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Frequency of spontaneous fist clenching during routine blood pressure measurements and its effect on measurement accuracy

BackgroundGuidelines for office blood pressure reading techniques do not warn us about the possibility that patients may clench their fist during cuff-inflation. It is unknown how often patients do this, and what effect it has on measured blood pressure readings. Design and MethodsWe registered double blood pressure readings in 150 outpatient clinic subjects, who were not given specific instructions as to how to hold their hand during the procedure. If they clenched their fist during the first reading, they were asked to relax their hand during the second reading, and vice versa. Double readings with a relaxed hand on both occasions were registered in 100 matched control patients as well. ResultsTwenty-two of 150 patients (15%) spontaneously made a fist during the first reading. No systematic effect (lower or higher blood pressure) from making a fist was observed, but individual effects were often marked, as evidenced by the median absolute differences (regardless of ‘+’ or ‘−’ sign) between the duplicate readings: 5 (range 0–31) versus 3 (0–18) mmHg for systolic blood pressure, and 4 (0–22) versus 2 (0–16) mmHg for diastolic blood pressure in the study group versus the control group, respectively (P  ≤ 0.05). A different hypertension classification occurred twice as often when a fist was made during one of the two blood pressure readings than with two fistless readings (23 versus 12%, P  = 0.04). ConclusionAbout one out of every seven patients makes a fist during blood pressure taking. This can seriously affect measurement accuracy, and doubles the risk of misclassification of hypertension.