Page 2694 - Cote clinical veterinary advisor dogs and cats 4th

von Willebrand Factor Assay 1393

patient’s hydration status, presence or absence pyelonephritis, medullary washout (e.g., Lab Artifacts
of azotemia (i.e., elevated BUN, creatinine), liver dysfunction, hypoadrenocorticism), • USG measurements via dipstick reagent are
VetBooks.ir Reference Interval • Isosthenuria with azotemia is suggestive of • Use of a refractometer with a feline-specific
hypokalemia, and potentially, renal disease
inaccurate.
and urinary and therapeutic history.
calibration scale may result in falsely lowered
renal disease.
• Healthy, euhydrated patient: 1.015-1.045
(dog) and 1.035-1.060 (cat) • Dilute urine/hyposthenuria does not typically USGs in cats. The canine or human scale
indicate renal disease, but can be observed
should be used for feline urine.
• Dehydrated patient with adequate concen- with overhydration, central diabetes insipi-
trating ability: > 1.030 (dog) and > 1.035 dus, and primary polydipsia in addition to Specimen Collection and Handling
(cat) some of the aforementioned causes. Process or refrigerate immediately. Temperature-
• Dehydrated patient with inadequate con- compensated refractometers should be used to
centrating ability: 1.013-1.029 (dog) and Next Diagnostic Steps to Consider measure USG.
1.013-1.034 (cat) if Levels are Low
• Isosthenuria: 1.008-1.012 Exclude drug effects (e.g., diuretic or fluid Relative Cost: $ (reported as part of
• Dilute urine/hyposthenuria: < 1.008 therapy). Assess for glucosuria. Perform com- urinalysis)
plete blood count and biochemistry panel to
Causes of Abnormally High Levels evaluate for azotemia and other abnormalities. Pearls
> 1.030 (dog) and > 1.035 (cat) with azotemia: Evaluate water intake and urinary history. • Dilute urine/hyposthenuria may cause lysis
dehydration Perform abdominal imaging. Consider urine of urinary formed elements (e.g., cells, casts).
culture, leptospira titers, urine cortisol/ • Glucosuria and proteinuria will increase the
Next Diagnostic Steps to Consider creatinine ratio. USG; 1 g/dL of either substance can increase
if Levels are High the USG by ≈0.003 units.
Evaluate hydration status. Important Interspecies Differences
Cats produce more concentrated urine than AUTHOR: Shannon D. Dehghanpir, DVM, MS, DACVP
Causes of Abnormally Low Levels dogs. EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
• < 1.030 (dog) and < 1.035 (cat) in a
dehydrated patient: diuretic/fluid therapy, Drug Effects
osmotic/postobstructive diuresis, hyperad- Fluid, glucocorticoid, or diuretic therapy will
renocorticism, hypercalcemia, pyometra, decrease the USG.

von Willebrand Factor Assay

Definition Reference Interval Lab Artifacts
Diagnostic test for measuring von Willebrand Dogs (quantitative ELISA): 60%-172% of Decrease: hemolysis, clotting Laboratory Tests Laboratory Tests
factor (vWF). Decreased functional vWF causes normal pooled plasma
prolonged bleeding time and abnormal primary Specimen Collection and Handling
hemostasis, known as von Willebrand disease Causes of Abnormally High Levels Collect blood in sodium citrate (blue top tube)
(vWD). Azotemia, liver disease or EDTA (lavender top tube). After centrifu-
gation, plasma should be promptly collected,
Physiology Causes of Abnormally Low Levels frozen, and shipped overnight.
• vWF is produced by endothelial cells and vWD is the most common heritable bleeding
megakaryocytes. It circulates with factor VIII disorder in dogs. Typically, vWF levels < 35% Relative Cost: $$$
(prolongs factor VIII stability). Stored in are indicative of type 1 vWD. Patients with
endothelial cells and platelet alpha-granules, type 2 vWD can have low to normal vWF Pearls
vWF bridges the exposed subendothelial concentrations and variable vWF function. • If the platelet count and coagulation time
collagen and platelets, and among platelets. Concentrations between 30% and 70% suggest are normal and there is no evidence of vas-
Platelet binding of vWF triggers a cascade of a carrier. culitis or platelet dysfunction (e.g., aspirin),
hemostatic and thrombotic events. Low levels prolonged buccal mucosal bleeding time is
of vWF result in lack of platelet activation Next Diagnostic Steps to Consider screening test for vWD.
(p. 1043). if Levels are Low • DNA testing is breed-specific and used
• Type 1 vWD: quantitative vWF deficiency. For several dog breeds, genetic tests can detect to identify potential carriers but does not
Type 2 vWD: quantitative vWF deficiency mutations and identify heterozygotes (i.e., predict the degree to which a dog will be
and concurrent functional deficiencies of carriers). clinically affected. The value obtained from
remaining vWF. Type 3 vWD: no detectable factor assay better predicts the likelihood of
vWF. Important Interspecies Differences clinical signs. DNA test does not help to
• Measured by quantitative ELISA with species- Feline platelets contain vWF; canine platelets diagnose type 3 vWD.
specific antibodies to vWF +/− qualitative do not contain significant levels. Thrombocy- • Breeding should be discouraged for any dog
multimeric analysis (separates the different topenia does not affect vWF values in dogs. with factor levels < 70%.
vWF multimers) to identify type 2 vWD.
Functional assays (platelet aggregation or Drug Effects AUTHOR: Deborah G. Davis, DVM, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
collagen binding assays) are available but Epinephrine, endotoxin, and 1-deamino-8-D-
rarely used in clinical settings. arginine vasopressin (DDAVP) can increase vWF.
www.ExpertConsult.com
www .ExpertConsult.com