How High Blood Pressure Is Diagnosed

High blood pressure is never diagnosed from a single reading. Blood pressure varies from minute to minute, and readings in a doctor's office are often higher than at home. Guidelines therefore require repeated measurements — ideally confirmed outside the office.

Step 1: office readings

The doctor or nurse takes at least two readings on at least two occasions, with proper technique (seated, rested, correct cuff). An average of 130/80 or higher meets the US definition of hypertension; 140/90 or higher the European one. A reading above 180/120 with signs of organ damage is treated as an emergency right away.

Step 2: confirm outside the office

• Home blood pressure monitoring: two readings morning and evening for about a week. Hypertension if the average is 130/80 or higher. See How to Check Your Blood Pressure at Home.
• 24-hour ambulatory monitoring (ABPM): a cuff measures automatically every 15–30 minutes during the day and night. It also shows whether blood pressure falls normally at night ("dipping").

White-coat and masked hypertension

White-coat hypertension affects up to a third of people with high office readings; masked hypertension — common in smokers, people under stress and those with diabetes — is missed without home or 24-hour readings.

Step 3: tests after the diagnosis

Once hypertension is confirmed, doctors look for causes and for damage it may already have done:

• Blood tests: kidney function (creatinine, eGFR), sodium, potassium, blood sugar or HbA1c, cholesterol, thyroid hormone
• Urine test for protein (albumin-to-creatinine ratio)
• ECG, sometimes an echocardiogram
• An estimate of 10-year cardiovascular risk, which helps decide when medication is needed

Secondary hypertension

In about 5–10% of people, a specific cause is found — for example primary aldosteronism (a hormone-producing adrenal gland), kidney disease, narrowing of the kidney arteries, sleep apnea, thyroid disorders or medications. Clues are hypertension at a young age, sudden onset, very high or treatment-resistant readings, or low potassium.

Next steps: lifestyle measures and medication options.