What does agglutination refer to?

Agglutination refers to the clumping together of blood corpuscles, primarily red blood cells. This process occurs when antibodies bind to specific antigens on the surface of the blood cells, causing them to stick together or agglutinate. This phenomenon is significant in immunology and blood typing, as it can indicate the presence of specific blood group antigens and help in matching blood types for transfusions.

In contrast, absence of menstruation pertains to amenorrhea, which is unrelated to the clumping of blood cells. Improvement or moderation addresses changes in condition but does not pertain to the specific biological process of agglutination. The presence of serum protein in urine, known as proteinuria, relates to kidney function and is also separate from the concept of agglutination. Thus, the correct answer accurately captures the essential definition of agglutination within a medical context.