Deck 6: Agglutination and Precipitation Reactions: the Unlabeled Immunoassays

Question 1

In an Ouchterlony plate, a precipitin line of identity forms between 2 Ags and an Ab, the 2 lines

A) cross
B) merge
C) cross on 1 side only
D) form 2 separate lines

Answer 1

Ouchterlony analysis is a double diffusion method where, the antigen and the antibody diffuse through gel medium. The diffusion of antibody and antigen results in the formation of a cross-linked complex, which is marked by the formation of a precipitin line. The precipitin line formed between antibody and two antigens will not cross. It also will not cross on one side. There will not be a formation of two separate lines.
Hence, the options a, c and d are incorrect.
The two lines formed in an Ouchterlony plate on reaction of 2 antigens and an antibody will merge. This is because the two isotopic antigens will have a single line of precipitation with an antibody.
Hence, the correct answer is option .

Question 2

A prozone effect

A) occurs in agglutination and precipitin reactions when there is antigen excess
B) occurs in agglutination and precipitin reactions when there is antibody excess
C) occurs in agglutination but not in precipitation reactions
D) occurs in enzyme immunoassay and fluorescent immunoassays when there is antigen excess

Answer 2

The prozone effect, also called as the hook effect, is marked by false negative results. It does not occur in enzyme and fluorescent immunoassays, where there is excess antigen present. It occurs in both agglutination and precipitation reaction. It does not occur due to the presence of excess antigens.
Hence, the options a, c and d are incorrect.
The prozone effect occurs in both agglutination and precipitation reactions. It occurs when high antibody concentrations are present. This excess concentration inhibits the agglutination or precipitation reaction between the antigen and antibodies, resulting in false negative results.
Hence, the correct answer is option .

Question 3

Which of the following describes agglutination?

A) soluble Ag + soluble Ab
B) particulate Ag + soluble Ab
C) reaction that requires instrumentation to read
D) reaction that requires covalent binding to the Ab molecule

Answer 3

The clumping of two or more particles is called as agglutination. This technique is generally used for the purpose of determining blood group. This includes agglutination of red cell antigens with antibodies and is called hemagglutination.
It the case of soluble antigen and antibody, agglutination does not occur. It results in the formation of a soluble immune complex. The reaction does not require an instrument to read the results, it can be seen by the naked eyes. There are no covalent interactions involved in agglutination reactions.
Hence, the options a, c and d are incorrect.
The interactions between particulate antigen and antibodies result in formation of visible clumps. This is called as agglutination. It is similar to precipitation reactions, but the antigens in agglutination are easily sedimented and large.
Hence, the correct answer is option .

Question 4

Which of the following enhances agglutination of charged particles?

A) increasing the ionic strength
B) removing albumin from the reaction buffer
C) decreasing viscosity
D) decreasing ionic strength

Question 5

A direct agglutination reaction involves an

A) antigen that is already part of the particle
B) antigen that has been covalently attached to the particle
C) antigen that has been attached with van der Waals forces to the particle
D) antibody that has been covalently attached to the particle

Question 6

Agglutination reactions involve all of the following except

A) van der Waals, hydrophobic and hydrophilic interactions, electrostatic interactions, hydrogen bonding
B) covalent attachment of something to an antibody molecule
C) Ab and Ag reaction
D) zones of equivalence

Question 7

In radial immunodiffusion by the Mancini method, the

A) concentration of the antigen is directly proportional to the ring diameter
B) concentration of the antigen is inversely proportional to the ring diameter
C) concentration of the antigen is directly proportional to the ring diameter squared
D) time required is less than that for the Fahey method

Question 8

A direct antiglobulin test

A) measures the amount of antibody in the RH2 mom that reacts with the RH1 fetal red blood cells
B) determines whether anti-RH is already present on the newborn's red blood cells
C) measures the amount of antibody produced by the fetus to the mother's red blood cells
D) uses cross-linking antibodies of the IgD type

Question 9

When a light shines directly through a solution and the amount of light that goes through the sample (directly across) is measured as the amount of complex formation, this is called

A) nephelometry
B) turbidometry
C) spectrophotometry
D) fluorescence

Question 10

If a patient shows the signs and symptoms of severe rheumatoid arthritis but the 1:40 dilution of her sera did not show an agglutination reaction,

A) we should use an enzyme immunoassay instead, because we need a more sensitive assay
B) we should test for other forms of arthritis
C) we should serially dilute the serum and run the test again
D) we should report to the physician that she is negative for rheumatoid factor

Question 11

A physician came into your laboratory and wants a stat result on the immunoglobulin level in a patient's sera. You have an RID commercial kit for immunoglobulin levels. How soon can you give the physician the results, remembering that the physician wants a stat, or fast, result?

A) 18 hours by the Mancini method
B) 18 hours by the Fahey method
C) 48 hours by the Mancini method
D) 48 hours by the Fahey method

Question 12

If an Ouchterlony were repeated using twice as much total antigen concentration in the well as used originally, the Precipitin line would be

A) closer to the antibody well
B) closer to the antigen well
C) in the same place
D) not enough information is available to decide between the above answers