Diagnostic Aids & Agents

### Diagnostic Aids & Agents

•  Diagnostic aids are substances used to identify bodily dysfunction. They are not generally used for other medical purposes.
•  The usefulness of these agents depends on:
  • Solubility
  • Excretion rate
  • Metabolism
  • Chemical structure and composition
•  Diagnostic aids are categorized into two main classes: - Clinical diagnostic chemicals: These determine normal and abnormal substances in bodily fluids like urine, blood, and feces.
  • Diagnostic agents: These are applied directly to or within the body.
    • Radiopaque substances: These create shadows on X-rays (e.g., barium sulfate) and are useful in fluoroscopy.
    • Components for testing functional capacity.
    • Compounds that modify physiologic action.

Classification of Diagnostic Agents

• The agents are categorized, based on their function:
  • Gallbladder function (e.g., locetamic acid, lodipamide, tyropanoate sodium)
  • Gastric function (e.g., pentagastrin, Congo red)
  • Liver function (e.g., indocyanine green)
  • Ophthalmic diagnostic aid (e.g., fluorescein sodium)
  • Pancreatic function (e.g., bentiromide)
  • Intestinal function (e.g., Barium sulfate and Xylose)
  • Kidney function (e.g., aminohippurate sodium, indigotin disulfonate, phenolsulphophthalein.)
  • Lymphatic function (e.g., isosulfan blue)
  • Bronchial airway (e.g., methacholine)
  • Hyper-sensitivity (eg. Benzyl penicilloyl polylysine)
  • X-ray contrast medium (e.g., diatriazoic acid, locetamic acid, lothalamic acid, propyliodone)
  • Miscellaneous (e.g., erythrosin sodium, Evans blue)

Radiocontrast Agents

•  These agents are typically iodine or, less commonly, barium sulfate.
•  They enhance the visibility of internal structures in X-ray-based imaging techniques like CT scans and fluoroscopy.
•  They decrease X-ray exposure on detectors.

Intestinal Function—Barium Sulfate

• A water-insoluble, white powder.
• Mixed with water to create a slurry for ingestion or direct administration into the GI tract.
• Used to enhance contrast within the GI tract; it does not dissolve.
• Leaves the body with feces following the examination.

Gallbladder Function—Tyropanoate Sodium

•  An oral radio-opaque agent used in cholecystography.
• Evaluates gallstones and the cystic duct for blockages.
• A radioisotope of iodine.

Locetamic Acid

•  Insoluble in water; soluble in alcohol.
• Used in cholecystography for visualizing the gallbladder.
•  Given as tablets (750 mg each).

Gastric Function—Congo Red

•  A pH-dependent dye; changes color at specific pH values.
• Used to visually assess acid production in the stomach lining.
• Applied as a solution to the stomach lining after pentagastrin stimulation (to ensure enough acid secretion).
• The extent of color change indicates stomach acid secretion ability.

Liver Function—Indocyanine Green

• Dark blue powder used to assess liver function, cardiac output, and liver blood flow.
• Evaluates patients at risk for postoperative liver issues, plasma volume, and blood flow to various organs (kidneys, eyes, lungs).
• A fluorescent dye; detected by light transmission.

Ophthalmic Diagnostic Aids—Fluorescein Sodium

• Orange dye used to detect corneal lesions and foreign objects in the eye.
• Blue light is used to view the dye for improved detection.

Pancreatic Function—Bentiromide

•  Used to assess pancreatic function.
• Contains 4-[(2-benzoylamino)-3-(4-hydroxyphenyl)-1-oxopropyl]amino]benzoic acid.