Daytime average over at least 14 measurements, with lower thresholds
Expansion
Thresholds
| Clinic | Ambulatory daytime average or home | |
|---|---|---|
| Stage 1 hypertension | 140/90 | 135/85 |
| Stage 2 hypertension | 160/100 | 150/95 |
| Severe | 180/120 |
Technique: at least two measurements per hour during waking hours, with the average of at least 14 measurements used. Home monitoring uses two readings, twice daily, for at least 4 days and ideally 7, discarding the first day.
Why it is used: clinic readings are confounded by the white coat effect, and a single clinic reading correlates poorly with cardiovascular risk. Ambulatory monitoring predicts outcome better than any clinic measurement, and it avoids treating people who do not need it.
The four patterns
- Sustained hypertension: high in clinic and out
- White coat hypertension: high in clinic, normal out. Prevalence around 20 per cent. It carries some increased risk and warrants follow-up, but usually not treatment
- Masked hypertension: normal in clinic, high out. Carries risk comparable to sustained hypertension and is missed entirely without ambulatory monitoring
- Normotension
Nocturnal dipping: blood pressure normally falls by 10 to 20 per cent overnight. Non-dipping or reverse dipping is associated with obstructive sleep apnoea, chronic kidney disease, diabetic autonomic neuropathy and worse cardiovascular outcomes.
Where it does not apply: severe hypertension of 180/120 or above with signs of end organ damage requires same day assessment and treatment, not a monitoring period. Atrial fibrillation degrades the accuracy of oscillometric devices, and monitoring is poorly tolerated by some patients, for whom home readings are the alternative.