Determining the G-ALP portion of ALP has been suggested as a screening test for hyperadrenocorticism but unfortunately many
other conditions are associated with increased G-ALP that is most likely secondary to chronic stress of the disease. Hence,
many question the diagnostic usefulness of G-ALP.
Dogs having increased serum ALP and evidence of vacuolar hepatopathy always should be investigated for hyperadrenocorticism
or glucocorticoid administration. The diagnosis of canine hyperadrenocorticism requires specific testing, such as a low-dose
dexamethasone test or ACTH-stimulation test.
Idiopathic vacuolar hepatopathy
This is a diagnosis frequently observed in older dogs. These cases appear typical of steroid hepatopathies based on histopathologic
examination and abnormal serum ALP, but without clinical or laboratory evidence of hyperadrenocorticism. The liver of these
dogs contains excess glycogen, and they have laboratory findings of predominately G-ALP isoenzymes. One is unable to make
the diagnosis of hyperadrenocorticism based on lack of typical clinical signs and normal conventional adrenal testing (i.e.,
ACTH stimulation or low-dose dexamethasone suppression test). Several dogs recently discovered having vacuolar hepatopathy
and increased serum ALP without overt hyperadrenocorticism have abnormal concentrations in some of the other adrenal steroids
(i.e., sex hormones such as progesterone and 17alpha-hydroxy-progesterone). It has been documented that progestin steroids
bind to hepatic glucocorticoid receptors and will induce a steroid hepatopathy when given orally to dogs. There is now speculation
that increases in progestin steroid hormones may result in the hepatic changes and serum ALP increase. It appears that most,
if not all, of these dogs live a prolonged life without adverse consequences from their liver disease. The reason for abnormal
progestin levels may be secondary to adrenal adenomas, adrenal enzyme deficiency for converting precursors to cortisol or
inapparent adrenal masses. Adrenal adenomas have been shown to secrete high levels of 17-hydroxyprogesterone in dogs.
Recently a disproportionate number of Scottish terriers have elevated serum ALP and hepatic vacuolar changes, suggesting a
breed predisposition for this condition. They may have a genetic defect in ALP production.
Hepatic nodular hyperplasia
Nodular hyperplasia is a benign process causing an increase in serum hepatic values and histomorphologic changes that include
macroscopic or microscopic hepatic nodules containing vacuolated hepatocytes. Liver function remains unchanged. Grossly, the
appearance may be suggestive of chronic hepatitis or neoplasia. The cause is unknown but appears to be an aging change in
dogs; most of those affected are older than 10 years of age. Laboratory findings include a serum ALP increase, but some may
have mild increases in serum ALT and AST concentrations as well. Ultrasound study may be normal or may demonstrate larger
nodules (many can be only microscopic and not observed on ultrasound study). Biopsy confirms the diagnosis; however, a wedge
section is preferred, as a needle biopsy may not demonstrate the nodules. There is no specific therapy.
Dr. Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: