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Lupus Erythematosus Preparation (LE Prep) Luteinizing Hormone (LH) 1361

be absent or atypical, but false-negative result cross-reactive (69%), while dexamethasone best done once nonadrenal illness is resolved
is minimally so (<0.1%).
(if possible) or controlled.
also possible. See p. 487. • Ketoconazole inhibits steroid biosynthesis, • ACTH stimulation testing is generally
VetBooks.ir Next Diagnostic Steps to Consider • Mitotane and trilostane reduce cortisol preferred over LDDST for ruling out
causing low cortisol concentrations.
if Levels Are Low
hyperadrenocorticism in diabetic patients.
If hyperadrenocorticism remains on the differen-
monitor therapy with these drugs.
tial diagnosis, can perform ACTH stimulation production; LDDS is not used as a tool to • ACTH stimulation testing is the only method
to diagnose iatrogenic hyperadrenocorticism.
test or LDDST may be repeated 1-3 months • Very small volumes of dexamethasone are
later. Abdominal imaging can also help by Specimen Collection and Handling used (e.g., 0.01 mg/kg using dexamethasone
defining adrenal size. See pp. 485 and 487. Serum, 1 mL (red top tube); EDTA plasma 4 mg/mL equals 0.01 mL for a 4-kg [9-lb]
(lavender top tube) can be used in some but dog). Therefore, dead space in a regular
Important Interspecies Differences not all test methodologies (e.g., avoid EDTA syringe and needle hub should be consid-
Hyperadrenocorticism is rare in cats. Cats for commonly used Immulite assay). Cortisol ered. Either dilution (add dexamethasone
require administration of 0.1 mg/kg dexa- in EDTA plasma is more stable than in serum. to diluent, not the other way around) or
methasone IV because 15%-20% of healthy Cool specimens are more stable than warm use of an insulin syringe (no dead space in
cats fail to suppress with the 0.01 mg/kg dosage samples. hub) should be considered.
used in dogs. • Dexamethasone-SP must be dosed on the
Relative Cost: $$ to $$$ (depending on basis of the dexamethasone component only
Drug Effects test methodology) (4 mg/mL Dex-SP equivalent to 3 mg/mL
• Long-term use of glucocorticoids leads to dexamethasone).
suppression of cortisol secretion. Pearls
• Immunoassays for cortisol measurement have • Chronic stress and nonadrenal illness can AUTHOR: Carrie Flint, DVM, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
significant cross-reactivity with other gluco- cause false-positive test results; LDDST is
corticoids and drugs. Prednisolone is highly

Lupus Erythematosus Preparation (LE Prep)

Definition Reference Interval Relative Cost: $$
Preparation of incubated clotted blood crushed Reported as negative or positive
through a wire sieve. Blood is collected and Pearls
centrifuged; buffy coat is mixed with equal Causes of Abnormally High Levels • LE cells may occur in skin lesions and joint
amounts of serum, smeared, and stained Positive test indicates active disease (systemic fluid of patients with active SLE.
with Wright stain or new methylene blue. lupus erythematosus [SLE]). • Absence of LE cells does not rule out SLE.
Preparations positive for lupus erythematosus The test is specific for SLE (positive is true Laboratory Tests
(LE) show rosetting of neutrophils around Next Diagnostic Steps to Consider positive) but is a very poor screening test
nuclear material and LE cells (neutrophils with if Levels Are High (low sensitivity; most patients with SLE are
phagocytized homogeneous, magenta-staining Diagnostic evaluation for SLE (p. 955) negative by this test).
nuclear material on a Wright-stained smear). • ANA testing and correlation with clinical
Lab Artifacts signs are needed for diagnosis of SLE.
Physiology Mere phagocytosis of nuclear material with
LE cell formation occurs in the presence of intact chromatin pattern (tart cell) does not AUTHOR: Fidelia R. Fernandez, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
sufficient immunoglobulin G antibody reac- constitute an LE cell.
tive to deoxyribonucleoprotein along with
complement. This antinuclear antibody binds Specimen Collection and Handling
the nuclei of traumatized or nonviable leuko- 5-10 mL of blood in a glass test tube. Hepa-
cytes. Viable neutrophils then phagocytize the rinized blood (green top tube) may also be
opsonized nuclear material, forming the LE cell. used.

Luteinizing Hormone (LH)

Definition and secretion of progesterone. LH is essential Values in intact bitches are low until just before
Glycoprotein gonadotrophin produced by the for corpus luteum formation. In males, LH ovulation. Low concentration is maintained in
anterior pituitary is important for normal growth and function intact cats until ovulation is induced.
of testicular interstitial (Leydig) cells, which
Physiology secrete testosterone. Spayed dogs and cats Reference Interval
In females, LH synergizes with follicle- maintain baseline concentrations since there 2-29 ng/mL; considerable variability during
stimulating hormone (FSH) to initiate ovulation is no inhibition from ovarian estradiol secretion. anestrus

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