Method and apparatus for testing dielectric insulation integrity of a device

A method, apparatus 300 and detection circuit 306 for testing the dielectric integrity of an insulated medical instrument 316 such as a diathermy probe, submerged in a conductive solution 320 during test. The circuit supplies a test voltage to the device under test via connector 308, and a representation of the test voltage is compared with a reference or threshold potential to determine whether it is representative of a loading effect, due to a flaw or defect in the insulation integrity significantly lowering resistance and allowing a current to flow to the electrolyte. In embodiments, visual 312, 314 and audible 322 devices alert or notify the operator of a failed or passed test and a wetting agent can be used to ensure maximal surface contact with the insulation coating. In this manner, a uniform test is performed, batch testing is possible and damage caused via sparking is reduced.