thnx kavish..but wat bout left medial rotation,i 131,
mc substance abuse..shape of cervix..this 6 hr wait from now on..is killin me..havin bugs in my stomach..i ges results expected today around 4?
Q.I used in scanning I 123
p.1586,1587 goodman gilman 10thed.
but if the q asks radioimmunoassay then ans is I 125
REF:dutta 67
now i am confused what was asked,i felt that was scanning & i marked I 123,
& i think ans. should be tobacC,but no confirmed ref as yet
Radioimmunoassay
The technique of radioimmunoassay has revolutionized research and clinical practice in many areas, e.g.,
blood banking
diagnosis of allergies
endocrinology
The technique was introduced in 1960 by Berson and Yalow as an assay for the concentration of insulin in plasma. It represented the first time that hormone levels in the blood could be detected by an in vitro assay.
The Technique
A mixture is prepared of
radioactive antigen
Because of the ease with which iodine atoms can be introduced into tyrosine residues in a protein, the radioactive isotopes 125I or 131I are often used.antibodies against that antigen.
Known amounts of unlabeled ("cold") antigen are added to samples of the mixture. These compete for the binding sites of the antibodies.
At increasing concentrations of unlabeled antigen, an increasing amount of radioactive antigen is displaced from the antibody molecules.
The antibody-bound antigen is separated from the free antigen in the supernatant fluid, and
the radioactivity of each is measured.
From these data, a standard binding curve, like this one shown in red, can be drawn.
The samples to be assayed (the unknowns) are run in parallel.
After determining the ratio of bound to free antigen in each unknown, the antigen concentrations can be read directly from the standard curve (as shown above).
Separating Bound from Free Antigen
There are several ways of doing this.
Precipitate the antigen-antibody complexes by adding a "second" antibody directed against the first. For example, if a rabbit IgG is used to bind the antigen, the complex can be precipitated by adding an antirabbit-IgG antiserum (e.g., raised by immunizing a goat with rabbit IgG). This is the method shown in the diagram above.
The antigen-specific antibodies can be coupled to the inner walls of a test tube [View another example]. After incubation,
the contents ("free") are removed;
the tube is washed ("bound"), and
the radioactive of both is measured.
The antigen-specific antibodies can be coupled to particles, like Sephadex. Centrifugation of the reaction mixture separates
the bound counts (in the pellet) from
the free counts in the supernatant fluid.
Radioimmunoassay is widely-used because of its great sensitivity. Using antibodies of high affinity (K0 = 108–1011 M−1), it is possible to detect a few picograms (10−12 g) of antigen in the tube. [Link to page that discusses antibody affinity]
The greater the specificity of the antiserum, the greater the specificity of the assay. Link to an illustration of antibody specificity demonstrated by radioimmunoassay.
The main drawbacks to radioimmunoassay are the expense and hazards if preparing and handling the radioactive antigen.
Both 125I or 131I emit gamma radiation that requires special counting equipment;
The body concentrates iodine atoms — radioactive or not — in the thyroid gland where they are incorporated in thyroxine (T4).
The enzyme-linked immunosorbent assay (ELISA) has many of the advantages (e.g., sensitivity, ease of handling multiple samples) without the disadvantages of dealing with radioactivity. Link to a description of ELISA
Despite these drawbacks, RIA has become a major tool in the clinical laboratory where it is used to assay
plasma levels of:
most of our hormones;
digitoxin or digoxin in patients receiving these drugs;
certain abused drugs
for the presence of hepatitis B surface antigen (HBsAg) in donated blood;
anti-DNA antibodies in systemic lupus erythematosus (SLE).
What are iodine radioisotopes used for?
Iodines are among the most widely used radionuclides, mostly in the medical field. Because of its short half-life and useful beta emission, iodine-131 is used extensively in nuclear medicine.
Its tendency to collect in the thyroid gland makes iodine especially useful for diagnosing and treating thyroid problems. Iodine-123 is widely used in medical imaging, and I-124 is useful in immunotherapy.
Iodine's chemical properties make it easy to attach to molecules for imaging studies. It is useful in tracking the metabolism of drugs or compounds, or for viewing structural defects in various organs, such as the heart.
A less common isotope, iodine-125, is sometimes used to treat cancerous tissue.
Iodine-129 has little practical use, but may be used to check some radioactivity counters in diagnostic testing laboratories.
q.When an untrained person acsends , max benefit is obtained by
a.decrese work load and increase duration of excercise
b.increase workload and decrease duration of excercise
c.increase workload and inhaling oxygen
d. decrease workload
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