G

G



Gamma-Glutamyltransferase



DEFINITION


Serum enzyme used as marker for liver disease associated with cholestasis



SYNONYMS


GGT, γ-glutamyltransferase



TYPICAL NORMAL RANGE


Dogs: −0-6 U/L. Cats: −0-4 U/L.



PHYSIOLOGY


Membrane-bound enzyme present in many cells, with biliary epithelium, renal tubular epithelial cells, pancreatic cells, and mammary epithelial cells (especially during lactation) having the greatest activity. Significant increases in serum activity associated primarily with liver disease. Renal urinary GGT may be measured as evidence for renal tubular damage. Colostrum of some species contains high levels of GGT.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Cholestasis, biliary hyperplasia, ingestion of colostrum in neonates; may be induced by corticosteroid administration in dogs



NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH



• Evaluate recent drug administration.

• Measure alkaline phosphatase (ALP), bilirubin, bile acids; liver biopsy.

CAUSES OF ABNORMALLY LOW LEVELS: Low end of reference intervals are usually very low, and low serum levels are not clinically significant.


IMPORTANT INTERSPECIES DIFFERENCES: Colostrum in most species contains high GGT concentrations. Increase in serum GGT occurs within 24 hours of suckling: sensitive indicator of passive transfer. In pups, levels fall to within reference intervals by 10 days of age.



SPECIMEN AND PROCESSING CONSIDERATIONS


DRUG EFFECTS ON LEVELS: Increases secondary to therapeutic drugs causing cholestasis. Increases also seen with anticonvulsant and corticosteroid therapy.


LAB ARTIFACTS THAT MAY INTERFERE: Increase: heparin (therapy or use as anticoagulant for collection) in samples measured by transmission photometry.


SPECIMEN: Serum; separate as soon as possible, store at 8○C.


RELATIVE COST: $ (as individual test); may be included in some chemistry/hepatic chemistry profiles



PEARLS


GGT is more sensitive but less specific than ALP in the cat (for all diseases except hepatic lipidosis) and more specific but less sensitive in the dog.


AUTHOR: LOIS ROTH-JOHNSON


1ST EDITION AUTHOR: FONZIE QUANCE-FITCH



Gastrin



DEFINITION


Group of peptide hormones secreted by G cells of gastric antrum and duodenum in response to protein meal. Functions to stimulate parietal-cell secretion of gastric acid and histamine release by enterochromaffin cells. Also stimulates pancreatic acinar cells when bound to cholecystokinin.



SYNONYM(S)


G-34 (big gastrin), G-17, g-14 (mini gastrin)



TYPICAL NORMAL RANGE


0-27.8 ng/L (most normal dogs have undetectable levels)



PHYSIOLOGY


Ingestion of protein meal stimulates release. Binds to receptors (parietal, enterochromaffin cells), regulating gastric acid release for protein digestion. Enhances digestion by stimulating gastric blood flow, antral motility, and pancreatic secretion. Stimulates DNA, RNA production, and proliferation of parietal cells and gastric mucosa.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Excess secretion (gastrinoma/Zollinger-Ellison syndrome) associated with gastric mucosa hypertrophy, gastric and duodenal ulceration. The underlying cause is typically a neoplasm of pancreatic islet d cells (gastrinoma); when these cells undergo neoplastic transformation, they regain the ability to produce gastrin (normally only occurs in the fetus).


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Evaluate gastric mucosa (endoscopy) for hypertrophy, ulceration; assess for pancreatic islet (8-cell) tumor (abdominal ultrasound and, if a pancreatic mass or liver lesions suggestive of metastases, laparotomy).



SPECIMEN AND PROCESSING CONSIDERATIONS


SPECIMEN: Frozen serum (red-top tube); fasting specimen suggested


RELATIVE COST: $$



PEARLS



• Send out test to specialized gastrointestinal laboratories for most commercial reference labs.

• Recommended cutoff value for diagnosis of gastrinoma is 10 times upper limit of reference interval (278 ng/L).

AUTHOR: LOIS ROTH-JOHNSON



Giardiasis Testing



DEFINITION


Giardia lamblia is a protozoan causing chronic severe diarrhea in pets and humans. Contaminated water is the usual source of infection. Fecal flotation using zinc sulfate detects trophozoites. Fecal ELISA detects antigen. Real-time PCR detects organism DNA.



SYNONYMS


Lamblia intestinalis, “beaver fever”



TYPICAL NORMAL RANGE


Reported as negative or positive for trophozoites (fecal flotation), fecal antigen (ELISA), or DNA (real time PCR).



PHYSIOLOGY



• Zinc sulfate fecal flotation depends on accurate identification of trophozoites in fecal specimens combined with zinc sulfate solution. Trophozoites float to the surface, and an aliquot of fluid is examined microscopically.

• ELISA test detects specific antigens in feces.

• Real-time PCR detects Giardia sp. DNA by amplification of specific genetic material.

• A true positive result with any of these tests indicates shedding, which is likely—but not certain—to indicate causality in a patient with diarrhea.

For example, a prevalence of Giardia infection of up to 40% in puppies has been documented, mostly as subclinical infections.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Intestinal infection


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Identification of organisms or positive detection of antigen or DNA is considered diagnostic of organism shedding, and most clinicians advocate anti-Giardia treatment based on a positive result.


CAUSES OF ABNORMALLY LOW LEVELS: Intermittent shedding, previous antiprotozoal therapy


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: Repeat testing as clinically indicated.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on G

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