1. RADIO IMMUNOASSAY
DANIEL CASAL

2. What is radioimmunoassay
Sensitive method that measures small amounts of substances in the blood
Able to measure drugs, antigens and hormones
Any biological substance where an antibody exists can be measured
Uses include drug detection, blood bank screening for certain viruses and cancers (such as HIV and Hepatitis B)
Immunoassays produces signals in response to binding
Able to be detected by many ways such as it showing a color change, fluoresces under light, or emitting radiation.

3. Radioimmunoassay relevance
Most common method to test for drugs of abuse
Screens presence of drugs in different areas such as forensic toxicology and clinical toxicology
(Dated back from 1970 when soldiers were coming back from the Korean war)
Take a urine or blood sample since its easy to collect and obtain in large quantity
Radioimmunoassay technique isolated Diphenyldantoin from semen, blood stains saliva and dried saliva stains.

4. Radioimmunoassay Relevance
Testing Opiates for morphine content is mostly performed in forensics urine drug test laboratories
Doses of hydromorphine, hydrocodone, oxymorphone and oxycodone were administered to individuals. Urine sample were collected before and after the drugs were administered.
The radioimmunoassay testing indicated that 3 of the 4 drugs were detectable by urine
(Low to moderate concentrations of these drugs will go undetected when testing)

5. Method
First obtain a substance that contains the antigen (containing antiserum)
Introduce antigen with radioactive chemicals and then incubate it at +4C
(Isotopes used are H3, I 125, I 131, C14 because they emit gamma rays).
Most common is I 125 or I 131 (easier for Iodine atoms to be introduced in tyrosine residue)
Mix the antibodies and the radioactive antigen
Both substances bind with each other and end up forming a new substance
Add unknown substance (Also known as “cold”)
This causes the antigens in the new/unknown substance to bind with the antibodies

6. Method
The unknown substance displace the isotope substance that was originally joined together with the antigen.
If there is in increase in the cold antigen, there will be an increase in the radioactive antigen being displaced from the antibody molecule
Able to measure radioactivity and a standard biding curve is shown
Separate the bound from free antigen by precipitating the antigen antibody

10. Chemistry in radioimmunoassay
Very useful in quantitative analysis of drugs.
Antibodies reacting with specific elements to get a measurement
Detection limit depends if the solution was in a liquid phase, or in a solid phase

11. Safety Always wear goggles, apron, and gloves at all times
Be careful when handling the radioactive isotopes
Stay away from the gamma rays being emitted during the radioimmunoassay process
Dispose of the hazardous material accordingly

12. Problems/difficulties
If your test tube isn’t cleaned then the sample will be contaminated
Plug in wrong data
Properties of specimens difficult to detect
Interference
Malfunction on the instrument used to count the radioactivity
Radioactive isotope
Antibodies and antigens aren’t pure

13. Limitations
Really sensitive (smallest concentration of a substance that can be measured reliably
Specificity depends on the antigen and the antibody and the isotope
Contaminants affect both the precision and the accuracy of quantitative data
Detection limits depend on the standard curves of the sample and it depends of the substance

14. Advantages
Really sensitive and precise
Able to detect small trace amounts
Require small concentration of antigens
Large capacity
Disadvantages
Usage of radioactive chemicals are extremely dangerous
Only special trained individuals are allowed to perform the lab
Require lots of arrangements and time to store/dispose radioactive material
Expensive equipment
Require pure antibodies and antigens
Takes a lot of time

15. Bibliography http://www.txdps.state.tx.us/CrimeLaboratory/
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