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Agglutination of red blood cells is called hemagglutination . One common assay that uses hemagglutination is the direct Coombs’ test , also called the direct antihuman globulin test (DAT) , which generally looks for nonagglutinating antibodies. The test can also detect complement attached to red blood cells.

The Coombs’ test is often employed when a newborn has jaundice , yellowing of the skin caused by high blood concentrations of bilirubin, a product of the breakdown of hemoglobin in the blood. The Coombs’ test is used to determine whether the child’s red blood cells have been bound by the mother’s antibodies. These antibodies would activate complement, leading to red blood cell lysis and the subsequent jaundice. Other conditions that can cause positive direct Coombs’ tests include hemolytic transfusion reactions , autoimmune hemolytic anemia , infectious mononucleosis (caused by Epstein-Barr virus ), syphilis , and Mycoplasma pneumonia . A positive direct Coombs’ test may also be seen in some cancers and as an allergic reaction to some drugs (e.g., penicillin).

The antibodies bound to red blood cells in these conditions are most often IgG , and because of the orientation of the antigen-binding sites on IgG and the comparatively large size of a red blood cell, it is unlikely that any visible agglutination will occur. However, the presence of IgG bound to red blood cells can be detected by adding Coombs’ reagent , an antiserum containing antihuman IgG antibodies (that may be combined with anti-complement) ( [link] ). The Coombs’ reagent links the IgG attached to neighboring red blood cells and thus promotes agglutination.

There is also an indirect Coombs’ test known as the indirect antiglobulin test (IAT) . This screens an individual for antibodies against red blood cell antigens (other than the A and B antigens) that are unbound in a patient’s serum ( [link] ). IAT can be used to screen pregnant women for antibodies that may cause hemolytic disease of the newborn . It can also be used prior to giving blood transfusions. More detail on how the IAT is performed is discussed below.

A) Diagram of direct Coomb’s test. 1.  Blood sample from a patient with hemolytic anemia with antibodies attached to red blood cells. 2. Antibodies coat the patient’s red blood cells. 3. A few drops of Coomb’s reagent (containing anti-human antibodies) is mixed in with the patient’s blood sample. 4. Agglutination reaction (clumping) is visible after cross-linkage of antibodies. B) Diagram of indirect Coomb’s test. 1. Patient's serum containing antibodies is drawn. 2. Donor blood is added. 3. Patient's antibodies bind to donor's red blood cells. 4. A few drops of Coombs’ reagent are mixed with the sample. 5. Agglutination reaction is observed.
The steps in direct and indirect Coombs’ tests are shown in the illustration.

Antibodies that bind to red blood cells are not the only cause of hemagglutination. Some viruses also bind to red blood cells, and this binding can cause agglutination when the viruses cross-link the red blood cells. For example, influenza viruses have two different types of viral spikes called neuraminidase (N) and hemagglutinin (H), the latter named for its ability to agglutinate red blood cells (see Viruses ). Thus, we can use red blood cells to detect the presence of influenza virus by direct hemagglutination assays (HA), in which the virus causes visible agglutination of red blood cells. The mumps and rubella viruses can also be detected using HA.

Questions & Answers

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kasia Reply
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Gift Reply
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Chetan Reply
What are the five types of serological tests used to identify microorganism in the laboratory?
Prudence Reply
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Nankya Reply
It's technique to differentiate bacterial species.The method is discovered by Hans Christian Gram. The bacteria is differentiated as gram positive and gram negative on the basis of peptidoglycan layer which is present in cell wall. The gram positive have peptidoglycan layer.
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Antonie van Leeuwenhoek.
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Timaka Reply
chicken pox
Patients with disseminated herpes zostermay present with severe abdominal pain that results from visceral involvement of varicella-zoster-virus infection. In immunocompetent individuals herpes zoster usually is a localised illness, affecting the skin of one or two adjacent dermatomes.
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Estar Reply
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poor hygiene of the area and unprotected sex with infected partner
poor hygiene,some times having sex with infected person or when normal flora enters in the vagina
unprotected sex and poor hygiene are the major but keep in mind that there are some other minor causes also
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Sumaiyah Reply
So many factors might be the cause viz. Defects of blood capillaries and certain organs like the liver, the kidneys e.t.c
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there may be fevers which cause septicemia
even taking drug, and eating junk foods .
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anaparthi Reply
Structure of bacteria
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Outline the classification of viruses according to morphology, nucleic acid, type of diseases, antigenic reaction
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Mukomya Reply
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Father of microbiology is Anton von Leuuwenhoek
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nowhere because our body alone also contain billions of microbes.
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Bangladeshi people's body contain thrice the amount of microbes than regular people.
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Cocci are bacterias
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Vibrio cholarea
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Antoni van Leeuwenhoek, the father of micro biology

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