DIAGNOSTIC-AGENTS

DIAGNOSTIC-AGENTS

Diagnostic agents are used to detect impaired function of the body or to recognize abnormalities in tissue structure. Compounds used in diagnosis are the chemicals employed to determine normal and pathologic products in urine, blood, faeces and other fluids or excrement. There are some other diagnostic agents which are used directly to or in the body. for example radiopaque substances, compounds for testing functional capacity and compounds modifying a physiologic action.

Diagnostic agents are divided into four major groups as follows :

1. Agents used for radiographic purposes

These agents help to reveal anatomic evidence of the disease. They are radiopagues or X-rays contrast media. These are chemicals which cannot be penetrated by X-rays. They absorb radiation and provide a shadow of positive contrast, due to density difference. Barium sulphate, tentalum metal powder spray, metrizoates, diatrizoates, iothalmates, iodomides, iodipamides, iodoxamic acid, iohexol, vocaramate, etc. are used as radiopaques.

Radionucleids are also used for radiographic purposes. They emit radiation and are hazardous agents. Commonly used agents are I' for thyroid function test and thyroid scanning Tc' for blood pool scanning, etc.

2. Agents used for organ function tests

These include drugs used to test liver excretory function (e.g. sulfobromophthalein sodium, phenoltetrachlorophthalein and indocyanine green); to test liver metabolic function (e.g. laevulose), to test capacity for detoxification (e.g. sodium benzoate); to measure glomerular filtration rate (e.g. inuline), to measure renal plasma flow and tubular functional capacity (e.g. aminohippuric acid); to test gastric function (e.g. pentagastrin, betazole HCl); to test pancreatic functions (e.g. secretin, tolbutamide sodium); to test hypothalamic-pituitary function (e.g. metyrapone); to test adrenocortical functions (e.g. corticotrophin, tetracosactrin) and to test thyroid function (e.g. protirelin, thyrotrophin).

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3. Agents used to determine blood volume and hemopoietic functions

Evans blue, indocyanin green and fluorescein sodium are employed to determine blood volume and hemopoietic functions.

4. Agents used for miscellaneous diagnostic tests

Florerscein sodium is applied topically to the cornea to detect minute foreign bodies or corneal ulcers. Amyloidosis is detected by applying Congo red. Benedicts reagent is used as a diagnotic agent for urine analysis. Clinistix, Multistix and Test Tape are reagent strips impregnated with glucose oxidase, peroxidase and orthotolidine. When dipped into urine, blue colour develops on to the strip due to oxidation of orthotoludine. Diastrix is a specific urine glucose test, based on the same principle, which also indicates a rough estimate of the glucose present quantitatively. Ketostrix are the reagent strips used as "dip and read' test for ketone bodies in urine or serum. These contain sodium nitroprusside and other chemical reagents which provide a purple colour if ketone bodies are present. Multistrix are strips containing multiple reagents to detect glucose, ketone bodies and hematuria etc. on a single strip.

There are number of kits available for simple pregnancy test, e.g. Gravidex and Pregnosis. In these tests chorionic gonadotrophins are measured in urine with the aid of specific antibodies.