Sixty people with high blood pressure spent a full day and night going about ordinary life with a sampler the size of a cellphone clipped at the waist. Every 20 minutes, without a needle stick, it drew fluid from just beneath the skin. What it captured was the pattern a single clinic blood draw is built to miss: repeated bursts of a blood pressure hormone, concentrated in the hours the patients were asleep.
The findings, published Aug. 26 in Science Translational Medicine, concern primary aldosteronism, a disorder in which the adrenal glands overproduce aldosterone, the hormone that governs how the body handles salt and water. It is the most common endocrine cause of secondary high blood pressure, and it is often missed. Investigators at the University of Bergen in Norway led the work, with collaborators at the University of Bristol and the University of Manchester in the United Kingdom. Researchers recruited patients in Bristol, Bergen, Stockholm, and Athens.
Sixty Patients, One Sampler, and a Reading Every 20 Minutes
The device, called U-RHYTHM, was developed at the University of Bristol and pulls microdialysis samples from tissue just under the skin rather than from blood. That distinction matters: it lets sampling continue through sleep, work and meals without waking anyone or requiring a hospital bed. Earlier work using the same technology mapped 24-hour adrenal steroid rhythms in healthy volunteers and established what a normal profile looks like.
This time, the team turned it on patients with a confirmed diagnosis. Computational analysis tracked aldosterone alongside two related steroids, 18-hydroxycortisol and 18-oxocortisol. Rather than the flat, persistently elevated hormone levels a textbook might predict, the profiles showed something closer to a series of spikes. Bursts occurred during the day as well, but the dysregulation was most pronounced overnight, even as a day-night rhythm remained intact.
The spikes were most prominent in patients whose disease came from a problem in a single adrenal gland rather than both. That subtype is the one most likely to be cured by surgery, which makes it the subtype clinicians most want to identify early.
Why a Normal Blood Test Does Not Rule the Condition Out
The most consequential detail in the paper is not the spikes. It is the troughs. Researchers reported that even among some of the most severe cases in the group, hormone levels at certain points in the day dropped below the minimum thresholds used to diagnose the condition.
In plain terms, a patient with unmistakable disease could walk into a clinic, get blood drawn at 10 a.m., and produce a result that looks unremarkable. Standard screening relies on a single measurement of aldosterone and renin, taken in the morning during business hours. If aldosterone output is episodic rather than constant, the timing of that single draw matters a great deal.
"Due to the way hormones change during the day and the current complexity of the diagnostic process, diagnosis is often delayed or never made at all," said study co-lead author Dr. Thomas Upton, a clinical research fellow at the University of Bristol and senior clinical fellow at Bristol Hospitals NHS Foundation Trust.
The Bursts Disappeared After Surgery
The strongest evidence linking the pattern to the disease came afterward. In patients who had the affected adrenal gland surgically removed, the abnormal hormone profiles went away. That before-and-after comparison is what separates this from a curious observation: the spikes tracked the diseased tissue.
Study senior author Dr. Eder Zavala, a UKRI Future Leader Fellow at the University of Manchester, said continuous monitoring revealed "a previously hidden pattern of nocturnal hormone bursts" and could eventually help doctors detect the disorder earlier and treat patients more effectively.
Important limits apply. This was a proof-of-concept investigation in 60 patients across four cities, not a diagnostic trial, and it did not test whether dynamic monitoring finds cases that current screening misses. U-RHYTHM is a research instrument, not a consumer wearable or an approved home diagnostic. Nothing in the paper changes current screening guidance.
Why This Matters for American Patients
Nearly half of U.S. adults have high blood pressure, according to the Centers for Disease Control and Prevention, and about 1 in 6 of them does not know it. Primary aldosteronism accounts for a meaningful slice of that burden. The Endocrine Society estimates it affects 5% to 14% of hypertension patients in primary care and up to 30% at referral centers, yet most people with hypertension never receive the blood test.
That gap is why the society's clinical practice guideline suggests screening all adults with hypertension, a conditional recommendation the panel graded on low-certainty evidence. Patients who are found to have it have options ordinary hypertension patients do not: targeted medication, or, in one-sided disease, surgery that can resolve the problem outright.
Prof. Stafford Lightman, professor of medicine at the University of Bristol and inventor of the U-RHYTHM technology, said the findings suggest clinicians may need to rethink how they look for the disorder, moving away from single time-point blood tests and toward tracking hormone rhythms over time. He added that further research is needed to define the best clinical pathways.
For now, the practical takeaway is narrower than the headline finding. Anyone with high blood pressure that resists medication, appears at a young age, or comes with low potassium has reason to ask a clinician specifically about primary aldosteronism testing. A single normal result does not close the question.
Key Questions Answered
What did the study actually find?
In 60 patients with primary aldosteronism, a wearable sampler recorded repeated bursts of aldosterone production, with the dysregulation most pronounced during sleep. Hormone levels were episodic rather than persistently high.
Why would that cause missed diagnoses?
Screening depends on a single morning blood draw. If output rises and falls in spikes, that one sample can land in a trough. Researchers reported levels dipping below diagnostic cutoffs even in severe cases.
Is the device available to patients?
No. U-RHYTHM is a research tool used in this study, not an approved home diagnostic or a consumer wearable.
Does this change how doctors should test for the condition?
Not yet. This was a proof-of-concept study, and the authors said further research is needed to define clinical pathways.
Who should ask their doctor about primary aldosteronism?
People whose blood pressure stays high on multiple medications, who develop hypertension young, or who have low potassium. Endocrine Society guidance suggests considering screening in all adults with hypertension.
