A mains electricity (AC-powered) laboratory instrument intended to be used for the qualitative and/or quantitative in vitro examination of platelet function in a clinical specimen, by inducing platelet aggregation through the addition of platelet aggregating agents. The instrument may incorporate various technologies including electrical impedance, photometry, turbidimetry and/or luminescence together with sample processing, data processing and/or data display software. The device operates with minimal technician involvement and complete automation of all procedural steps.