Final answer:
The top of the tube for Monospot testing should be blue-green.
Step-by-step explanation:
The top of the tube for Monospot testing for mononucleosis should be blue-green.
The Monospot test is a qualitative assay for the detection of heterophile antibodies, which are an indicator of infectious mononucleosis. The test uses specially treated horse red blood cells. If heterophile antibodies are present in the patient sample, the red blood cells will agglutinate and appear as dark clumps against a colored background.
In a positive reaction, the dark clumps will be moderate-to-large in size and will appear against a blue-green background, which is the color of the top of the tube.