Diagnostic agents are chemicals used to aid in the detection, monitoring, and evaluation of diseases. They do not treat medical conditions but help visualize organs, measure physiological functions, or identify abnormalities in tissues and fluids.
Types of Diagnostic Agents
Diagnostic agents include:
- Contrast media (radiopaque agents)
- Radioisotopes
- Agents used for organ function tests
- Reagents used in biochemical identification
1. Radiopaque Contrast Media
These substances absorb X-rays and appear white on radiographic images, helping outline organs and blood vessels. Most radiopaque media contain iodine or barium because these elements have high atomic numbers and efficiently absorb radiation.
a) Iodinated Contrast Agents
Used for imaging soft tissues such as blood vessels, kidneys, and urinary tract.
Examples
- Iothalamate Sodium
- Diatrizoate Sodium / Meglumine
- Iohexol (non-ionic, low-osmolar)
Uses
- Intravenous pyelography (IVP)
- Angiography
- CT scans
- Hysterosalpingography
Side Effects
- Nausea and vomiting
- Allergic reactions
- Renal impairment (in high-risk patients)
b) Barium Sulphate
Barium sulphate is an insoluble, non-absorbable radiopaque compound.
Uses
- Barium swallow – oesophagus imaging
- Barium meal – stomach and duodenum
- Barium enema – colon imaging
Advantages
- High radiodensity
- Inexpensive
- Non-toxic when used correctly
Contraindications
- Suspected GI perforation (use iodinated agent instead)
2. Radioisotopes
Radioactive substances used for imaging, organ scanning, and functional studies. They emit gamma rays, which are detected by imaging equipment.
Examples
- Technetium-99m (Tc-99m) – most widely used
- Iodine-131 – thyroid imaging
- Cobalt-60 – radiotherapy
Applications
- Bone scans
- Thyroid uptake tests
- Cardiac perfusion imaging
- Renal function imaging
3. Agents Used for Organ Function Tests
a) Liver Function Tests (LFT)
Certain dyes help evaluate hepatic function.
- Bromosulphthalein (BSP) – excretion test for liver function
- Rose Bengal – liver uptake and imaging
b) Kidney Function Tests
- Inulin – gold standard for GFR measurement
- Creatinine – endogenous marker for renal function
- PAH (Para-aminohippuric acid) – renal plasma flow
c) Thyroid Function Tests
- Radioactive Iodine Uptake Test (RAIU)
- Thyroid scanning
4. Agents Used in Ocular Diagnosis
Fluorescein Sodium
A dye used for diagnosing corneal ulcers, abrasions, and foreign bodies.
Features
- Shows bright green fluorescence under blue light
- Useful in tonometry and angiography
Rose Bengal Stain
Used to detect damaged ocular epithelium.
5. Agents for Gastrointestinal Testing
Urea Breath Test Reagents
Used for H. pylori detection.
Lactose Tolerance Test
Checks lactose malabsorption.
6. Agents for Glucose and Metabolic Testing
- Glucose tolerance test (GTT) reagents
- Dextrose solutions for fasting studies
Safety Considerations
While most diagnostic agents are safe, some require precautions:
- Check for iodine allergy before contrast administration
- Ensure proper hydration to protect kidneys
- Radioisotopes should only be used under expert supervision
- Avoid radiological agents during pregnancy unless essential
Detailed Notes:
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