Abstract: A two piece neurodiagnostic test instrument sensitive to the prevalence of blood borne pathogens in a clinical environment. The test instrument provides a weighted balance to conduct a proper neurodiagnostic test without fear of puncturing a patient's skin. The instrument alone and without additional force applied by the physician provides the necessary weight to achieve accuracy and consistency during an examination procedure. The test instrument includes a weighted stainless steel reusable handle with a disposable plastic pinwheel test head releasably attached thereto. The test head includes a first end with coupling arms which are inserted into a receptacle in a first end of the weighted handle. A second end of the test head includes a rotatable pin wheel with a shroud disposed around an upper portion of the pin wheel. The weighted handle includes a hollow elliptical tube with a spring biased ejector bar received inside the tube.