Final answer:
EDTA contamination in a plasma sample can disrupt or prolong the coagulation test by interfering with the role of calcium ions in the blood clotting process.
Step-by-step explanation:
When a plasma sample of a patient is contaminated by the metal ion chelating agent EDTA, it will interfere with the blood coagulation test. EDTA works by chelating or binding to metal ions like calcium. In the coagulation process, calcium ions are necessary for the enzymic conversion of prothrombin into thrombin, which is crucial for blood clotting. However, if EDTA is present in the plasma, it will bind to the calcium ions and prevent them from participating in the coagulation process, leading to a disrupted or prolonged coagulation test.