Cold agglutinins
Antibodies that make red blood cells clump together when the blood is cold. A low level can be normal, but a high titre can cause 'cold agglutinin disease' — a haemolytic anaemia triggered by cold, sometimes after an infection or linked to a blood disorder.
What it measures
Cold agglutinins are antibodies (usually of the IgM type) that bind to the surface of red blood cells and make them clump together (agglutinate) at cold temperatures, typically in the cooler parts of the body such as the fingers, toes, nose and ears. The test measures the titre — the level of these antibodies — and how they behave at different temperatures. Low levels can be found in healthy people and are not harmful. A high titre, however, can cause disease in two ways: the clumping itself can block small vessels in the cold (causing bluish, painful fingers and toes on cold exposure), and, more importantly, the antibody can trigger the immune system to destroy the affected red cells, producing a cold-triggered haemolytic anaemia. This is called cold agglutinin disease. It can appear after certain infections (classically Mycoplasma pneumonia or infectious mononucleosis), when it is usually temporary, or it can be chronic and associated with an underlying blood disorder such as a lymphoma. The test is requested when a haemolytic anaemia is suspected, particularly if it is worse in cold weather or if the automated blood count shows odd clumping. It is often paired with the direct antiglobulin (Coombs) test.
What a high value can mean
- Cold agglutinin disease — a high titre causing a cold-triggered haemolytic anaemia.
- After certain infections — classically Mycoplasma pneumonia or infectious mononucleosis; usually temporary.
- An underlying blood disorder — chronic cases can be linked to a lymphoma or related condition.
- Cold-triggered symptoms — bluish, painful fingers, toes, nose and ears on cold exposure.
What a low value can mean
- Low / negative (normal) — the expected result; low levels can occur harmlessly in healthy people.
When to discuss with a doctor
The cold agglutinin titre is a targeted test, requested mainly when a haemolytic anaemia is suspected — especially one that seems worse in cold weather, or when the automated blood count is disrupted by red-cell clumping. A high titre supports cold agglutinin disease, which is interpreted alongside the haemoglobin, the markers of red-cell breakdown (a low haptoglobin, high LDH, high reticulocytes and often high bilirubin) and the direct antiglobulin test. Because it can follow an infection (often settling on its own) or reflect an underlying blood disorder, the work-up and any treatment — which includes the simple but important step of keeping warm — belong with a doctor and often a haematologist. Mediora.AI can surface a cold agglutinin result alongside the haemolysis markers so the pattern is visible; the diagnosis and management belong with your specialist team.