Normal Blood Pressure for an 18-Year-Old
For an 18-year-old weighing 55 kg, normal blood pressure is defined as less than 120 mm Hg systolic AND less than 80 mm Hg diastolic. 1
Blood Pressure Classification for Adults 18 Years and Older
The Joint National Committee (JNC 7) guidelines establish the following categories that apply to all adults aged 18 years and older, regardless of weight: 1
- Normal BP: <120 mm Hg systolic AND <80 mm Hg diastolic 1
- Prehypertension: 120-139 mm Hg systolic OR 80-89 mm Hg diastolic 1
- Stage 1 Hypertension: 140-159 mm Hg systolic OR 90-99 mm Hg diastolic 1
- Stage 2 Hypertension: ≥160 mm Hg systolic OR ≥100 mm Hg diastolic 1
Important Clinical Context
Weight is not a factor in defining normal blood pressure ranges for adults. 1 The classification system applies uniformly to all adults 18 years and older based solely on measured blood pressure values, not body weight or body mass index. 1
The classification requires proper measurement technique: blood pressure should be based on the average of 2 or more properly measured, seated readings on each of 2 or more office visits. 1
Cardiovascular Risk Considerations
Even blood pressure in the "prehypertensive" range (120-139/80-89 mm Hg) carries increased cardiovascular risk. 1 Data from over 1 million individuals demonstrate that cardiovascular mortality increases progressively and linearly starting from blood pressure levels as low as 115/75 mm Hg. 1
For every 20 mm Hg systolic or 10 mm Hg diastolic increase above 115/75 mm Hg, there is a doubling of mortality from both ischemic heart disease and stroke. 1
Common Pitfalls to Avoid
Do not assume that body weight modifies the definition of normal blood pressure in adults. 1 While obesity is associated with higher blood pressure and increased cardiovascular risk, the threshold values for normal blood pressure remain constant across all body weights in adults 18 years and older. 2
Do not rely on a single blood pressure measurement. 1 Proper classification requires multiple measurements on separate occasions to account for normal blood pressure variability and to exclude white-coat hypertension. 1
Do not dismiss blood pressure in the 120-139/80-89 mm Hg range as "normal." 1 This prehypertensive range warrants lifestyle modifications to prevent progression to hypertension, as individuals in this range have twice the risk of developing hypertension compared to those with lower values. 1