while period underwear held just 1 milliliter. Cups fell somewhere between. The old clinical shorthand, "change your product every one to two hours," could now describe wildly different realities depending on what a patient was using.
The problem runs deeper than arithmetic. Menstrual blood is thicker and more complex than the saline manufacturers use in lab testing, meaning advertised capacities often bear little resemblance to real-world performance. A patient with genuine heavy bleeding might be using a menstrual cup out of environmental conviction, describe her cycle in familiar terms, and leave her doctor's office with no diagnosis — and no treatment for whatever is causing her condition.
The researchers' conclusion was simple but consequential: clinicians must ask patients which products they use before interpreting any description of blood loss. It sounds obvious in retrospect. But it marks a necessary reckoning — a diagnostic framework built for one generation of products had quietly become unreliable, and restoring it requires nothing more than asking a question that medicine had not thought to ask.
A team of researchers at Oregon Health & Science University set out to answer a deceptively simple question: how much blood can a menstrual cup actually hold? The answer, published in the BMJ Sexual & Reproductive Health, revealed a diagnostic crisis hiding in plain sight. When clinicians assess whether a patient has abnormally heavy menstrual bleeding, they rely on a decades-old metric: how often a woman needs to change a tampon or pad. But that metric was built for tampons and pads alone. It has not kept pace with the explosion of newer products—cups, discs, period underwear—that absorb vastly different amounts of blood.
The stakes are substantial. Roughly one in three menstruating people experience heavy menstrual bleeding, a condition that can trigger iron deficiency, fatigue, and sometimes signal serious underlying disease. Catching it early matters. But the diagnostic tool clinicians use, called the Pictorial Blood Loss Assessment Chart, was designed around traditional products. Only tampons undergo standardized industry testing for absorption. Manufacturers of cups, discs, and period underwear test their products with saline or other liquids—not actual blood. No one had bothered to measure what these newer products could actually hold when filled with real menstrual blood.
The researchers obtained expired human blood cells from the pathology lab and tested 21 different menstrual products. What they found was striking. A Chinese menstrual disc held 80 milliliters of blood—a volume that, on its own, would indicate heavy bleeding requiring medical attention. Period underwear held just 1 milliliter. A menstrual cup, depending on size and brand, fell somewhere in between. The gap between the smallest and largest products was enormous, and it meant that the old diagnostic language—"change your pad every one to two hours"—could mean something entirely different depending on which product a patient was using.
Consider the math. A woman using a menstrual disc would need to fill it completely three or four times across her entire cycle to reach the 80-milliliter threshold that signals abnormal bleeding. A woman using period underwear would need to use dozens of pairs. A clinician asking the standard questions would hear the same answer—"I go through products frequently"—but the actual blood loss could differ by a factor of eighty. The diagnostic tool, in other words, had become unreliable the moment patients started choosing alternatives to tampons and pads.
The problem runs deeper than simple math. Menstrual blood is thicker and more complex than the saline manufacturers use in their labs. It contains blood cells, vaginal secretions, endometrial tissue, and sometimes clots. Products that perform well in controlled testing might leak or overflow in real conditions. The manufacturers' advertised capacities, based on non-blood liquids, bore little resemblance to what the researchers actually measured. A product marketed as holding a certain amount might hold far less when faced with actual menstrual blood.
The implications are clinical and human. A patient with genuine heavy bleeding—the kind that causes iron deficiency and disrupts daily life—might be using a menstrual cup because it feels more sustainable or environmentally responsible. When she describes her bleeding to a doctor using the old metrics, the doctor might hear a normal pattern. The condition goes undiagnosed. The underlying cause, whether hormonal imbalance or something more serious, remains untreated. The patient continues to suffer.
The researchers' conclusion was straightforward but consequential: clinicians need to ask patients which menstrual products they use before assessing blood loss. It sounds obvious in retrospect. But it represents a shift in how medicine approaches a condition that affects millions of people. The diagnostic framework, built for one generation of products, had silently become obsolete. Fixing it requires nothing more than asking a question—but that question has to be asked, and the answer has to change how doctors interpret what they hear.
Citações Notáveis
Clinicians have not yet modified metrics for diagnosing heavy menstrual bleeding despite the wide availability and use of new commercially available menstrual products, such as menstrual cups and discs.— Study findings
A Conversa do Hearth Outra perspectiva sobre a história
Why does it matter what product someone uses? Isn't heavy bleeding heavy bleeding?
Not in the way doctors measure it. They ask how often you change your tampon. But if you're using a disc that holds eighty times more blood than period underwear, that question means nothing.
So a doctor could miss heavy bleeding entirely.
Exactly. A patient with real, dangerous bleeding might describe a pattern that sounds normal through the old lens. The condition stays invisible.
How many people are we talking about?
About one in three menstruating people experience heavy bleeding. If they're using newer products, the diagnostic tool breaks down for all of them.
What happens if it goes undiagnosed?
Iron deficiency, exhaustion, sometimes serious underlying conditions that need treatment. The bleeding itself can signal something that needs medical attention.
So the fix is just asking what product they use?
It's a start. But it means doctors have to know that the old metrics don't work anymore, and they have to ask the question in the first place.