In a first aspect, there is a device for detecting a substance within blood, including a collecting tube dimensioned to draw in blood through capillary action; a reagent chamber containing a reactive element; and a connector tube providing fluid communication between the reagent chamber and the collecting tube; wherein the connector tubes are dimensioned to draw in blood through capillary action to the reagent chamber. In other aspects, the device can include an outer casing and/or a plurality of reagent chambers each with a reactive element therein.