Difference Between Precipitation and Agglutination Reactions

The key difference between precipitation and agglutination reactions is that the antigens are soluble in case of precipitation while they are insoluble in agglutination.

Treatment of infectious diseases is dependent upon their correct diagnosis. Antigen-antibody reactions are techniques in which we measure antigens and antibodies. Among these antigen-antibody reactions, serological reactions are in vitro reactions that are the most popular methods for diagnosis of diseases and for identification of antigens and antibodies. Precipitation reactions and agglutination reactions are some of the common examples of these serological reactions. There is some differences between precipitation and agglutination reactions, which we will explain in this article.

CONTENTS

1. Overview and Key Difference
2. What are Precipitation Reactions
3. What are Agglutination Reactions
4. Side by Side Comparison – Precipitation vs Agglutination Reactions in Tabular Form
5. Summary

What are Precipitation Reactions?

Precipitation reactions are serological assays for the detection of immunoglobulin levels from the serum of a patient with infection. These reactions take place based on the interactions between antigens and antibodies. These interactions result in a precipitate that forms due to the combination of two soluble components; here, antigens and antibodies.

When the antigen and antibody present in optimal proportions, the precipitation reaction occurs via formation of lattices or cross-links. Moreover, in these reactions, the antigens are soluble molecules with a large size. With comparison to the sensitivity of these reactions, Agglutination reaction is more sensitive than precipitation reaction because a lot of soluble antigens and antibody molecules are required to form a visible precipitation reaction. However, it is possible to make a precipitation reaction sensitive by converting it into the agglutination reaction. But, this can be achieved by attaching soluble antigens to large, inert carriers such as erythrocytes or latex beads.

What are Agglutination Reactions?

Mixing of antibodies with their matching antigens on a surface such as animal cell, erythrocytes, or bacteria results in antibodies cross-linking the particles forming visible clumps. This reaction is termed as agglutination. This serological reaction is very similar to precipitation reaction though both are highly specific depending upon specific antibody and antigen pair. Therefore, agglutination reactions are the reaction between antibody and antigen that result in visible clumping. These antibodies are what we call as “agglutinins”. More importantly, an excess of antibody inhibits the agglutination reaction.

Thus, we call this inhibition as “prozone phenomenon”. This reaction is more sensitive, and it occurs optimally when antigens and antibodies react in equivalent proportions.

Furthermore, in clinical medicine, agglutination reactions have many applications. They can be used to type blood cells for transfusion, for identification of bacterial cultures and to detect the presence of a specific antibody in the serum of the patient. Agglutination is primary used to check if a patient has a bacterial infection or not.

What is the Difference Between Precipitation and Agglutination Reactions?

Precipitation reactions are serological assays for the detection of immunoglobulin levels from the serum of a patient with infection. On the other hand, agglutination is the mixing of antibodies with their matching antigens on a surface such as animal cell, erythrocytes, or bacteria, which results in antibodies cross-linking the particles forming visible clumps. This is the fundamental difference between precipitation and agglutination.

Another difference between precipitation and agglutination is that the agglutination reaction is more sensitive than precipitation reaction. Because, a lot of soluble antigens and antibody molecules are required to form a visible precipitation reaction. However, the main difference between precipitation and agglutination, the two serological reactions, pertains to the solubility of antigens. In the case of precipitation, antigens are soluble molecules while in the case of agglutination; antigens are large, insoluble molecules.

Summary – Precipitation vs Agglutination Reactions

Antigens and antibodies are the major reactants of precipitation and agglutination reactions in immunoassays. The difference between precipitation and agglutination reactions is that antigens are soluble in case of precipitation while they are insoluble in agglutination.

Reference:

1. Boundless. “Boundless Microbiology.” Lumen, Lumen Learning. Available here  
2. “Antigen-Antibody Reactions: Agglutination and Types -.” Home -, 12 Nov. 2017. Available here 

Image Courtesy:

1.”Thermal precipitation immunoassay”By Guillaume Paumier (user:guillom) – Own work, (CC BY-SA 3.0) via Commons Wikimedia  
2.”13546513214582″ by CDC/ Dr. F.T. Forrester (Public Domain) via Public Domain Files