Optimizing ankle-brachial index measurement for peripheral arterial disease screening in mobile clinics

Optimizing ankle-brachial index measurement for peripheral arterial disease screening in mobile clinics Shahida N. Balaparya, EdD, MBA, RVT,a Rosemary G. Cobb, BA,b Jaeyoung Lee, BS,b Jessica P. Simons, MD, MPH,a Douglas W. Jones, MD, MS,a Andres Schanzer, MD,a and Tammy T. Nguyen, MD, PhD,a,c Worcester, MA ABSTRACT Objective: Multidisciplinary mobile clinics (MMCs) provide a robust venue to provide health care access and peripheral arterial disease (PAD) screening to underserved populations. The ankle-brachial index (ABI) can facilitate PAD diagnosis; however, traditional supine ABI measurements may be challenging technically in a mobile outreach clinic with limited infrastructure, whereas seated ABI offers technical ease. In this study, the usefulness and feasibility of performing supine ABI, seated ABI, and seated ABI with a calculation to account for seated hydrostatic pressure (seated-adjusted ABI) were compared in a mobile outreach setting. Methods: Prospective data were collected from patients at five independent MMCs focused on diabetic foot and PAD screening with ABI for underserved communities. Three techniques were used to measure the ABI: seated ABI, seatedadjusted ABI using a formula to account for hydrostatic ankle pressure, and traditional supine ABI using a foldable massage table that is 5% of the cost of a medical stretcher. Comparative analysis was performed using the Student t test analysis and one-way analysis of variance. The frequency of completed seated ABI, seated-adjusted ABI, and supine ABI examinations performed at independent MMCs was quantified to determine feasibility. Results: In 166 individuals experiencing homelessness or housing instability who were screened over the course of five MMCs, 89 underwent PAD screening with ABI. Of the patients screened, 38 patients had seated, seated-adjusted, and supine ABIs measured (43% of total number of patients undergoing any ABI measurement). PAD (ABI < 0.9) was identified in one patient using all three ABI methods. Noncompressible ABI (ABI $ 1.3) were identified in 32 patients (32/ 38 [84%]) screened with seated ABI. Of these 32 patients, 24 (75%) continued to have noncompressible ABIs using seatedadjusted ABI. Of these 24 patients, 4 (17%) continued to have noncompressible ABI using supine ABI. The average seated ABI significantly differed from supine ABI (1.34 vs 1.14; P < .0001). The average seated ABI also significantly differed from seated-adjusted ABI (1.34 vs 1.29; P ¼ .026). The average seated-adjusted ABI significantly differed from supine ABI (1.29 vs 1.14; P ¼ .0204). Conclusions: We found that seated and seated-adjusted ABI are grossly inaccurate and more often lead to falsely elevated noncompressible ABI (32/38 [84%] and 24/38 [75%], respectively) compared with supine ABI (6/38 [16%]). We recommend using supine ABI on patients for PAD screening. Supine measurement is technically feasible in outreach mobile clinics using a transportable folding massage table and is a more accurate tool for PAD screening. (JVS-Vascular Insights 2024;2:100125.) Keywords: Ankle-brachial index; Peripheral arterial disease screening; Outreach clinic; Mobile clinics; Homelessness From the Division of Vascular Surgery, Department of Surgery, University of Massachusetts Memorial Medical Centera; the University of Massachusetts Chan Medical Schoolb; and the Diabetes Center of Excellence, University of Massachusetts Chan Medical School.c Supported through the SVS Foundation Vascular Care for the Underserved Pilot Project grant. Correspondence: Tammy T. Nguyen, MD, PhD, Division of Vascular Surgery, Department of Surgery, University of Massachusetts School of Medicine, 55 N Lake Ave, S3-731, Worcester, MA 01655 (e-mail: tammy.nguyen@ umassmemorial.org). The editors and reviewers of this article have no relevant financial relationships to disclose per the Journal policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest. 2949-9127 Ó 2024 The Author(s). Published by Elsevier Inc. on behalf of the Society for Vascular Surgery. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). https://doi.org/10.1016/j.jvsvi.2024.100125 Peripheral arterial disease (PAD) is a rapidly growing health concern affecting >200 million people worldwide and >8.5 million people in the United States.1,2 Poor PAD outcomes have been strongly linked to low socioeconomic status, rurality, and non-White race or ethnicity. Patients who experience limited access to health care are at higher risk of developing severe forms of PAD leading to major lower extremity amputation3e6 and have poorer outcomes after amputation.5 However, ensuring health care access for early PAD diagnosis and prevention in communities with low socioeconomic status, rurality, and non-White race or ethnicity remains a challenge. Mobile health clinics have emerged as a powerful tool to reach patients most impacted by housing insecurities. 1 2 JVS-Vascular Insights Balaparya et al 2024 The use of mobile health clinics can be a cost-effective investment of health care funds7,8 and has been successful in screening patients for PAD among at-risk communities.9,10 Individuals experiencing homelessness and housing instability have been estimated to have a three times greater risk of cardiovascular disease vs housed individuals11 with increasing risk associated with the duration of homelessness.12 In 2020 we implemented a medical-provider-driven mobile multidisciplinary clinic (MMC) focused on PAD and diabetic foot care in patients experiencing housing insecurity.13 Optimal management of vascular disease and diabetic care requires a multidisciplinary approach involving nursing, podiatry, vascular surgery, and social work.14,15 Our MMCs provided a sustainable methodology for leveraging hospital-based resources to build mobile outreach clinics in partnership with local community programs to provide multidisciplinary care to communities impacted by housing insecurities. The ankle-brachial index (ABI) is a widely used PAD screening tool because it is a simple, low-cost, and noninvasive test with an estimated sensitivity of 61% and a specificity of 92% for detecting arterial insufficiency.16 The test uses a blood pressure cuff and Doppler ultrasound imaging to compare the ratio of blood pressure at the ankle with the blood pressure in the arm at the level of the brachial artery as a measure of perfusion to the lower extremities2,17 (Fig 1).2 A low ABI (<0.9) is associated with decreased perfusion to the lower extremities.17,19 In contrast, a high ABI ($1.3) reflects noncompressible arteries, which may be due to vessel calcification, a feature that is found commonly in patients with diabetes (Table I).20 This finding can lead to falsely elevated ABI measurements in patients with diabetes.17,21 Despite this limitation, ABI is a valuable tool in diagnosing PAD. Incorporating the ABI examination ARTICLE HIGHLIGHTS d d d Type of Research: Prospective nonrandomized study Key Findings: Seated and seated-adjusted anklebrachial index (ABI) is inferior to supine ABI for peripheral arterial disease screening in a mobile outreach clinic setting. Take Home Message: Supine ABI is a feasible method to screen for peripheral arterial disease and is more accurate than seated and seatedadjusted ABI measurements. into a mobile clinic presents several technical challenges. Outdoor mobile clinic events may be loud, making it difficult to hear faint Doppler signals. Furthermore, supine ABI testing requires a patient to be flat on a stretcher or examination table, which may be costly and logistically difficult to transport in a nonpermanent, resource-limited community outreach clinic. Therefore, the option to perform a seated ABI measurement to screen for PAD is appealing in a mobile outreach clinic because this method does not require a stretcher or the patient to be supine. To account for the gravitational pressure in seated ABI, a mathematical adjustment using a conversion factor that considers the hydrostatic pressure difference between the arm and ankle in a seated patient has been reported to provide accurate ABI measurements in a vascular laboratory setting.18 We hypothesize that using seated ABI adjustment calculations will provide a feasible and accurate PAD screening method at mobile outreach clinics. In this study, we compared the usefulness of seated-adjusted ABI and supine ABI examinations in mobile outreach clinics. We also examined the feasibility of screening Fig 1. Ankle-brachial index (ABI) measurement methods. The ABI is measured with blood pressure cuff and doppler on arm and ankle with patient in the seated (A and B) or supine position (C). Seated-adjusted ABI measurements (B) were calculated using corrected ABI formula.18 Created with Biorender. SBP, systolic blood pressure. JVS-Vascular Insights Balaparya et al 3 Volume 2, Number C the unhoused population for PAD using seated-adjusted and supine ABI in a mobile vascular laboratory. Table I. Ankle-brachial index (ABI) interpretation: ABI measurement range with corresponding peripheral arterial disease (PAD) diagnosis20 METHODS ABI measurement Data collection. Our study did not require institutional review board approved protocol because no research intervention was performed. Most of our participants were native English speakers. We had native Spanishspeaking volunteers at each event, and we encountered one Mandarin speaking-only participant who required a volunteer Mandarin interpreter. Patient information was collected using a paper medical intake form. Prospective data from patients experiencing housing and financial instabilities were collected at five independent MMCs from 2020 to 2022. MMCs were conducted in partnership with local organizations that have established services to the unhoused and housing insecure communities. PAD screening and other health care services were provided to all patients encountered at MMCs as previously described by Boelitz et al.13 <0.50 Severe PAD 0.79-0.50 Moderate PAD ABI measurement. PAD screening with ABI was performed by certified vascular laboratory technologists using appropriately sized blood pressure cuffs and a portable continuous-wave 8-MHz Doppler transducer (Fig 1). The ABI was calculated by dividing the highest ankle systolic blood pressure at which Doppler signal returned after blood pressure cuff compression by the highest brachial systolic blood pressure at which Doppler signal returned after blood pressure cuff compression of a resting patient.22 Seated brachial and ankle systolic blood pressure measurements were performed with the patient seated in a standard folding chair with the arm rested on a table at the level of the chest. Seated-adjusted ABI was performed in a similar manner as outlined for seated ABI with the addition of measuring the distance between the brachial artery and posterior tibial artery with the patient in the seated position (Fig 1). A correction factor accounting for the distance between the brachial artery and posterior tibial artery with the patient in the seated position and the specific gravity of blood and mercury (0.78).18 The formula is as follows: Corrected ABI ¼ Measured ankle pressure  D  0:078 Measured brachial pressure Supine ABI brachial and ankle systolic blood pressure measurements were performed with the patient lying on a standard massage folding table with a maximum weight capacity of 450 lbs. Patients found to have noncompressible ABIs from all three ABI methods were referred to our institution’s vascular laboratory for toebrachial index (TBI) testing, consistent with our institution’s practice for noncompressible ABI. ABI feasibility assessment. The feasibility of incorporating seated, seated-adjusted, and supine ABI at MMCs Interpretation 0.89-0.80 Mild PAD 0.90-1.29 Normal $1.30 Indeterminant (noncompressible) was determined by comparing equipment cost and the number of patients screened with each ABI measurement method. Statistical analysis. ABI measurements were considered either normal (ABI <1.3 and $ 0.9), mild to moderate PAD (ABI <0.9 and $ 0.5), severe PAD (ABI <0.5), or noncompressible (ABI $ 1.3) (Table I). Statistical differences between seated, seated-adjusted, and supine ABI were performed with two-way analysis of variance and/or Student t test. Statistical significance was determined at the P # .05 level. Analyses were conducted in SPSS 29 (SPSS Inc, Chicago, IL) and Prism 10.2.3 (GraphPad Software, Boston, MA). RESULTS Study cohort. Five MMCs focused on patients experiencing homelessness or housing insecurities were conducted in Central Massachusetts from 2020 and 2022. MMCs were attended by a total of 166 patients; 89 (36%) were evaluated for PAD with ABI testing. An average of 33 patients were evaluated at each MMC over a 4-hour period. Participating patients were primarily men, with an average age of 56 years. ABI measurement methodology. All patients were offered ABI screening; however, the range of ABI testing completed at each MMC varied greatly, between 21% and 97% among MMC events 1 to 5 (Table II). Owing to limited resources, seated ABI was only performed at MMCs 1 and 2. At later MMC events, seated, seatedadjusted, and supine ABIs were performed. A total of the 89 patients underwent PAD screening with one or more ABI measurement method at five MMC events (Table II). Seated ABI examinations were performed on 88 patients (99% of total ABIs) (Table II). The seated ABI measurements at all MMC events ranged from 0.67 to 1.86 with an average of 1.34. Not surprisingly, 67% of patients (59/88) were identified with noncompressible ABIs. Two patients were found to screen positive for PAD, with an ABI of 0.67 and 0.80, with the seated ABI. The remaining 27 patients were found to have normal ABIs. 4 JVS-Vascular Insights Balaparya et al 2024 Table II. Number of patient participants with ankle-brachial index (ABI) measurements at multidisciplinary mobile clinic (MMC) events MMC Date Total MMC patients screened Participants measured Female with any method sex Mean age participants, years Seated ABI measured Seated-adjusted ABI measured Supine ABI measured 48.7 6 15.0 11 n/a n/a November 2020 52 11 (21) 23 (44) June 2021 30 29 (97) 10 (33) 54.1 6 11.9 29 n/a n/a November 2021 23 14 (61) 11 (48) 60.6 6 12.1 14 14 13 May 2022 38 19 (49) 6 (16) 67.3 6 13.9 18 16 15 November 2022 23 17 (74) 7 (30) 48.9 6 13.8 17 12 15 166 90 (54) 57 (34) 55.7 6 15.5 88 42 43 Total Values are number (%) or mean 6 standard deviation. Seated-adjusted ABI examinations were performed on 42 patients (47% of total ABIs) (Table II). The seatedadjusted ABI measurements at all MMC events ranged from 0.59 to 1.75, with an average of 1.29. Noncompressible ABIs were identified in 38% of patients (16/42). Three patients were found to screen positive for PAD, with an ABI of 0.59, 0.80, and 0.87, respectively, with the seated ABI. The remaining 16 patients were found to have normal ABIs. Supine ABI examinations were performed on 43 patients (48% of total ABIs) (Table II) and ranged from 0.70 to 1.95 with an average of 1.14. Noncompressible ABIs were identified in 16% of patients (7/43). Three patients were found to screen positive for PAD, with an ABI of 0.70, 0.79, and 0.87, when measured using supine ABI. The majority, 36 patients, were found to have normal ABIs. Comparison between seated ABI, seated-adjusted, and supine ABI. We were surprised to observe the high percentage of noncompressible ABIs measured using seated-adjusted ABIs when compared with supine ABIs (38% vs 16%) (Fig 2). To test the accuracy of seated and seated-adjusted ABIs when compared supine ABIs, 38 patients had all three screenings ABI methods performed (43% of screened patients). The average seated ABI significantly differed from supine ABI (1.34 vs 1.14; P < .0001) (Fig 2). The average seated ABI also significantly differed from seated-adjusted ABI (1.34 vs 1.29; P ¼ .026) (Fig 2). The average seatedadjusted ABI significantly differed from supine ABI (1.28 vs 1.14; P ¼ .0204) (Fig 2). PAD screening at MMC events yielded a high rate of noncompressible ABIs, in particular when measurements were done with seated ABI (59/89 [66%]) (Figs 3 and 4). Two patients were found to have mild to moderate PAD based on seated ABI. Twentyseven patients were found to have normal peripheral artery perfusion based on seated ABI (27/89 [30%]). To determine whether the noncompressible patient population screened at MMCs had true calcific vessel arterial disease or was falsely elevated owing to seated position, we compared ABI measurements in the seated, seatedadjusted, and supine positions for patients attending MMC events 3 through 5. Seated ABI demonstrated noncompressible PAD in 32 patients (32/38 [84%]) screened. Of the 32 noncompressible seated-ABI, Fig 2. Mean ankle-brachial index (ABI) measured using three different methods at each multidisciplinary mobile clinic (MMC) event. Noncompressible ABI denotated at $1.3. JVS-Vascular Insights Balaparya et al 5 Volume 2, Number C false-positive ABI with low positive predictive value for identifying noncompressible vessels using seated and seated-adjusted ABI, which implies that these methods are not accurate for PAD screening. Fig 3. Distribution of seated ankle-brachial index (ABI) at each multidisciplinary mobile clinic (MMC) event. Noncompressible seated ABI denotated at $1.3. seated-adjusted ABI agreed and was persistently noncompressible in 24 patients (24/38 [63%]). Among patients found to have noncompressible ABI with either seated or seated-adjusted ABI, supine ABI confirmed noncompressible PAD in only four patients and an additional two patients who had tested compressible previously (6/38 [16%]). When compared with the gold standard supine ABI, seated ABI is 83% sensitive for identifying noncompressible PAD, 16% specific, with a 14% positive predictive value and an 86% negative predictive value at accurately identifying noncompressible vessels. Seated-adjusted ABI is 67% sensitive for identifying noncompressible PAD, 38% specific, with a 17% positive predictive value, and 86% negative predictive value at correctly identifying noncompressible vessels (Table III). These data suggest that there is a high number of Feasibility of PAD screening at MMCs. At the first two MMC events, only seated ABIs were performed given the limited MMC budget and infrastructure to perform supine ABIs. Blood pressure cuffs, handheld Doppler machines, and ultrasound gel were donated graciously to MMC events through our academic institution. Seated and seated-adjusted ABI measurements required a folding chair, measuring tape, and table, which were often provided by each hosting organization event free of cost or was purchased for $80. The cost of a stretcher was estimated to be $3000 and weighed 75 lbs. Cost, storage size limitations, and heavy weight made it not logistically feasible for our nonprofit MMC group to perform supine ABI using medical stretchers. At MMC events 3 through 5, supine ABI was performed using a foldable massage table. After obtaining grant funding, MMC purchased foldable massage tables for approximately $150 that weighed 33 lbs. and could support patients #450 lbs. The cost of a foldable massage table is 5% of the cost of a medical stretcher, making the option for supine ABI measurements financially feasible. To test the technical feasibility of performing supine ABI measurements using the massage folding table, the number of patients screened for PAD using any ABI method was compared with the number of supine ABI performed at MMC events 3 through 5. A total of 49 patients had any ABI measurements recorded at MMC events 3 through 5. Of the 49 patients with any ABI measurements, 43 received supine ABIs using the massage Fig 4. Number of compressible and noncompressible ankle-brachial index (ABI) results by ABI measurement methods performed on the same patient cohort. Thirty-eight patients underwent seated, seated-adjusted, and supine ABI measurements. Bars represent the number of compressible ABIs (blue) and noncompressible ABIs (maroon) using the indicated ABI measurement method. Compressive ABI <1.3 and noncompressible ABI $1.3. 6 JVS-Vascular Insights Balaparya et al 2024 Table III. Sensitivity, specificity, positive and negative predictive values for seated-adjusted and seated ankle-brachial index (ABI) Result Noncompressible Compressible Total Noncompressible 4 20 24 PPV: 17% Compressible 2 12 14 NPV: 86% Total 6 32 Seated-adjusted ABI Sensitivity: 67% Specificity: 38% Seated ABI Noncompressible 5 27 32 PPV: 16% Compressible 1 5 6 NPV: 83% Total 6 32 Sensitivity: 83% Specificity: 16% NPV, Negative predictive value; PPV, positive predictive value. Reported values are in reference to gold standard supine ABI. Compressible ABI is <1.3 and noncompressible ABI is $1.3. folding table (43/49 [88%]) (Table II). These data demonstrate that performing supine ABI in a mobile outreach setting is technically feasible. DISCUSSION Rising health care costs and socioeconomically disadvantaged communities contribute to significant disparities in PAD screening.3e5 To address this issue, several groups have implemented mobile clinics to provide accessible PAD screening to underserved populations.9,10,13 As mobile PAD screening clinics expand, it is crucial to understand the unique challenges of screening PAD with ABI measurements in outreach settings. Our study explored the feasibility of introducing vascular screening in an MMC and evaluated different methods of ABI measurement within the resource constraints of this setting. We found that seated and seated-adjusted ABI measurements are unreliable and that, to accurately diagnose PAD, ABIs must be obtained in the supine position. Although supine ABI measurements can be performed easily in a clinic setting, this is not the case in a mobile outreach setting. The medical stretcher required for supine ABI cost approximately $3000 and poses logistic challenges regarding stretcher transportation and longterm storage between MMCs. Furthermore, only 54% of patient participants at MMCs (89/166) agreed to proceed with ABI testing when offered owing to the cumbersome need to remove shoes and socks in a public setting. Owing to these challenges, we evaluated seated ABI testing for PAD screening MMC 1 and MMC 2. Performing seated ABI measurements is appealing at MMCs because it provides fast patient screening turnover. This is evident by the 97% (29/30) of participants receiving seated only ABIs at MMC 2 event over a 4hour period in comparison with ABI testing rates observed at later MMC events when seated-adjusted and supine ABIs were incorporated (an average screening rate of 61% [49/84]) (Table II). However, despite the faster patient screening turnover with seated ABI, this method resulted in a significantly higher rate of falsely positive noncompressible ABI measurements. The high number of patients who had noncompressible seated ABI could be due to increased hydrostatic ankle pressure from patients being in a seated position (Fig 4). To address the issue of falsely elevated seated ABI owing to gravitational effects and to avoid the need for a medical stretcher required for supine ABI measurements, seated-adjusted ABI has been reported to provide accurate ABI measurements for PAD screening.18 Gornik et al18 describe a strong correlation between supine ABI and seated-adjusted ABI (using a corrective factor to adjust for gravitational pressures in the seated position) when performed in a clinical vascular lab setting. In our study, we did not observe a correlation between supine and seated-adjusted ABI, but instead observed a high rate of falsely elevated ABIs obtained using the seated-adjusted calculation. There are important differences between our study design and Gornik et al that may explain these differences. Seated and seated-adjusted ABI measurements in our study were done at MMCs conducted primarily outdoors, which may present difficulties to accurately auscultate changes in Doppler in comparison with a quieter vascular laboratory setting. In Gornik et al, seated-adjusted ABIs were calculated after the supine ABIs were obtained, which may shorten the time of gravity effect on seated ABI measurements. In contrast, in our study, seated ABI measurements were collected before placing the patient in the supine position, thus prolonging the effect of gravity. These differences in study design may account for the discordant correlation between supine ABI and seated-adjusted ABI reported in our study. Based on our experience, supine and supine-adjusted JVS-Vascular Insights Balaparya et al 7 Volume 2, Number C ABI measurements in a MMC setting yielded a high rate of falsely elevated noncompressible ABIs, thus making these ABI methods less accurate for PAD screening at mobile outreach clinics when compared with supine ABI. Based on the superiority of supine ABI for PAD screening at MMCs identified in our study, we have now transitioned to only performing supine ABIs at all MMC events. The technical and logistical challenges of performing supine ABIs at MMCs have been addressed with the use of economical, foldable massage tables with a weight capacity of #450 lbs. The cost of a foldable massage table is 5% of the cost of a medical stretcher, making the option for supine ABI measurements logistically feasible. Finally, it is important to note that establishing ABI testing and encouraging patient participation at MMC required a learning curve as evident by only 21% of total patient participants being screened at MMC 1(11/52) and later an increase of 97% (29/30) ABI testing done at MMC event 2. Patient participation in ABI measurements were encouraged by offering foot washes and podiatry foot examinations immediately before or after ABI testing to limit the number of times patients were asked to remove their socks and shoes. In addition, patient participants who completed ABI testing were incentivized with donated new sneakers and socks. Designing innovative ways in which to promote ABI measurement participation is key to the success of any program intending to screen for PAD. our city. Although clinics were promoted by organizations already connected with the unhoused population and promoted the events weeks in advance, we are aware that individuals who attended were able to transport themselves to the event on foot, were connected directly or indirectly with the organizations advertising the MMCs, and trusted the medical providers enough to participate; this combination of factors could have excluded individuals with limited mobility, without access to local resources, and those who have a mistrust of the health care system. Given these limitations, we have not used these data as representative of the burden of vascular disease among the unhoused population in Worcester, Massachusetts; our focus is on feasibility of screening and identifying the best screening method in the MMC setting. CONCLUSIONS Our findings underscore the feasibility of using ABI screening in mobile clinic settings and the importance of using supine position measurements vs alternative positions. Vascular health for individuals experiencing homelessness and housing insecurity may be improved through mobile clinics but requires addressing environmental challenges and optimizing protocols to ensure accurate diagnosis and equitable health care delivery. Future research should focus on strategies to enhance ABI testing effectiveness in resource-limited environments and improve PAD screening in vulnerable communities. LIMITATIONS AUTHOR CONTRIBUTIONS The MMC environment is inherently variable and unpredictable regarding weather and temperature. Even with an experienced technologist and suitable portable equipment, the variable temperature and noise or patient distractions in a mobile clinic are different from a controlled vascular laboratory. We can compare the results of different ABI measurement methods performed at each MMC to each other but cannot presume that supine ABI measured at an MMC is equivalent to supine ABI measured in a vascular laboratory. In our institution’s vascular laboratory, it is also standard practice to conduct TBI on patients with diabetes and with noncompressible ankle measurements. Unfortunately, this equipment was not feasible to use in the MMC setting owing to cost and ambient temperature requirements for TBI measurements. MMC events are often held outdoors and, therefore, ambient temperature is less controlled than in a vascular laboratory. Changes in ambient temperature can impact vasoconstriction and/ or vasodilation that will impact the accuracy of TBI measurements. We also acknowledge that participants in MMCs may not be representative of the unhoused population in DISCLOSURES Conception and design: SB, TN Analysis and interpretation: SB, RC, JS, DJ, AS, TN Data collection: SB, JL, TN Writing the article: SB, RC, TN Critical revision of the article: SB, RC, JL, JS, DJ, AS, TN Final approval of the article: SB, RC, JL, JS, DJ, AS, TN Statistical analysis: SB, RC, TN Obtained funding: TN Overall responsibility: TN SB and RG contributed equally to this article and share co-first authorship. None. REFERENCES 1. Hess CN, Hicks CW, Kwan TW, McDermott MM. Lower extremity peripheral artery disease: contemporary epidemiology, management gaps, and future directions: a scientific statement from the American Heart Association. Circulation. 2021;144:e171ee191. 2. Nordanstig J, Behrendt CA, Bradbury AW, et al. Peripheral arterial disease (PAD) - a challenging manifestation of atherosclerosis. Prev Med. 2023;171:107489. 3. 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Aboyans V, Criqui MH, Abraham P, et al. Measurement and interpretation of the ankle-brachial index: a scientific statement from the American Heart association. Circulation. 2012;126:2890e2909. Submitted Jun 5, 2024; accepted Jul 21, 2024.