Comparison of blood pressure measured at the arm, ankle and calf

The suitability of alternative sites for non-invasive blood pressure (NIBP) measurement was investigated in 100 awake healthy volunteers. The calf and the ankle were chosen for comparison with the arm, and the results analysed subjected to Bland-Altman analysis. Discomfort was graded using a Visual Analogue Scale. There was a poor agreement between the different sites with respect to systolic blood pressure: the agreement was closer for diastolic and mean measurements. The mean blood pressure calf measurement was on average 4 mmHg (95% limits of agreement -12 to 20), higher than the arm. The ankle was 8 mmHg higher (-8 to 24) than the arm. ANOVA demonstrated a statistically significant difference in the discomfort scores between the sites (p < 0.001). The calf demonstrated the highest discomfort score and the ankle the lowest. We suggest that the ankle should be considered in preference to the calf as an alternative site for NIBP measurement if use of an arm is undesirable or impossible.