Final answer:
The first step in reading hemagglutination reactions is the resuspension of red blood cells (RBCs), which is essential for accurate test results.
Step-by-step explanation:
The first step in reading hemagglutination reactions is resuspension of RBCs. Before grading agglutination or checking the supernatant for hemolysis, it is crucial to ensure that the red blood cells (RBCs) are uniformly suspended in the solution to accurately interpret the results.
This step facilitates the interaction of antigens and antibodies during the assay and supports consistent observations across test samples.