A portable, disposable in-vitro diagnostic apparatus is provided. The apparatus includes a body configured to be hand held. The body has a reaction medium supply chamber configured in selective fluid communication with a reaction chamber via a fluid conveying channel. The reaction chamber is located beneath a sample reaction chamber. The reaction medium supply chamber contains a reaction fluid therein and the reaction chamber contains a thermal reaction medium therein. The reaction fluid is selectively reactive with the thermal reaction medium to produce one of an endothermic or exothermic reaction beneath the sample reaction chamber.