Abstract: Apparatus and methods for simultaneously obtaining clinical laboratory and arterial blood gas samples are disclosed. The apparatus includes a flow-through plunger configured for being detachably secured to the tip of a standard arterial blood gas syringe. The flow-through plunger has a conduit through the center thereof which permits blood to flow through the plunger into the arterial blood gas syringe. The flow-through plunger preferably has a diameter larger than the diameter of the arterial blood gas syringe. In this way, the combination of flow-through plunger and arterial blood gas syringe function as a plunger assembly for a larger syringe, preferably a clinical laboratory blood sample syringe.Both a clinical laboratory blood sample and an arterial blood gas sample may be obtained by introducing arterial blood into the clinical laboratory syringe barrel and passing the blood through the flow-through plunger into the arterial blood gas syringe.