A common condition that keeps slipping past a single blood test

Primary aldosteronism may affect as many as one in five people with high blood pressure, making it one of the more common identifiable causes of hypertension, yet it's also one of the most frequently missed. A study published in Science Translational Medicine, led by researchers at the University of Bristol and the University of Manchester alongside collaborators in Norway, Sweden, and Greece, helps explain why: the hormone surges driving the condition happen unpredictably throughout the day, and especially at night, precisely when routine blood tests are almost never performed.

Dr. Thomas Upton, a clinical research fellow at the University of Bristol and senior clinical fellow at Bristol Hospitals NHS Foundation Trust, framed the diagnostic stakes plainly, describing primary aldosteronism as an important and commonly missed cause of high blood pressure that current testing approaches struggle to catch reliably.

What actually goes wrong in this condition

Primary aldosteronism develops when the adrenal glands produce excess amounts of aldosterone, a hormone central to how the body regulates salt, water balance, and blood vessel tone. Too much aldosterone pushes blood pressure up directly, and the condition carries elevated risk for heart disease, stroke, diabetes, and other serious complications well beyond hypertension alone. What makes it a particularly frustrating diagnostic target is that standard clinical practice relies on a single blood sample, typically drawn during a routine daytime clinic visit, to check aldosterone levels against a diagnostic threshold. That approach assumes hormone levels stay roughly consistent enough that one snapshot in time reliably reflects the underlying condition.

This study demonstrates that assumption doesn't hold for a meaningful share of patients. Aldosterone levels, it turns out, fluctuate considerably more than clinical practice has generally accounted for.

How researchers actually caught the pattern

To capture what a single clinic visit couldn't, the research team used U-RHYTHM, a portable wearable device developed at the University of Bristol, roughly the size of a mobile phone and worn at the waist, that measures hormone levels every 20 minutes around the clock while patients go about their normal lives at home rather than staying confined to a hospital or research facility. That continuous, real-world monitoring approach is what let researchers see something a single blood draw structurally cannot: the actual shape of hormone production across a full 24-hour cycle, in a patient's own everyday environment rather than an artificial clinical setting.

Across 60 monitored patients, the team found that people with primary aldosteronism experience repeated bursts of hormone secretion during both waking hours and sleep, rather than either a flat, elevated baseline or a single predictable daily peak. Crucially, the daily hormonal rhythm itself remained intact; what changed was the appearance of extra, unpredictable surges layered on top of that normal rhythm, including a previously undocumented pattern of nighttime bursts.

Why the nighttime finding matters so much clinically

Dr. Eder Zavala, senior author on the study and a UKRI Future Leader Fellow at the University of Manchester, described the core discovery directly: "By continuously monitoring hormones over 24 hours, we were able to reveal a previously hidden pattern of nocturnal hormone bursts. This gives us a much clearer understanding of the disease and could ultimately help doctors detect it earlier and treat patients more effectively." That nighttime pattern is the crux of why standard testing misses so many cases: clinical blood draws essentially never happen while a patient is asleep, meaning an entire category of diagnostically relevant hormone activity has been structurally invisible to conventional testing all along, not because doctors were looking in the wrong place during the day, but because nobody was looking at all during the hours when some of the most telling activity was occurring.

Perhaps the more clinically unsettling finding is what happened even during daytime, single-sample-equivalent measurements. The study found that even among some of the most severe cases of the disease, aldosterone levels periodically dipped below the minimum thresholds typically used to diagnose the condition. That means a patient could genuinely have primary aldosteronism, get tested during one of those low-level windows, and receive a falsely reassuring normal result, remaining undiagnosed despite abnormal hormone production occurring at other points across the same day.

The detail that confirms the pattern is real, not noise

One of the study's more persuasive pieces of evidence concerns which patients showed the strongest nighttime hormone bursts. The pattern was particularly prominent in patients whose disease originated from a problem in just one adrenal gland rather than both, a distinction that matters for treatment since unilateral disease is often surgically curable, while bilateral disease is usually managed with medication instead. The researchers confirmed the connection was genuinely causal rather than coincidental by tracking what happened after surgery: the abnormal hormone bursts disappeared entirely following surgical removal of the affected adrenal gland, direct evidence that the bursts were being produced specifically by the diseased tissue rather than reflecting some unrelated, independent process.

What this means for how hypertension gets worked up

Professor Stafford Lightman, professor of medicine at the University of Bristol and inventor of the U-RHYTHM technology underlying this research, has spent years developing tools for capturing hormone dynamics that single time-point testing simply cannot see. This study represents a concrete clinical application of that broader research program, applied specifically to a condition affecting a meaningful share of the roughly one in three adults worldwide who have high blood pressure. Given that primary aldosteronism is potentially curable, particularly the unilateral cases treatable through surgery, missed diagnoses aren't a purely academic concern; they represent real patients living with a treatable underlying cause of their hypertension who instead get managed with standard blood pressure medications that don't address the actual driver of their condition.

What the study doesn't yet establish

The researchers themselves are careful about the limits of what a 60-patient proof-of-concept study can demonstrate. It does not yet show that wearable hormone monitoring should replace existing diagnostic tests entirely, or that routinely deploying this kind of device across the broader hypertensive population will measurably improve patient outcomes. Those are considerably larger claims requiring bigger, more diverse patient cohorts and direct outcome comparisons against standard care, the kind of evidence a single mechanistic study, however well-designed, isn't positioned to provide on its own.

Where this points next

What this research does convincingly establish is a genuine diagnostic blind spot in how one of the more common secondary causes of hypertension currently gets identified, and a specific, testable device-based approach for closing that gap. If larger follow-up studies confirm that continuous ambulatory hormone monitoring meaningfully improves detection rates without an unreasonable burden on patients or health systems, integrating this kind of monitoring into routine hypertension workups could become a genuine option for cases where standard testing keeps coming back inconclusive despite ongoing clinical suspicion. For a condition potentially driving high blood pressure in a significant fraction of the hundreds of millions of people living with hypertension worldwide, even modest improvements in detection accuracy could translate into a meaningful number of patients finally getting treatment aimed at the actual cause of their disease, rather than simply managing its downstream symptom.