Inter-observer reliability and anatomical landmarks for arm circumference to determine cuff size for blood pressure measurement

Accurate arm circumference (AC) measurement is required for accurate blood pressure (BP) readings. Standards stipulate measuring arm circumference at the midpoint between the acromion process (AP) and the olecranon process. However, which part of the AP to use is not stipulated. Furthermore, BP is measured sitting but arm circumference is measured standing. We sought to understand how landmarking during AC measurement and body position affect cuff size selection. Two variations in measurement procedure were studied. First, AC was measured at the top of the acromion (TOA) and compared to the spine of the acromion (SOA). Second, standing versus seated measurements using each landmark were compared. AC was measured to the nearest 0.1 cm at the mid-point of the upper arm by two independent observers, blinded from each other's measurements. In 51 participants, the mean (±SD) mid-AC measurement using the anchoring landmarks TOA and SOA in the standing position were 32.4 cm (±6.18) and 32.1 cm (±6.07), respectively (mean difference of 0.3 cm). In the seated position, mean arm circumference was 32.2 (±6.10) using TOA and 31.1 (±6.03) using SOA (mean difference 1.1 cm). Kappa agreement for cuff selection in the standing position between TOA and SOA was 0.94 (p < 0.001). The landmark on the acromion process can change the cuff selection in a small percentage of cases. The overall impact of this landmark selection is small. However, standardizing landmark selection and body position for AC measurement could further reduce variability in cuff size selection during BP measurement and validation studies.