Calf blood pressure measurement for detecting elevated arm blood pressure in hemodialysis patients

OBJECTIVE: To evaluate the relationship between standardized arm and calf blood pressure (BP) measurements obtained in the habitual posture of hemodialysis (HD) and to derive calf BP values corresponding to abnormal arm BP thresholds. METHODS: This cross-sectional study included 277 HD participants. Arm and calf BP were measured immediately before dialysis in the habitual HD posture. Linear regression estimated calf values corresponding to arm BP thresholds of 140/90 mmHg and 130/80 mmHg. Receiver operating characteristic (ROC)/Youden analysis identified optimal calf cutoffs. Cutoff-specific sensitivity, specificity, and area under the curve (AUC) were calculated, and agreement was assessed using Bland-Altman analysis. RESULTS: Participants were 55 ± 14 years old, and 64% were male. Mean arm and calf BP were 140 ± 24/83 ± 14 mmHg and 167 ± 29/92 ± 17 mmHg, respectively. Arm-calf correlations ranged from 0.72 to 0.74. Regression-derived calf values corresponding to arm BP 140/90 mmHg and 130/80 mmHg were 167/98 mmHg and 158/89 mmHg, respectively. ROC-optimized calf cutoffs were 171.5/96.7 mmHg for arm BP 140/90 mmHg and 162.2/91.2 mmHg for 130/80 mmHg. For combined SBP-or-DBP classification, the ROC-optimized cutoffs yielded sensitivity/specificity of 79.6%/76.6% and 83.7%/80.8%, with AUCs of 0.781 and 0.823, respectively. Mean calf-arm biases were +26.5 mmHg for SBP and +8.8 mmHg for DBP, with wide limits of agreement indicating substantial individual variability. CONCLUSION: In conclusion, when upper-arm BP measurement is not feasible in HD patients, ROC-derived calf BP cutoffs of approximately 170/100 mmHg and 160/90 mmHg may help identify contemporaneous arm BP thresholds of 140/90 mmHg and 130/80 mmHg, respectively. However, calf and arm BP are not interchangeable, and these cutoffs should be considered exploratory until externally validated.