Cutaneous wound Positive probe-to-bone test 2024-08-06T16:34:54Z Abnormal probe-to-bone test An abnormal result of the probe-to-bone (PTB) test. The PTB test is performed by inserting a sterile, metal surgical probe into the ulcer and is positive if a hard, gritty surface is felt inside. For large wounds, this may require gentle exploration of the wound with the probe. The basis behind the PTB test is that if a probe can reach bone, so can bacteria.