Digital biomarkers for metabolic health
The one domain where digital measurement replaced the conventional endpoint rather than merely supplementing it.
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Metabolic health is the domain where digital measurement has already replaced the conventional endpoint rather than merely supplementing it. Continuous glucose monitoring produces a reading every few minutes for weeks at a time, and the measures derived from that stream now sit alongside glycated haemoglobin in guidelines, in trials and in routine care.
The reason is that a single laboratory value and a continuous trace answer different questions. Glycated haemoglobin summarises average exposure over months and says nothing about how that average was reached. Two people with identical values can have entirely different days, one stable and one swinging between highs and lows, and only the second is at immediate risk. Time in range, time below range and glycaemic variability exist to describe that distinction.
This category also holds the measures that connect glucose to behaviour, including energy expenditure and the activity measures that shape metabolic outcomes. That connection is the practical value of digital metabolic measurement: the same recording period contains both the exposure and the behaviour that produced it, which is something no clinic visit can capture.
Metabolic health measures in this library
How these measures are used
Time in range is the most used digital endpoint in registered clinical trials in this library, and time below range is close behind. Together they appear as primary endpoints in a substantial share of the trials that use them, which is unusual and reflects an international consensus process that defined targets explicitly so they could function as endpoints.
In practice a metabolic study reports the range measures as a family rather than in isolation. Time in range alone can be improved by a treatment that also increases hypoglycaemia, which is why time below range is reported alongside it as a safety counterweight. Variability adds a third dimension that neither range measure captures.
Beyond diabetes trials, these measures are used in nutrition and behaviour research, and in studies of populations without diabetes where glucose response is an outcome. Patient reported instruments covering diabetes distress and treatment satisfaction are commonly paired with them, since a regimen that improves numbers while increasing burden is not straightforwardly a success.
What the evidence supports today
This is the strongest evidence base in the library. The 2019 international consensus on time in range set explicit clinical targets and the metric has been validated against the long term outcome data that established glycated haemoglobin as a surrogate, which is the step most digital measures never reach. Professional society standards of care now include continuous glucose monitoring metrics directly.
Sensor accuracy is well characterised and continues to improve, with the important caveat that accuracy is lowest in the hypoglycaemic range, which is precisely where time below range operates. Small absolute errors there translate into large proportional ones, so hypoglycaemia estimates carry more uncertainty than the headline range figure suggests.
Outside glucose, the evidence thins quickly. Energy expenditure estimated from wearables is useful for relative comparison within a person but is not accurate enough in absolute terms to support clinical claims, and studies that treat it as a calibrated measurement rather than an index tend to overreach.
Common questions
Does time in range replace glycated haemoglobin?
It does not replace it, but it is no longer treated as secondary to it. Guidelines now recommend reporting both, because they capture different things: glycated haemoglobin summarises average exposure over months, while time in range describes the pattern of the days that produced that average, including the lows an average conceals.
What is the standard target for time in range?
International consensus recommends more than seventy percent of the day within the target glucose range for most adults with type 1 or type 2 diabetes, with different and more conservative targets for older or high risk groups and for pregnancy. Targets are set by consensus, so they are periodically revised.
Why is time below range reported separately?
Because it functions as a safety measure. A treatment can raise time in range while also pushing more of the day into hypoglycaemia, which would look like success on the headline metric alone. Reporting both prevents that, and hypoglycaemia carries acute risk that a range percentage does not convey.
Are these measures useful in people without diabetes?
They are used in nutrition and physiology research, where continuous glucose data reveals responses to meals and activity that periodic testing misses. The clinical targets defined for diabetes do not transfer to that setting, and interpreting normal variation as a problem is a known pitfall in consumer applications of this technology.
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