RADIOIMMUNOASSAY (RIA):Principle, Procedure, Application and MCQ for GPAT, NET JRF and GATE exam

RADIOIMMUNOASSAY (RIA):Principle, Procedure, Application and MCQ for GPAT, NET JRF and GATE exam


  • This techinque is used to determine concentration of antigen in given sample.
  • This techinque is very sensitivity it can detected 0.001 μg/ml.
  • This techinque was introduced in 1960 by berson & yalow.


  • It involves three principles which make it most specific & sensitive than other immune assays.
  • An immune reaction i.e. antigen,antibody binding.
  • A competitive binding or competitive displacement reaction
  • Measurement of radio emission (it gives sensitivity)


All immunoassay require the use of labeled material in order to measure the amount of antigen or anti body present.

A label is a molecule that will react as part of the assay so a change in signal can be measured in the blood : reagent solution.


  • A known quantity of an antigen is made radio active frequently by labeling it with gamma radioactive isotopes of iodine attached to tyrosine.
  • This radio labeled antigen is then mixed with a known amount of antibody for that antigen and as a result the two chemically bind to one another.
  • Then a sample of serum from a patient containing an unknown quantity of that same antigen is added.
  • This causes the unlabeled anti gen from the serum to complet with the radio labeled antigen for antibody binding site.
  • The concentration of cold antigen is increased more of it binds to the antibody displacing the radiolabled variant and reducing the ratio of antibody – bound radio labeled antigen to free radio labeled antigen.
  • The radioactivity falls because unlabelled antigen dilute it.
  •  The count obtained from the radioactivity are used to determine the hapten concentration in the sample the interpretetion being done on the standard curve.
  • Test tube-1 blank Ab +Ag
    Test tube-2  calibrator Ab+pure Ag + Ag
    Test tube-3 sample Ab + sample A g + Ag
  • Radioimmunoassay (RIA)


  1. Micro titer plate/ test tube
  2. Pure antigen
  3. Radio labelled antigen
  4. Anti body
  5. Standards
  6. Centrifuge
  7. Radio active counter


  1. Micro titer plate :- A micro titer plate is used mostly used for this assay. A microtiter plate could have 6,24,96,384 or even sometimes 1536 wells arranged in rows.Each well of a microplate can only hold very small amount of liquid.
  2. Pure antigen :- Antigen may be obtained from biological sample or by synthetic form it should be pure. It is used as standard or calibrator.
  3. Radio labelling of antigen :- The most commonly used radiolabels in RIA are tritum and iodine.They have adequate activity and have long enough half lifes.
  4. Antibody :- sepcific antib0dies are obtained by injecting the Ag to animals.
  5. Standards :-
  6. CENTRIFUGE :- Used for the separation of precipitated from and supernatant liquid from. Range : 1200-2500 rpm
  7. Radio active counters :- two types of counters are used.1.gamma counter 2. scintillation counters
  • Gamma counter:- these are used for the gamma energy emitting isotopes
  • Scintillation counter :- These are used for counting beta energy emitting isotopes

• Separation techniques :-

  • After completion of reaction of reaction free from and bound forms are determined by separation techniques.
  • Various technique include gel filtration, electrophoresis, solid phase adsorption of Ag,Ab & fractional precipitate.


  • RIA is used in the assay of drug like amphetamine,barbiturates,digitoxin,morphine etc.
  • In analysis of vitamine like riboflavin,folic acid.
  1. Digitoxin or digoxin in patients receiving these drugs.
  2. Certain abused drug.
  3. It is used to assay the presence of hepatitis B surface anti gen in donated blood.


1. Which technique is used to assay drug concentration in plasma ?

A. IR sepctroscopy

B. UV sepctroscopy

C.Non aqueous titration


2.RIA was developed by

A.  Berson & Yalow

B. chals & wastone

C. vector&logan

D. lewis & bronstand

3.How many microgram antigen detected in sample by RIA ?

A.0.1 μg/ml

B.0.0001 μg/ml

C.0.001 μg/ml

D.0.01 μg/ml

4.Which sentence is not true about RIA?

A.The most commonly used radiolabels in RIA are tritum and iodine.

B.Centrifugation rpm is 1200-2500.

C.This techinque is very sensitivity it can detected 0.001 μg/ml

D.This techinque is very sensitivity it can detected 0.01 μg/ml

5.RIA standarded graph as

A. X-axis = % Radioactivity and Y.-axis = unlabled Ag(ng)

B.X-axis = unlabled Ag(ng) and Y.-axis = % Radioactivity

C.X-axis = % Radioactivity and Y.-axis = unlabled Ag(mg)

D.X-axis = Radioactivity and Y.-axis = unlabled Ag(ng)

6.Which is not application of RIA ?

A.It is used to assay the presence of hepatitis B surface anti gen in donated blood.

B.In analysis of vitamine like riboflavin

C. T4 &  T3 measurement

D.Digitoxin or digoxin in patients receiving these drugs and measurement its concentration.


1. D






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—Textbook of microbiology by Prescott, Harley.

—Practical analytical chemistry by BECKEET.





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