What causes 24 hour errors

The magazine for medical professionals

Is there a white coat effect?


© Jochen Tack
This is how it is correct: The patient sits quietly and leaned, the arm is slightly bent and the cuff is at heart level.

The Italian doctor Riva-Rocci, who invented the modern form of blood pressure measurement in 1896, believed he observed that a patient's blood pressure rose when he was present during the measurement. This was initially ridiculed, but now systematic studies have shown that the presence of a doctor when measuring blood pressure can cause the systolic value to rise by up to 22 mmHg. For the other members of the practice team, the effect is only half as great. This form of division of labor makes sense not only from an organizational point of view, but also from a medical point of view. For a correct measurement it is essential to observe the following points:

  • Calm environment. The patient should rest for five minutes before taking the measurement.
  • Relaxed sitting during the measurement (chair with backrest). Put your arm down and bend it slightly.
  • Choose the correct cuff size and measure on the bare arm.
  • Place the cuff in the middle of the upper arm, must be at heart level for the measurement.
  • The inflation takes place quickly up to a pressure height of approx. 30 mmHg above the disappearance of the pulse on the wrist.
  • Slow release of pressure (2 mmHg / s) while listening to Korotkoff noises. This is often forgotten when there is a rush in everyday practice. However, the measured values ​​can be falsified if the pressure is drained too quickly.
  • Read the values ​​to an accuracy of 2 mmHg.
  • Repeat measurement on the same arm after 30 seconds at the earliest.
Influencing factor Effect on systol. value Effect on diastole. value
Urge to stool or urinate +27 mmHg +22 mmHg
White coat effect +22 mmHg +14 mmHg
Speak+17 mmHg+13 mmHg
Smoke+10 mmHg+8 mmHg
drink coffee+10 mmHg+7 mmHg
Acute cold (drafts)+11 mmHg+8 mmHg
Lack of back supportup to +8 mmHg+ 6-10 mmHg
Cuff too narrow- 8 mmHg+8 mmHg
Legs crossed+ or -, variable+ or -, variable
Emotional burden+, variable+, variable
Source: Der Hausarzt 15/09, pp. 54, 55

The 24-hour measurement

Long-term blood pressure measurement enables a very precise measurement of blood pressure. For example, the day-night rhythm of blood pressure can be checked with such a 24-hour measurement. If the patient is already being treated with medication, this can be used to control how effective the treatment is.

For long-term measurements, patients are given a measuring device that they wear on their body for 24 hours. This device measures and records blood pressure every 15 minutes during the day and every half hour at night. The patients add information about daily activities, medication intake, sleep quality, etc.

Outpatient self-measurements by patients should be treated with caution. Incorrect measurement technology and unreliable devices are the decisive sources of error here. The measurement in practice can thus be supplemented, but not replaced.