Does an abnormal Allen test result preclude radiocephalic (arteriovenous fistula) creation?

Does an Abnormal Allen Test Preclude Radiocephalic Fistula Creation?

An abnormal Allen test does not preclude radiocephalic arteriovenous fistula creation, particularly when using a side-to-end anastomotic technique. The Allen test assesses palmar arch patency, but evidence demonstrates that radiocephalic fistulas can be safely created regardless of the test result.

Evidence Against Using Allen Test as an Absolute Contraindication

The most direct evidence comes from a Nigerian study where side-to-end radiocephalic fistulas were successfully created in 34 patients, including 12 patients (35.3%) with negative (abnormal) Allen tests, without any adverse effects 1. This demonstrates that preoperative Modified Allen's test is not necessary for side-to-end radiocephalic arteriovenous fistulae 1.

What Actually Matters: Vessel Characteristics

The 2006 American Journal of Kidney Diseases guidelines emphasize that preoperative vascular mapping should focus on arterial and venous adequacy rather than collateral circulation testing 2. The critical predictors of radiocephalic fistula success are:

Arterial Requirements

• Radial artery diameter ≥2.0 mm is required for successful fistula creation 2
• Some evidence suggests a minimum diameter of 1.6 mm, though diameters below this are associated with high failure rates 2
• Absence of severe arterial calcification or atherosclerosis 3

Venous Requirements

• Cephalic vein diameter ≥2.5 mm assessed by duplex ultrasound 2
• Veins <2.0 mm diameter have only 16% primary patency at 3 months compared to 76% for veins >2.0 mm 2
• Continuity with proximal central veins without obstruction 2

Clinical Approach Algorithm

Step 1: Perform duplex ultrasound vascular mapping (not Allen test) to assess:

• Radial artery diameter and presence of calcification 2
• Cephalic vein diameter and continuity 2
• Pulse examination and differential blood pressure measurement 2

Step 2: Proceed with radiocephalic fistula if:

• Radial artery ≥2.0 mm diameter 2
• Cephalic vein ≥2.5 mm diameter 2
• No severe arterial atherosclerosis 3

Step 3: Consider alternative access if vessels inadequate:

• Brachiocephalic fistula as second choice 2
• Transposed basilic vein fistula as third option 2

Important Caveats

The anastomotic technique matters: The evidence supporting fistula creation despite abnormal Allen test specifically used side-to-end anastomosis 1. This technique preserves distal radial artery flow, theoretically reducing hand ischemia risk even with poor collateral circulation.

Physical examination findings trump Allen test: A thickened, non-compressible, calcified radial artery on palpation is a more significant predictor of failure than Allen test results 3. Severe atherosclerosis with tram-track calcification should prompt consideration of more proximal access 3.

Radiocephalic fistulas remain first choice when vessel criteria are met, as they preserve proximal vessels for future access, have low steal incidence, and lower infection rates compared to more proximal fistulas 2.

The guidelines emphasize that "a functional fistula is the goal, not the insertion of a fistula with a poor chance at maturing" 2. Therefore, focus preoperative assessment on vessel diameter and quality via duplex ultrasound rather than Allen test results 2.