How often should testing be repeated?
Set the interval from what was found and what is being changed, not from the calendar.
The four situations
| Situation | Typical interval | Why |
|---|---|---|
| Normal study, risk group, nothing being changed | About a year | The value is the trend; annual keeps it comparable without over-testing |
| Borderline result | Weeks, under controlled conditions | Borderline values are frequently artifacts of preparation, sleep or coaching. Repeat before concluding |
| Abnormal result, something being actively changed | Three to six months for metabolic measures | Long enough for a real change, short enough to correct course |
| Abnormal structural vascular finding | Longer, and guided by the clinical plan | Structural change is slower than metabolic change |
Why calendar-driven repeats waste the measurement
The point of repeating is comparison, and comparison only works when something has had a chance to move. Re-measuring resting energy expenditure six weeks into a nutrition plan tells you almost nothing; re-measuring at four months tells you whether the plan is working. Conversely, waiting a full year to recheck a borderline ankle-brachial index in a smoker with worsening claudication is too long.
The conditions have to match
A repeat measured under different conditions is not a comparison. Same fasting state, same time of day, no caffeine or nicotine either time, same instrument, same technique, same posture and the same rest period. If the first was taken after a poor night’s sleep, note it and take that into account rather than pretending the two are equivalent.
This is why the conditions are recorded as part of the result. Why acquisition conditions matter.
What changes fastest
- Within weeks to months: triglycerides, fasting glucose and insulin, measured metabolic rate, body composition, heart rate variability.
- Within months to a year: waist circumference, hemoglobin A1c, inflammatory markers, endothelial markers, sudomotor conductance where a driver has been corrected.
- Slowly, if at all: established arterial stiffness and structural arterial narrowing.
That ordering is also the argument for measuring early: the things that respond fastest are the ones upstream of the things that barely respond at all.
Related reading
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, medical director of Measura. Last reviewed .