Final answer:
The test ordered for a patient with a known cold agglutinin is a cold agglutinin test. It requires careful handling to prevent activation of autoantibodies; the blood will be prewarmed to ensure accurate results. The presence of cold agglutinins can be indicative of blood type AB if both anti-A and anti-B antibodies cause agglutination.
Step-by-step explanation:
The test ordered for a patient known to have a cold agglutinin, which requires an EDTA whole blood tube collected in a prewarmed tube and remaining warm until testing, is likely a cold agglutinin test. This type of test detects the presence of cold agglutinins, which are autoantibodies that can cause red blood cells to agglutinate, or clump together, at low temperatures. The prewarming of the tube is essential to prevent the autoantibodies from activating, which otherwise might lead to a misinterpretation of the blood sample. When anti-A and anti-B antibodies are added to the sample and agglutination occurs in both, as described earlier, it indicates that the patient has blood type AB. Such a response is a normal finding and suggests that the patient possesses both A and B antigens on the surface of their red blood cells.