Prevalence and Factors Associated with Borderline or Abnormal Ankle–Brachial Index Findings among Hospitalised Adults in Singapore: A Cross-Sectional Study

Abstract Background Peripheral arterial disease (PAD) is frequently under-recognised because individuals may be asymptomatic or present with atypical symptoms. Although an ankle–brachial index (ABI) < 0.90 is considered abnormal and suggestive of PAD, borderline ABI values (0.91–0.99) may also identify individuals at increased risk of PAD and cardiovascular disease. Evidence on borderline ABI among general hospitalised adults in Singapore remains limited. Methods A cross-sectional study using convenience sampling was conducted among adults aged ≥ 50 years without known PAD who were admitted to Internal Medicine wards at a tertiary hospital in Singapore between February 2024 and April 2025. Demographic and clinical characteristics and bilateral ABI measurements were collected. ABI was classified as abnormal (< 0.90), borderline (0.91–0.99), or normal (1.00–1.40). Characteristics were compared across ABI groups,and multivariable linear regression was used to identify factors associated with the lowest ABI per participant. A linear mixed-effects model accounted for bilateral ABI measurements. Results Among 122 participants, 83 (68.0%) had normal ABI in both limbs, 29 (23.8%) had at least one borderline ABI without an abnormal ABI, and 10 (8.2%) had at least one abnormal ABI. Overall, 39 (32.0%) had at least one borderline or abnormal ABI finding. Routine lower-limb clinical findings were predominantly normal among affected limbs. In multivariable analysis, increasing age (B = − 0.002, p = 0.018) and higher BMI (B = − 0.005, p = 0.006) were independently associated with lower ABI values. Participants with diabetes had higher adjusted ABI values than those without diabetes (p = 0.027). These associations remained statistically significant in the bilateral mixed-effects model (age, p = 0.030; BMI, p = 0.002; diabetes mellitus, p = 0.033). Conclusion Borderline or abnormal ABI findings were identified in approximately one-third of hospitalised adults aged ≥ 50 years without previously diagnosed PAD, despite predominantly normal bedside vascular findings. Identifying individuals with borderline ABI may provide an opportunity for earlier cardiovascular risk assessment and follow-up before progression to abnormal ABI or clinically recognised PAD. Larger multicentre studies are needed to confirm these findings and evaluate targeted vascular assessment strategies and their potential to improve clinical outcomes.