What does agglutinin mean?
An agglutinin is any substance — most commonly an antibody — that causes cells or particles to clump together, a process known as agglutination. The term belongs chiefly to immunology and hematology: when an agglutinin binds to matching antigens on the surfaces of bacteria or red blood cells, it can link them into visible clusters, a reaction that underpins classic blood typing and many diagnostic tests. Clinicians distinguish cold agglutinins, which act best at reduced temperatures, from warm agglutinins, which are active at body temperature; some of these antibodies are implicated in autoimmune conditions such as cold agglutinin disease. Not all agglutinins are antibodies — certain plant proteins called lectins also provoke clumping. Derived from the Latin root for 'to glue together', the word vividly captures its function: an agent that makes cells stick. It remains a staple term in medical laboratories worldwide.
nounAn antibody, or other substance, that causes particles such as bacteria or red blood cells to clump together (agglutinate). Agglutinins are key reagents in immunology, blood typing, and diagnostic tests.
- Immunology: an antibody that causes antigen-bearing cells or particles to agglutinate (clump together).
- More broadly: any non-antibody substance, such as a lectin, that induces clumping of cells.
"The patient's serum contained an agglutinin that caused the bacterial cells to clump visibly in the test tube."
"Blood typing relies on agglutinins in the test serum to reveal which antigens sit on the surface of the red cells."
"Cold agglutinins can cause red blood cells to clump at low temperatures, a phenomenon exploited in certain laboratory diagnoses."
The plural is standard and commonly used when referring to multiple agglutinating antibodies, as in discussions of a patient's antibody profile.
"Both anti-A and anti-B agglutinins were present in the donor's plasma."
The letters A, B, and O in your blood type are named after the agglutinins your plasma carries — mix the wrong ones and your red blood cells literally glue themselves together.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of agglutinin
Agglutinin derives from the Latin verb agglutinare, meaning 'to glue or fasten together', formed from ad- ('to, toward') plus gluten ('glue'). The term was coined in the late nineteenth century within the new science of bacteriology and immunology, as researchers observed that sera could cause bacteria to clump. It shares this Latin root with related terms such as agglutination, agglutinate, and agglutinogen, all central to serological vocabulary.
How agglutinin is actually used
A technical term used almost exclusively in immunology, hematology, microbiology, and related laboratory sciences; it would rarely appear outside scientific or medical writing. In clinical contexts it often appears in compound forms such as 'cold agglutinin' or 'warm agglutinin', referring to antibodies active at lower or higher body temperatures respectively. The plural 'agglutinins' is common when discussing multiple such antibodies.
Easily confused with agglutinin
Agglutination is the clumping process itself, whereas an agglutinin is the substance (usually an antibody) that causes that clumping.
An agglutinogen is the antigen on a cell's surface that an agglutinin binds to; the agglutinin is the antibody doing the binding.