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Acetylcholinesterase Level ACTH (Adrenocorticotrophic Hormone), Endogenous 1299

Acetylcholinesterase Level
VetBooks.ir Definition Next Diagnostic Steps to Consider Lab Artifacts

Enzyme that hydrolyzes choline ester neurotrans- if Levels Are High Check with lab for possible artifacts. Anemic
mitters. Measured to confirm organophosphate If organophosphate or carbamate exposure was patients may have lower AChE activity in whole
or carbamate toxicity when clinical signs and suspected but AChE level is within reference blood, owing to lesser amounts of erythrocyte
response to therapy suggest this diagnosis. range, assessment of stomach contents, vomitus, AChE.
or suspected baits for these toxins may be
Synonym(s) helpful. The reversible nature of carbamate Specimen Collection and Handling
Cholinesterase, AChE level binding to AChE can result in higher-than- Heparinized whole blood, 1 mL (green top
expected AChE levels, particularly if the sample tube) or EDTA anticoagulated whole blood
Physiology was handled improperly. (lavender top tube). Check with lab to see
The neurotransmitter acetylcholine (ACh) is which is preferred. Keep sample refrigerated
released from presynaptic cell membranes. AChE Causes of Abnormally Low Levels and ship on ice overnight. Refrigerated serum
at postsynaptic membranes degrades excess ACh Organophosphate or carbamate toxicity; other or frozen brain (caudate nucleus, 5 grams) can
to limit its activity. Organophosphate and carba- toxin exposures are possible, including zinc be submitted from deceased patients.
mate pesticides inhibit AChE activity, leading to phosphide and anatoxin-a(s).
continued cholinergic signaling (depolarization Relative Cost: Whole blood $; blood and
of the cell membrane). Continuous depolariza- Next Diagnostic Steps to Consider brain $$; brain $$
tion may initially be stimulatory, but eventually if Levels Are Low
becomes inhibitory/paralyzing as repolarization Levels <50% of normal are suspicious for AUTHOR: Angela Royal, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
of the membrane is ineffective. organophosphate or carbamate exposure, and
levels <25% of normal are essentially diagnostic.
Reference Interval
Will vary by laboratory. Example: 1895-
5240 U/L (dogs); 736-3016 U/L (cats)

ACTH (Adrenocorticotrophic Hormone), Endogenous

Definition production as an appropriate attempt to increase Drug Effects
ACTH is a pituitary-derived peptide hormone cortisol production. Administration of corticosteroids can suppress
occasionally measured to differentiate pituitary- the hypothalamic-pituitary-adrenal axis, decreas- Laboratory Tests
dependent hyperadrenocorticism (PDH) from Next Diagnostic Steps to Consider ing plasma ACTH concentration.
functional adrenal cortical neoplasia. if Levels Are High
ACTH concentration would be measured only Lab Artifacts
Synonym after confirming a patient has hyperadrenocorti- ACTH is not stable in whole blood, glass tubes,
Corticotropin cism. In these patients, ACTH concentrations or at room temperature or above. Failure to
within or above the reference interval would separate plasma from blood cells promptly or
Physiology confirm PDH. failure to keep the sample frozen or at least
Corticotropin-releasing hormone from the chilled during shipment will result in falsely
hypothalamus triggers release of ACTH from Causes of Abnormally Low Levels decreased ACTH measurement.
the corticotrophs of the anterior pituitary. Hypercortisolemia suppresses the hypothalamic-
ACTH stimulates production of cortisol pituitary-adrenal axis, decreasing ACTH Specimen Collection and Handling
from the adrenal cortex. Normally, cortisol concentration. This may occur in cases of Collect blood into a plastic or siliconized glass
then provides negative feedback to decrease functional adrenal cortical neoplasia causing EDTA tube (lavender top), and immediately
ACTH production. Neoplastic corticotrophs hyperadrenocorticism or with exogenous admin- centrifuge tube to allow for prompt removal of
are not constrained by this regulation. istration of corticosteroids. Rarely, pituitary plasma from blood cells. Transfer plasma to a
Accordingly, in PDH excessive ACTH is pro- trauma, inflammation, or neoplasia can cause plastic tube and freeze. Ship sample overnight,
duced despite the concurrent increased con- inability of corticotrophs to produce adequate and package to ensure that plasma stays frozen
centration of cortisol in blood. See pp. 485 ACTH (secondary hypoadrenocorticism). or at minimum very chilled during transit.
and 487.
Next Diagnostic Steps to Consider Relative Cost: $$
Reference Interval if Levels Are Low
Varies by laboratory. In a patient with hyperadrenocorticism, low Pearls
ACTH concentration suggests functional adrenal Rarely used in clinical practice
Causes of Abnormally High Levels cortical neoplasia. Confirm with abdominal
Pituitary micro- or macroadenomas can produce imaging. AUTHOR: Angela Royal, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
excessive ACTH, causing PDH. Alternatively,
persistent hypocortisolemia in primary hypo- Important Interspecies Differences
adrenocorticism will result in increased ACTH Most commonly measured in dogs.

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