Diagnostic Agents-Types and Applications: A Discussion

Introduction

Although biochemistry has long been recognized as a fundamental basis for each of the separate biological and medical sciences, it has now become more and more a common link between biological research and all the medical disciplines, such as physiology, pathology, pharmacology, and so on. Therapy has become increasingly directed towards the correction of pathological conditions by purposeful alteration of biochemical processes. Thus, over the years, a number of substances from the group of biochemicals have been used as Diagnostic Agents beside their use in medicine. The past few decades have been marked by an unprecedented development of diagnostic research. Thus, including the simple diagnostic procedures, enzymes studies, cancer research, vitamin research and others have been helped by the introduction of test reagents.

Diagnosis

Mainly diagnosis is divided in two types :

1. The determination of the nature of a case of disease .

2. The art of distinguishing one disease from another. Further, diagnosis is subdivided into twelve categories depending upon the nature of action taken or work-pattern involve to identify a particular disease. These are :

i. Biological Diagnosis : This is based on tests done on animals.

ii. Clinical Diagnosis : This is based on signs and symptoms of a disease.

iii. Cytohistologic Diagnosis : To detect both benign and malignant by study of exfoliated cells.

.iv. Cytologic Diagnosis : By studying the functions of living cells.

.v. Differential Diagnosis : By comparing clinical findings in two diseases.

vi. Direct Diagnosis : By exclusion process.

vii. Laboratory Diagnosis : By examinations and measurements in laboratory.

viii. Nivean diagnosis : By localization of extent level of a lesion (e.g. tumor).

.ix. Pathologic Diagnosis : By observing structural lesions present.

.x. Physical Diagnosis : By inspection, palpation, percussion and auscultation.

xi. Provocative Diagnosis : By induction of a condition into a diseased body.

xii. Serum Diagnosis : By analysis of serum.

Diagnostic and Diagnostic Agents

 Diagnostic is a process of distinguishing symptoms, and the chemicals which are used to distinguish symptoms are known as diagnostic agents.

Basically, diagnostic agents includes chemical compounds of inorganic or organic nature, most of these being modified in their structural moeity, so as to become specific for their test reactions. These modifications make them biochemicals, depending upon their constitution and functional groups. Inorganic chemicals are not directly functioning as diagnostic agents, but their use, by some way, is essential either to control the reaction process or to provide the necessary conditions for the systematic analysis. Beside the organic reagents used, dyes and stain are an important class of diagnostic agents especially for quantitative determination by colorimetry, which is now the best tool for diagnosis. Radioactive tracers are extensively used in routine clinical diagnosis. Important examples are, studies of the functioning of thyroid gland and to locate the exact site of the tumors of brain by using radioactive iodine, studies of blood circulation time using radioactive sodium and chromium, studies of obscure anaemias and other blood disorders using radioactive iron and studies of important body functions such as digestion, metabolism and excretion. The functioning of different parts and organ systems of the body such as the liver, the kidneys, etc. is also studied by using radioactive isotopes, thus enabling the diagnosis of different disease states. Broadly, we can divide the various compounds used as diagnostic agents into four major classes as :

A. Inorganic and organic compounds used directly.

B. Dyes and stains specifically for use in end point or initial rate colorimetry.

C. Radioactive tracers.

D. Culture-media chemical-basic constituent being Agar. It is worthwhile to discuss some of the compounds which are used either as diagnostic agents or as subsidiary agents to control the conditions and the medium of reactions (pH etc.) and which represent the above classes.

Inorganic and Organic Compounds Used

Ferric ammonium citrate: it is used as bacteriological ingredient.

Sodium chloride: it is used as tissue culture grade.

Bees wax: It is used for histology.

Digitonin: it is used for cholesterol determination.

p-Aminoacetophenone, C8H9ON.

It is a chemical reagent used in a simple method for the chemical determination of urinary thiamine based upon the PrebludaMcCollum reaction.

Bilirubin, C33H36O6N4 Standard in the calorimetric determination of bilirubin in blood, i.e. the estimation of serum bilirubin .

 

This reagent is used in the diagnostic study of the urinary excretion of vitamin B6 by a colorimetric method.

 

 

Used in the diagnosis of vitamin C-sub-nutrition by urine analysis, with a note on the antiscorbutic vlaue of human milk.

Digitonin, C56H92O29

A modified Digitonin used as diagnostic agent for the determination of cholesterol.

x. Buniodyl, 2-[[2,4,6-Triiodo-3-[(1-oxobutyl)amino]phenyl]methylene] butanoic acid monosodium salt , C15H15I3NNaO3.

It gives crystals from water, slightly soluble in water, used as a diagnostic aid in radiopaque medium.

Dyes and Stains

Congo Red: 3,3′-[[Biphenyl]-4,4′-diylbis(azo)-bis [4-amino-1-napthalene sulfonic acid]

It is a brownish-red powder, soluble in H2O and ethanol, insoluble in ether. Used as reagent dye, biological stain as diagnostic aid (amyloidosis)

Acid fuchsin: A widely used plasma stain for connective tissue and stain for bacteriology.
Acridine Orange: A biological stain, fluoroscent dye for cytochemical staining.
Basic fuchsin: Used for staining bacilli, especially influenzae and tubercle, in tissues
Giemsa Stain: Stain used for blood and malarial parasites.
Methyl Green,: A biological stain used as general tissues stain for differentiation of bacteria.
Methylene Blue: A stain for elastic fibres and connective tissue and for tubercle and leprae bacilli in mammalian tissue.
Neutral Red: A general histological and bacteriological stain.
Orange-G: A collagen stain for connective tissue.
Orcein :A histological staining reagent.

Radioactive Tracers ^9,10

Name and Symbol	Form	Use (Diagnostic)
Americium	Encapsulated source	In bone mineral analyzer.
241Am
Chromium	Sodium chromate (Labelled	Study of blood volume and red cell survival,
51Cr	red blood cells)	spleen imaging; placental localization.
Chromium	Labelled human serum	Placental localization; loss of gastrointestinal

 

51Cr	albumin	proteins.
Cobalt	Radioactive Vitamin B12	For absence of intrinsic factor (P.A.) or defect
60Co and 57Co		in absorption (sprue). Metabolic studies.
Copper 64Cu	Copper versenate Copper acetate	Brain scans for tumors, Study Wilson’s disease.
Fluorine 18F	Sodium fluoride (reactor produced)	Bone scan
Gallium	Gallium citrate	Tumor seeking agent
67Ga
Gold	Colloidal gold	Liver imaging
198Au
Indium	Indium-DTPA	Brain imaging
113mIn
Indium	Indium-transferrin	Static cardiovascular blood pool imaging.
113mIn		Hepatic blood pool imaging Placental
		localization
Indium	Indium-Fe(OH)3	Perfusion Lung scan
113mIn
Indium	Indium-colloid	Static liver imaging; spleen imaging
113mIn
Indium	Indium-DTPA	Cisternography
111In
Indium 111In	Indium chloride	Hematopoietic bone marrow imaging; tumour seeking agent
Iodine	Sodium iodide	Thyroid scan. Study action of thyroid and
131I		antithyroid drugs; study of chloride space; aid
		in determining thyroid activity.
Iodine	Diiodofluorescein	Diagnosis and Localization of brain tumors
131I
Iodine 131I	Iodinated serum albumin	Determination of plasma volume, peripheral vascular flow, cardiac output, circulation time
		and cerebral vascular flow. Diagnosis &
		localization of brain tumors. Placental
		localization. Cisternography
Iodine	Macroaggregated iodinated	Perfusion lung scan
131I	serum albumin
Iodine	Colloidal microaggregated	Hepatic blood pool imaging
131I	iodinated serum albumin
Iodine	Iodinated fibrinogen	Determination of fibrinolytic enzymes in vitro
131I
Iodine	Iodinated rose bengal	Liver function in vivo-hepatic excretion studies
131I
Iodine 131I	Iodopyracet, Na Iodo hippurate, Na diatrizoate,	Bilateral renal function test in vivo Kidney imaging
	diatrizoate methyl glucamine,
	Na diprotrizoate, Na
	acetrizoate or Na iothalamate
Iodine	Iodinated fats or fatty acids	Pancreatic function, intestinal fat absorption
131I	e.g. Iodine 131I-triolein
Iodine	Copolymer of p-toluidine	Diagnosis of exudative enteropathy
131I	vinylpyrrolidone 131I
	(Tolpovidone Abbott)
Iodine	Sodium Iodide	Thyroid imaging
125I
Iodine	Iodinated serum albumin	Determination of plasam vol.

 

125I
Iodine	Iodinated rose bengal	Liver function-hepatic excretion studies
125I
Iodine	Iodinated fats	Intestinal fat absorption
125I
Iodine	Sealed source	For use in bone mineral analyzer
125I
Iron	Ferrous citrate FeSO4	Determination of blood vol. with RBC’s
59Fe 55Fe		labelled in vivo, study of iron metabolism;
		blood transfusion studies.
Krypton	Gas	Cardiac abnormalities; skeletal muscle,
85Kr		coronary or cerebral blood flow
Mercury 197Hg 203Hg	Chlormerodin	Brain scans for tumors, renal studies for defects, clearance etc.
Phsophorus	Disodium hydrogen phosphate	Determination of blood vol. with RBC’s labeled
32P		in vitro; study of peripheral vascular disease;
		localization of brain tumors; study of
		carcinomas of breast
Potassium	Potassium carbonate	Localization of brain tumors; determination of
42K		intracellular fluid space
Selenium	Seleno-methionine	Pancreas imaging
75Se
Sodium	Sodium chloride	Study of peripheral vascular disease,
24Na		extracellular space, circulation time, formation
		of cerebrospinal fluid, sodium metabolism.
Strontium 85Sr 87mSR	Strontium nitrate or chloride	Bone imaging in patients with known or suspected malignancies
Technetium	Pertechnetate NaTcO4	Brain scan, Blood pool, placental localization,
99mTc.		thyroid scan
Technetium	Colloidal sulfate	Liver, spleen and bone marrow scans
99mTc.
Technetium	Tc albuminate	Heart scan; placental localization
99mTc.
Technetium	Tc albuminate macro or	Perfusion lung scan
99mTc.	microaggregates
Technetium	Tc DTPA (iron ascorbate)	Kidney scan
99mTc.
Technetium	Tc DTPA (Tin)	Kidney and brain scans
99mTc.
Technetium	Tc stannous polyphosphate,	Bone scan
99mTc.	Tc stannous etidronate
Xenon	Gas or gas in saline solution	Pulmonary function-ventilation studies,
133Xe		Cerebral blood flow; coronary abnormalities;
		skeletal muscle blood flow.
Ytterbium	Yb-DTPA	Cisternography; Brain scan
169
yb

(D) Culture-media chemical-basic constituent being AGAR Agar is a gelatin like material obtained from certain seaweeds; it is chemically related to the carbohydrates. A solution in hot water sets to a firm jelly, which is used as a base for culture media for growing bacteria.

AC Agar : Used for sterility testing

Acetamide Agar : Used for differentiation of nonfermentative gram -ve bacteria, particularly Pseudomonas aeruginosa.

Aeromonas isolation medium base : Used for selective differential isolation of aeromonous hydrophila from clinical specimens.

Anaerobic Agar : Used for isolation and identification of anaerobic pathogens.

Azide Blood Agar Base : Used for selective isolation and cultivation of gram +ve coccistaphylococcus and streptococcus species from clinical and non clinical mixed flora.

Conclusion

 Diagnostic agents are, thus, special chemical compounds which are specific in their reactions by which definite conclusions may be drawn, both qualitative and quantitative regarding the cause of and disease itself. These compounds are helping aids for clinical pathology in general and other branches of medical science. Newer radioactive isotopes, dyes and compounds are proving to be modern diagnostic agents. The more the disease, more the diagnostic agents are to be required.

References

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