Testing lead conditions in an implantable medical device includes continuously sampling the impedance values of a lead associated with the implantable medical device. The sampling is conducted over a predetermined period of time. An impedance histogram is then generated using the sampled impedance values by separating each measured impedance value into a specific bin assigned to contain a particular range of impedance levels. The lead condition of the tested lead can then be determined based on one or more characteristics of the impedance histogram.