How to Take Blood Pressure: A Medical Assistant Guide

Equipment You Need

Two pieces of equipment handle every manual blood pressure reading: a sphygmomanometer and a stethoscope.

The sphygmomanometer has three parts that matter. The cuff itself, which contains an inflatable bladder. The manometer, which displays the pressure reading — either a mercury column, an aneroid gauge, or a digital display. And the bulb with a valve that lets you inflate and control deflation speed.

The stethoscope bell or diaphragm picks up the sounds you need to identify systolic and diastolic pressure. Most clinicians use the diaphragm for blood pressure. Either works.

Cuff sizing is one of the most tested and most ignored aspects of the procedure. The bladder inside the cuff should encircle at least 80% of the arm circumference. A cuff that is too small gives a falsely high reading. A cuff that is too large gives a falsely low reading. Standard adult, large adult, thigh, pediatric, and infant cuffs exist for a reason. Measure the arm if you are unsure.

Manual Technique: Step by Step

Position the patient correctly before you start. The patient should be seated with their back supported, feet flat on the floor, and arm resting at heart level. They should have been sitting quietly for at least five minutes. No caffeine, tobacco, or exercise for 30 minutes prior. These are not minor details — they change readings.

1. Expose the arm. Roll up the sleeve or have the patient remove it. Do not take blood pressure over clothing. This introduces error every time.
2. Position the cuff. Place the lower edge of the cuff about 1 inch (2.5 cm) above the antecubital fossa (the crease of the elbow). The artery marker on the cuff should align over the brachial artery.
3. Palpate the brachial artery. Use your fingertips to feel the brachial artery pulse on the medial aspect of the antecubital fossa. This tells you where to place your stethoscope.
4. Estimate systolic by palpation. With the stethoscope off, inflate the cuff while palpating the radial pulse. Note the pressure at which the radial pulse disappears. That is your estimated systolic. Deflate the cuff completely.
5. Inflate to 30 mmHg above estimated systolic. Place the stethoscope over the brachial artery. Inflate the cuff 30 mmHg above the estimated systolic pressure you just determined. This ensures you do not miss an auscultatory gap.
6. Deflate at 2 to 3 mmHg per second. Open the valve slowly and steadily. Too fast and you miss the true reading. Too slow and venous congestion builds up, causing discomfort and inaccuracy.
7. Listen for Korotkoff sounds. The first sound you hear is Phase I — this is your systolic reading. The sounds continue through several phases and eventually disappear. The pressure at which sound disappears completely is Phase V — your diastolic reading.
8. Record both values. Document systolic over diastolic (e.g., 122/78), the arm used, the patient position, and the time.

Korotkoff Sounds

These five phases get tested on both the CMA and RMA exams. Know all of them.

• Phase I: The first clear tapping sounds. This is systolic pressure.
• Phase II: Softer, swishing or murmur sounds.
• Phase III: Sounds become sharper and louder again.
• Phase IV: Sounds become muffled and softer. In some patients, especially children and pregnant women, this is used as diastolic.
• Phase V: Sounds disappear completely. Standard diastolic reading for most adults.

The auscultatory gap is a period of silence that can occur between Phase I and Phase III, usually in patients with hypertension or arteriosclerosis. If you did not inflate high enough, you might start listening during this gap and record a falsely low systolic. That is why you always inflate 30 mmHg above estimated systolic.

Normal Ranges and Classifications

The American Heart Association classification system is the standard for exam purposes:

• Normal: Less than 120/80 mmHg
• Elevated: Systolic 120–129 and diastolic less than 80
• Hypertension Stage 1: Systolic 130–139 or diastolic 80–89
• Hypertension Stage 2: Systolic 140 or higher, or diastolic 90 or higher
• Hypertensive Crisis: Systolic over 180 and/or diastolic over 120 — requires immediate medical attention

The old term "prehypertension" covered 120–139/80–89. You may still see this term in older study materials and on some exams. The current terms split that range into "elevated" and "Stage 1 hypertension."

Automated vs Manual Blood Pressure

Automated devices use oscillometry — they detect oscillations in the arterial wall rather than listening for Korotkoff sounds. They are faster and do not require the same level of technique. Most outpatient offices rely heavily on automated devices for routine readings.

Manual technique remains important for several reasons. Automated machines can give inaccurate results in patients with arrhythmias, peripheral vascular disease, or excessive arm movement. Some situations require palpation-only technique when auscultation is not possible. And the CMA and RMA exams test manual technique, so you need to know it.

When using automated devices, still follow patient prep guidelines. Position still matters. Cuff sizing still matters. A badly positioned automated cuff gives a bad reading just like a manual one.

Common Errors

These mistakes lead to inaccurate readings and are frequently tested:

• Wrong cuff size: Too small gives falsely high; too large gives falsely low.
• Cuff over clothing: Clothing beneath the cuff interferes with transmission and accuracy. Always apply to bare skin.
• Patient talking or moving: This can raise systolic pressure by 10–40 mmHg. No talking during measurement.
• Arm not at heart level: Arm below heart level gives falsely high readings; arm above gives falsely low.
• Deflating too fast: Missing the sounds means inaccurate readings.
• Not waiting between readings: Allow at least 1 to 2 minutes between repeat measurements to let venous congestion resolve.
• Not palpating to estimate systolic first: Risks missing an auscultatory gap.
• Recording before full deflation: Causes errors in diastolic values.

Orthostatic Blood Pressure

Orthostatic (postural) blood pressure checks evaluate whether a patient has orthostatic hypotension — a significant drop in BP when moving from lying to standing. This is common in elderly patients, those on certain medications, and patients with dehydration or autonomic dysfunction.

The procedure: Take a baseline reading with the patient supine after 5 minutes of lying still. Then have the patient sit up and take another reading immediately. Then have them stand and take a third reading within 1 to 3 minutes of standing.

A positive orthostatic test (orthostatic hypotension) is defined as a drop of 20 mmHg or more in systolic, or 10 mmHg or more in diastolic, when moving from lying to standing. Symptoms like dizziness or near-fainting confirm the finding. Report positive results to the physician immediately.

Practice Questions