Radioimmunoassays (RIA) are analytical tools for the determination of a wide variety of molecules present in complex matrices. RIA offers high sensitivity by radioactivity measurement, simplicity of the technique, reliability and the requirement for modest equipment and facilities.
The technique introduced in 1960’s for measurement of circulating hormones was later extended to other substances such as tumour markers, viral antigens, drugs, etc. which are useful in clinical management. Other areas, which have benefited from the RIA technique include veterinary science, food industry and drug industry.
RIAs can be performed with commercial IVD certified kits or in-house made sample preparation. Radioimmunoassays (RIAs) use antibodies to detect and quantitate the amount of antigen (analyte) present in a sample.
The immunoassay technique, originally introduced for clinical chemistry applications, is now also used in non-clinical fields including food industry, environmental surveillance, industrial hygiene, drug research, veterinary science and forensic science. The knowledge of levels of various chemicals or other contaminants in food, milk, soil, and water, helps improve quality of livestock and crops, regulate anabolic steroids and monitor toxic compounds in food products.
To perform a radioimmunoassay, a known quantity of an antigen is made radioactive, often by labelling it with gamma-radioactive isotopes of iodine, such as 125-I. The radioactive isotope Iodine-125 is commonly measured with a gamma counter. Hidex AMG equipped with RIA software and standard curve plotting calculations can be used for research purposes to study these concentrations.
Commercial IVD certified RIA/IRMA kits available for measurement include:
Reproductive androgens (Eg. Testosterone)
Thyroid Function (Eg. T3, TSH)
Skeletal (Eg. Vitamin D, PTHrP)
Tumor Markers (Eg. CEA, hCG)
Adrenal Function (Eg. Aldosterone, Cortisol)
Diabetes (Eg. Albumin, Insulin)
Allergy (Eg. Histamin)
Toxic contaminants in environment or food (Eg. Leptin, Atrazine, aflatoxin B1)
Note: details form IAEA-TECDOC-1498 Development of radioimmunometric assays and kits for non-clinical applications
Glomerular Filtration Rate (GFR)
Kidney function assessment is a part of routine medical checkup, essential for assessing overall health, interpreting signs and symptoms, dosing drugs that are excreted by the kidneys, preparing for invasive diagnostic or therapeutic procedures, and detecting, evaluating and monitoring of acute and chronic kidney diseases.
Renal clearance of a substance can occur by two processes: glomerular filtration or tubular secretion. Of these processes, glomerular filtration rate (GFR) is the most representative parameter of renal functionality.
GFR assessment is used for:
Calculation of carboplatin dose in chemotherapy
Assessment of potential living donors for kidney transplantation
Monitoring of patients receiving drugs that can cause nephrotoxicity
Assessment of renal function in patients with chronic kidney disease
Detection of renal failure
Long term urological conditions
Assessment of kidney function as part of work up for receiving a liver transplant
A gamma counter is used to compare the activity of plasma samples taken from the patient with the activity of the standard used as a measure of the injected activity. These results are further calculated to take into consideration age, race, sex and body size.
Hidex AMG, equipped with a 3 inch NaI well type crystal is suitable for accurate activity measurement of common isotopes used in GFR assessment such as Technetium-99m (Tc-99m).
There are no commercial applications available to calculate GFR assessment.
Note: details from BNMS Clinical Guideline for the measurement of glomerular filtration rate (GFR) using plasma sampling 2018
Quality Control of 68 Ge/ 68 Ga Generator
Positron Emission Tomography (PET) imaging agents labelled with 68Gallium (68Ga) have undergone a significant increase in clinical use.
68Ga can be conveniently produced from a commercial germanium-68/gallium-68 (68Ge/68Ga) generator. Because of the compact size and ease of use of the generator, 68Ga labelled compounds may be more cost-effective than PET radioisotopes that are cyclotron-produced.
The favourable half-life of 68Ga (T1/2=68 min) provides ample radioactivity for a range of PET imaging applications while ensuring acceptable radiation doses for patients.
For gallium-68 obtained from a 68Ge/68Ga-generator, the European Pharmacopoeia (Ph. Eur.) includes a dedicated monograph (#2464) outlining specific quality control measures. Due to the contribution or formation of other radionuclides during the production of gallium-68, their amount present in the final radiopharmaceutical must be determined. Different limits for radionuclidic impurities may apply depending on the production method of gallium-68. The testing for these long-lived radionuclides should be carried out after the complete decay of the sample using γ-spectrometry, which represents a post-release batch assessment.
The content of the long-lived parent isotope, 68Ge, in the eluate is assessed to ensure the safety of patients in terms of radiation exposure. The Ph. Eur. monograph sets a limit of 0.001% of Ge68 in the eluate, assuming significant and infinite accumulation of the radionuclide in sensitive organs.
The Hidex AMG software application for Ge68 breakthrough can be used for retrospective analysis of Ga generators. This application, with its protocol and breakthrough limit calculations, offers a user-friendly approach to monitoring and reporting performance results.
Oxygen-15 labelled water
Oxygen-15 labelled water ( [O-15]-H2O) is used as radioactive tracer for measuring and quantifying blood flow using PET (Positron Emission Tomography). Due to its free diffusibility, 15O-water is considered the non-invasive gold standard for quantitative myocardial blood flow (MBF) studies. However, due to Oxygen-15's short half-life of 122 seconds, it has been challenging to provide a radiation safe, controlled, and high-throughput production process. Hidex Radiowater System with the Radiowater Cartridge is an automated production system for Oxygen-15 labelled water.
Hidex instruments find application in various sectors of nuclear medicine, such as performing radioimmunoassays, evaluating Glomerular Filtration Rate (GFR), and conducting quality control assessments on 68Ge/68Ga generators. Additionally, our PET radiochemistry solution, the Hidex Radiowater, facilitates the production of Oxygen-15 labelled water for diagnostics and research.