Page 2657 - Cote clinical veterinary advisor dogs and cats 4th

1360 Lipemia Low-Dose Dexamethasone Suppression Test

Stable at 2°C-8°C for 3 weeks. Avoid than using individual values, continued AUTHOR: Ruanna E. Gossett, DVM, PhD, DACVP
freeze/thaw. increases, decreases, or plateaus of levels EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
VetBooks.ir Relative Cost: $ (serum lipase) • Spec PLI may be measured serially in a
are more meaningful.
confirmed pancreatitis patient (dog or cat)
Pearls
• Degree of increase of lipase in serum does not to assess disease progression.
correlate with severity of pancreatitis. Rather

Lipemia

Definition Next Diagnostic Steps to Consider Pearls
Lipemia is the increased concentration of if Levels Are High • Many laboratories report the presence and
triglyceride-rich lipoproteins (chylomicra • Confirm animal was fasted (12-24 hours) degree of lipemia, as well as the expected
and very-low-density lipoproteins) in blood, before sample collection. If lipemia in dogs severity of interference and analytes affected.
resulting in the cloudy/turbid appearance of persists with fasting, it may be cleared • Analytes that can be artifactually increased
serum or plasma. (to eliminate lipemia-related artifacts) by by lipemia include hemoglobin, MCHC,
injection of 100 U/kg of sodium heparin triglycerides, plasma protein measured by
Physiology intravenously and collection of the blood refractometer, and spectrophotometric assays
Lipemia may interfere with certain laboratory sample 15 minutes later. Triglycerides should for glucose, calcium, phosphorus, alanine
assays by causing dilution of substances in be measured in an aliquot of fasting lipemic aminotransferase (ALT), creatine kinase
serum, or turbidity of the sample, which affects serum before clearing. Ultracentrifugation (CK), and total bilirubin.
the results of spectrophotometric assays. Lipemia may clear lipemic serum to avoid laboratory • Analytes that can be artifactually decreased by
causes hemolysis, which further contributes to interference with other assays. lipemia include lipase, amylase, and albumin.
interference with laboratory assays. Lipemia may • Evaluation for causes of secondary hyper- • Hypercholesterolemia does not cause lipemia.
be normal (i.e., postprandial) or pathologic. lipidemia (p. 1236) is indicated if lipemia
is present in a fasted blood sample. If no AUTHOR: Ruanna E. Gossett, DVM, PhD, DACVP
Reference Interval evidence of these conditions is found, EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
Normally absent from a fasting blood sample consider primary hyperlipidemia.
Causes of Abnormally High Levels
Postprandial specimens, primary or secondary
hyperlipidemias. See pp. 496 and 1236.

Low-Dose Dexamethasone Suppression Test

Definition (ACTH), and subsequent adrenal cortisol are but both > 1 mcg/dL and 8-hour > 4-hour:
The low-dose dexamethasone suppression test suppressed for up to 48 hours. See p. 485. likely PDH
(LDDST) is a screening test for hyperadre- • 4-hour and 8-hour cortisol both < 1.4 mcg/
nocorticism. It sometimes also discriminates Reference Interval dL: normal
between pituitary-dependent hyperadreno- Baseline cortisol: 0.4-6 mcg/dL (dogs); • False increase: icterus, recent adminis-
corticism (PDH) and adrenal tumor (AT) 0.4-4 mcg/dL (cats). Unit conversion: 1 mcg/ tration of glucocorticoid detected by
hyperadrenocorticism (4-hour sample result) dL × 27.6 = 1 nmol/L. Depending on labora- assay
in dogs. tory, suppression is often regarded as < 1.0 to
1.4 mcg/dL. Next Diagnostic Steps to Consider
Physiology if Levels Are High
Patients with hyperadrenocorticism are resis- Causes of Abnormally High Levels • If needed, consider tests to discriminate
tant to negative feedback of cortisol on the Serum cortisol levels: between PDH and AT
hypothalamic-pituitary-adrenal axis, resulting • 4-hour and 8-hour cortisol: failure to sup- ○ Imaging studies
in inadequate suppression of cortisol concentra- press to < 50% of baseline or < 1.4 mcg/ ○ High-dose dexamethasone suppression
tions following administration of dexametha- dL: may be PDH or AT, or technical error test (HDDST) or endogenous ACTH
sone (dogs: 0.01 mg/kg IV; cats: 0.1 mg/kg with injection measurement
IV). Blood is sampled just before, and 4 and 8 • 4-hour cortisol < 1.4 mcg/dL but 8-hour
hours postinjection. In healthy dogs, release of cortisol > 1.4 mcg/dL: consistent with PDH Causes of Abnormally Low Levels
hypothalamic corticotropin-releasing hormone • 4-hour or both 4-hour and 8-hour cortisol(s) If 8-hour suppressed by > 50% below baseline
(CRH), pituitary adrenocorticotropic hormone < 50% of baseline (indicating suppression) (or < 1.4 mcg/dL), hyperadrenocorticism may

www.ExpertConsult.com