A new study has uncovered hidden hormone surges that may explain why primary aldosteronism, a hormone disorder that affects up to one in five people with high blood pressure, often goes undetected by standard blood tests. Researchers from the University of Bristol, University of Manchester, University of Bergen, and institutions in Stockholm and Athens used a wearable device to continuously monitor hormone levels in patients living at home. This device, called U-RHYTHM and developed at the University of Bristol, measured hormone levels every 20 minutes over a 24-hour period, revealing patterns that traditional testing methods might miss. The study found that patients with primary aldosteronism experience sudden bursts of hormone production both during the day and at night. These nighttime surges are particularly important because routine blood tests are rarely performed during sleep. The hormone spikes were more pronounced in patients with a problem affecting only one adrenal gland rather than both. When the affected adrenal gland was surgically removed, the unusual hormone patterns disappeared, reinforcing the link between these surges and the disease. Researchers suggest that current diagnostic methods may miss some cases because aldosterone levels, a hormone that regulates salt and water balance in the body, do not remain consistently high. Even in severe cases, hormone levels sometimes fall below the minimum thresholds used for diagnosis. As a result, a single blood test might capture a time when hormone levels appear normal, leading to a missed diagnosis. Study co-lead author Dr. Thomas Upton highlighted the importance of diagnosing primary aldosteronism earlier, as it is a significant cause of high blood pressure and could affect millions in the UK. The findings suggest that future diagnosis may shift from single-time-point blood tests to tracking hormone rhythms over time, especially the overnight patterns that seem to hold key clues to the disease. The research was supported by several organizations, including EU Horizon 2020, the Trond Mohn Foundation, and the UKRI Biotechnology and Biological Sciences Research Council. It aligns with the University of Bristol's focus on understanding and preventing cardiovascular disease and supports efforts to identify people with hypertension and other cardiovascular risks earlier.