False Negatives
The Possibility of False Negative Results
When conducting the Allen test, there is a chance of obtaining a false negative if the procedure is not performed correctly by the physician. False negative results can lead doctors to proceed with cannulation, which may restrict blood flow to the hand. This is why a modification involving three digits is often implemented.
Variations in Arterial Locations
In certain individuals, the radial and ulnar arteries may be located slightly differently. Consequently, doctors may fail to adequately block the arteries during the test if the size of the thumb is insufficient. This discrepancy in arterial placement underscores the importance of the three-digit Allen test, as it provides a larger surface area for more accurate results.
Complications
While the Allen test itself is generally safe, there are potential complications that can arise from false negatives. One such complication is ischemia, which occurs when tissues do not receive an adequate amount of blood and, subsequently, oxygen. Without oxygen, the cells in the tissue cannot carry out their metabolic functions, leading to tissue death. Blockages in the radial artery are often associated with ischemia. In situations where a medical procedure is performed with only the ulnar artery supplying blood to the hand, there is a risk of the hand becoming ischemic. Fortunately, most individuals who experience insufficient blood flow from the ulnar artery in one arm will have proper blood flow in the other arm. The Allen test can be used to determine the blood flow status in each arm.