Wearable health data, what it can tell you and what to bring to a doctor

What wearables measure well, and less well

A systematic review of 158 studies found that, in laboratory settings, consumer wearables measured steps and heart rate accurately, though accuracy varied between manufacturers and devices [1]. For energy expenditure, the calories you burn, no brand was accurate [1].

The most useful thing a wearable gives you is your own trend over time, measured the same way each day. A resting heart rate that drifts up over weeks, or a fall in activity after an illness, can be worth a conversation. Devices and their software are redesigned often, so a change after an update may reflect the device more than your body [1].

Wellness features and medical features

Most of what a wearable shows is a wellness feature, intended to encourage a healthy lifestyle and unrelated to diagnosing or treating disease, which regulators treat as low risk [2]. In the UK, an app that tells you that you have a condition, or gives you a personal percentage risk of having one, is a medical device and should carry a UKCA or CE mark, visible on its app store page [3].

The step count and a regulated heart rhythm feature on the same watch therefore carry different weight. Before acting on a health message, check which kind of feature produced it [3].

Irregular rhythm alerts

In a study of 419,297 people who wore a smartwatch, 0.52% received an irregular pulse notification over a median of 117 days [4]. Among those who then wore an ECG patch, atrial fibrillation was found in 34% [4]. An alert is a reason to be checked, and it is the later test that confirms or rules out a problem.

NICE advises that atrial fibrillation is diagnosed with a 12-lead ECG, and its committee chose this test to avoid relying on less accurate mobile and single-lead devices [5]. If the rhythm comes and goes, a doctor may suggest a monitor worn for 24 hours or longer [5].

If an alert comes with chest pain, severe breathlessness, fainting, or weakness of the face, arm or leg, call 999 in the UK or the local emergency number.

False alarms and false reassurance

A wearable can worry you without reason, and it can also reassure you when it should not. A normal reading on your wrist does not rule out a heart rhythm problem, because some rhythms come and go and a device checks only part of the time. NICE notes that monitoring for longer makes detection more accurate [5].

Symptoms matter more than the number. If you have palpitations, breathlessness, dizziness or chest discomfort, see a doctor whatever the device shows [5]. Before you rely on a health app, the MHRA suggests thinking about what you will do with the result and whether you will understand it [3].

Blood pressure and sleep readings

Blood pressure from a device without a cuff is not yet reliable enough for medical decisions. The European Society of Hypertension does not recommend cuffless devices for diagnosing or managing high blood pressure until questions about their accuracy are answered [6]. A doctor will confirm any concern with a cuff measurement before deciding anything.

Sleep stages are where trackers are least certain. Our sleep clinic has written a full guide to how accurate sleep trackers are, linked below, and a sleep consultation is the place to take a sleep problem that lasts.

What to bring to a doctor

A few weeks of data, with the context around it, helps a doctor far more than a single reading. Keep the device on the same wrist and wear it consistently, so the trend compares like with like.

• A screenshot or export of the trend over several weeks, with the dates of any change.
• The date and time of each alert, what you were doing and how you felt at the time.
• Any symptoms such as palpitations, breathlessness, dizziness or chest discomfort, which NICE lists as reasons to check the heart rhythm [5].
• Which feature produced the alert, and whether it carries a UKCA or CE mark [3].
• Your medicines, and any recent illness, travel or change in training that could explain the pattern.

How The Wellness can help

A telephone consultation lets you talk an alert or a changing trend through with a GP the same day, and decide together whether it needs a test. If it does, the doctor arranges it and explains the result with you, and if it does not, you leave with a clear sense of which readings are worth watching and which you can set aside. For sleep that has not been right for a while, a sleep consultation and assessment gives you an hour for a full assessment.

Every doctor is GMC registered. Our clinics are on Baker Street in Marylebone and Eccleston Street in Belgravia, and a doctor can come to your home or hotel in London.