Upper arm NIBP measurements were the most accurate in the obese population, while alternative sites such as the forearm and ankle demonstrated inconsistent reliability and were prone to overestimation.
Ankle systolic blood pressure showed the greatest deviation from control measurements among all sites tested.
Significant agreement for mean arterial pressure was identified at the upper arm site, enabling derivation of a correction formula with high reliability.
Forearm and ankle blood pressure measurements demonstrated wider limits of agreement and were prone to overestimation compared to upper arm measurements.
The study enrolled 50 obese participants aged 20–60 years with BMI 35–40 kg/m² at a provincial tertiary hospital in South Africa.
Correction formulas derived from regression analyses can enhance NIBP accuracy but were noted to be potentially cumbersome for routine clinical use.
This research suggests that measuring blood pressure in obese individuals presents real challenges, and that where you place the cuff matters significantly. In a study of 50 obese adults in South Africa, researchers compared blood pressure readings taken at the upper arm, forearm, and ankle against a continuous reference measurement taken from the opposite hand using a device called VitalStream. They found that ankle measurements were the least reliable, overestimating systolic (top number) blood pressure by an average of more than 14 mmHg — a clinically meaningful difference that could affect medical decisions. Forearm readings also tended to overestimate blood pressure and showed inconsistent results. The upper arm remained the most accurate site for blood pressure measurement even in obese individuals, particularly for mean arterial pressure, where a statistically reliable correction formula could be developed. The researchers used Bland-Altman plots — a standard method for comparing two measurement techniques — to quantify how much each alternative site deviated from the reference standard. While mathematical correction formulas could theoretically improve accuracy at alternative sites, the authors noted these would be impractical for everyday clinical settings. This research suggests that healthcare providers should be cautious about relying on forearm or ankle blood pressure readings in obese patients, as these alternative sites may systematically overestimate blood pressure and lead to incorrect assessments. The findings reinforce using the upper arm as the primary site and highlight the need for appropriately sized cuffs. The authors call for future research into specially shaped cuffs designed for the conical upper arms common in obese individuals, which may help improve measurement accuracy at the standard site.
Van Dyk L, Mdzinwa N. (2026). Agreement between various non-invasive blood pressure measurement sites in the obese population using the VitalStream system as control.. South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde. https://doi.org/10.7196/SAMJ.2026.v116i5.3341