A single high reading at a GP surgery does not, on its own, mean a person has hypertension. What actually converts a raised number into a diagnosis – and into a course of action – is a specific set of thresholds published by the National Institute for Health and Care Excellence (NICE) in guideline NG136. For a city trying to catch cardiovascular risk earlier, these thresholds matter as much as the screening programmes that generate the readings in the first place: they are the rule that decides who gets reassurance, who gets a repeat check, and who gets treatment.
This matters at population scale. London runs blood-pressure checks through GP surgeries, community pharmacies, workplace health events and NHS Health Checks, but every one of those touchpoints ultimately feeds into the same NICE decision tree. Understanding that tree explains why "early detection" is not just about testing more people – it is about applying a consistent, evidence-based cut-off once you have.
Why a clinic reading alone is not a diagnosis
NICE NG136 is explicit that a clinic blood-pressure reading of 140/90 mmHg or higher should not be treated as confirmed hypertension. Readings taken in a clinical setting are known to run higher than a person’s true average – the well-documented effect of nerves, a rushed appointment or an unfamiliar environment. Before a diagnosis is made, NICE requires confirmation with ambulatory blood pressure monitoring (ABPM), the preferred method, or home blood pressure monitoring (HBPM) where ABPM is not tolerated or available. Only once that confirmatory average is in hand does a person move from "raised reading" to a formal diagnosis with a defined stage.
The three diagnostic stages, and what happens at each
NG136 defines hypertension in three bands, each pairing a clinic figure with the corresponding ABPM/HBPM average – because the two settings are not measuring on the same scale.
| Stage | Clinic reading | ABPM/HBPM average | NICE-recommended response |
|---|---|---|---|
| Stage 1 | 140/90 mmHg or higher | 135/85 mmHg or higher | Lifestyle advice for everyone; drug treatment discussed for adults under 80 with existing cardiovascular disease, kidney disease, diabetes, organ damage, or a calculated 10-year cardiovascular risk of 10% or more |
| Stage 2 | 160/100 mmHg or higher | 150/95 mmHg or higher | Lifestyle advice plus drug treatment offered regardless of calculated risk score |
| Severe | Systolic 180 mmHg or higher, or diastolic 120 mmHg or higher | Not applicable – urgent pathway | Same-day assessment for signs of organ damage; if none are found, treatment starts immediately with bloods checked and blood pressure repeated within seven days |
People under 40 who reach either Stage 1 or Stage 2 are treated as a special case: NICE recommends they are considered for specialist evaluation to rule out a secondary, treatable cause of their high blood pressure, alongside a more detailed conversation about the long-term balance of treatment benefit and risk, given the decades of exposure ahead of them.
Why the two-scale system exists
The gap between the clinic figure and the ABPM/HBPM figure at every stage – 140/90 versus 135/85, 160/100 versus 150/95 – is not rounding. It is a deliberate correction for the fact that out-of-clinic readings tend to run a little lower once the effect of being examined is removed. Using a single number across both settings would either miss genuine cases (if the clinic threshold were applied to home readings) or diagnose healthy people (if the lower out-of-clinic threshold were applied inside a clinic room). Building both numbers into the guideline is what lets a pharmacy blood-pressure check, a GP reading and a week of home monitoring all point toward the same underlying diagnosis.
What this means below the diagnostic line
NICE is also specific about people who do not meet either threshold. Someone with a raised reading that falls short of Stage 1 is not simply dismissed – the guideline recommends they still receive brief healthy-living advice, and in practice many services offer a repeat check at a defined interval rather than waiting for the next opportunistic visit. That distinction matters for a screening system trying to work at scale: capacity is finite, and a threshold-based response – reassurance and advice for some, confirmatory monitoring for others, urgent same-day pathways for a smaller number still – is what allows a fixed number of GP appointments and pharmacy slots to be allocated according to actual risk rather than treating every raised number identically.
The takeaway for population screening
Early detection only works if the systems doing the detecting agree on what they are detecting. NG136’s three-stage structure – with its paired clinic and out-of-clinic thresholds, its urgent pathway for severe readings, and its extra scrutiny for younger patients – is the mechanism that turns a citywide patchwork of blood-pressure checks into a single, evidence-based diagnostic standard. Whoever takes the reading, and wherever it is taken, the same numbers decide what happens next.