Objective: The modified Allen test (MAT) is an accepted but controversial way to evaluate palmar arch patency. There is a current lack of consensus in the literature regarding the reliability of the MAT. We hypothesized that the MAT is an inaccurate tool in determining the patency of a patient's palmar arch.Methods: We completed a prospective study at a single universityaffiliated institution. All patients presenting to the operating room or to the vascular surgery clinic for an arteriovenous fistula were enrolled beginning in June 2015. For each patient, a surgical resident in the third year of training or higher performed a physical examination including a MAT on both upper extremities. In-clinic palmar arch duplex ultrasound (US) was then performed by Registered Physician in Vascular Interpretation-certified vascular surgeons who were blinded to the results of the MAT. Univariate analysis was performed to evaluate the utility of the MAT.Results: There were 32 patients enrolled and 59 arms evaluated. Five arms were excluded because of indeterminate US findings or patient factors that limited an adequate physical examination. The MAT was positive for an incomplete arch in 14 (24%) arms, whereas US instead identified 23 (39%) incomplete arches. Of all 59 examinations performed, there were 5 (8.4%) false positives and 14 (24%) false negatives resulting in 19 (32%) discordant examinations (P ¼ .03; Table ). The sensitivity of the MAT was 39% (95% confidence interval [CI], 20%-61%), the specificity was 86% (95% CI, 70%-95%), the positive predictive value was 64% (95% CI, 36%-86%), and the negative predictive value was 69% (95% CI, 53%-81%). The accuracy of the MAT was 68% (95% CI, 37%-98%).Conclusions: The MAT is inaccurate and lacks sensitivity and is thus a poor tool for assessing palmar arch patency. We recommend that palmar arch duplex US be used as the primary diagnostic tool for evaluating the collateral circulation of the hand, especially before procedures that may compromise radial artery blood flow.
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