Page 2671 - Cote clinical veterinary advisor dogs and cats 4th

Platelets 1373

excretion, ruptured bladder, hypoparathyroid- Next Diagnostic Steps to Consider • Decrease: postprandial carbohydrates (mild),
ism); bone metabolism (e.g., growing animal, if Levels are Low hyperbilirubinemia (with certain assays)
VetBooks.ir Next Diagnostic Steps to Consider profile/urinalysis; ionized calcium Specimen Collection and Handling
osteolytic bone lesions). See p. 1237.
Repeat to rule out artifact. CBC/chemistry
Serum (red top tube) preferred; can also be
if Levels are High
Drug Effects
• Rule out artifact (repeat test). • Decrease: phosphate binding antacids, measured in heparinized plasma (green top
tube) and urine
• CBC/chemistry profile/urinalysis (rule out anesthetics, diuretics, insulin, anticonvul-
urinary, other metabolic disease); consider sants, bicarbonate, mithramycin, salicylates, Relative Cost: $
endocrine testing (PTH levels, thyroid glucocorticoids
hormone [cats]); ionized calcium; survey • Increase: phosphate enemas, intravenous Pearls
skeletal radiographs supplementation, furosemide, vitamin D • Healthy animals < 1 year of age may normally
or vitamin D–containing toxins (p. 164), have serum phosphorus levels that exceed
Causes of Abnormally Low Levels hydrochlorothiazide, minocycline the reference interval for adults.
Misdistribution (e.g., during treatment • Acute hypophosphatemia (e.g., during initial
for diabetic ketoacidosis); increased loss Lab Artifacts management of diabetic ketoacidosis) can
(e.g., Fanconi syndrome in dogs, primary • Increase: hemolysis (in vivo or in vitro), cause severe hemolytic anemia.
hyperparathyroidism); decreased intake (e.g., delayed separation of serum from clot,
hypovitaminosis D, prolonged anorexia). hyperlipidemia, monoclonal gammopathy, AUTHOR: Deborah G. Davis, DVM, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
See p. 1241. thrombocytosis

Platelets

Definition of inflammation (neutrophilia with left shift, • Thrombocytopenia: chemotherapeutic agents,
• Thrombocytopenia: decreased platelet count elevated globulins); +/− serum iron profile; estrogens, phenylbutazone, certain diuretics,
• Thrombocytosis: increased platelet count +/− bone marrow aspirate certain antibiotics/antimicrobials
• Thrombopathia: abnormal platelet function
Causes of Abnormally Low Levels Lab Artifacts
Physiology • Decreased production: FeLV, myelotoxic • Clumping: traumatic venipuncture, clots/
Platelets are discoid, anucleate cytoplasmic drugs, infiltrative bone marrow disease microclots in tube, heparinized sample
fragments, 5-7 mcm in diameter, important (neoplastic, infectious), myelofibrosis • Macroplatelets (decrease due to undercount-
in primary hemostasis. Produced from • Destruction: immune-mediated thrombocy- ing by automated analyzers)
megakaryocytes in bone marrow, spleen, and topenia, infectious disease (e.g., Anaplasma • Severe anemia may cause platelets to appear
lung. They adhere to subendothelium by the platys, babesiosis) increased in blood smears. Laboratory Tests
binding of von Willebrand factor (vWF) to • Consumption: vasculitis (e.g., immune-
platelet glycoprotein Ib (GPIb). Aggregation mediated, Rocky Mountain spotted fever), Specimen Collection and Handling
occurs through binding of platelet membrane disseminated intravascular coagulation, EDTA whole blood (lavender top tube) pre-
a IIb b 3 with fibrinogen or vWF. Activated platelets massive bleeding or thrombosis ferred; citrated whole blood (blue-top tube)
release granule contents (fibrinogen, factor V, • Sequestration (often mild to moderate in can be used.
ADP, ATP, plasminogen), thromboxane A2, and severity): hypersplenism, heartworm disease
arachidonic acid. Mediator release and reactions • Breed related Relative Cost: $ (manual platelet count);
with leukocytes are important in inflammation automated platelet counts and estimates are
and wound healing. Next Diagnostic Steps to Consider reported with CBC ($$)
if Levels are Low
Reference Interval Blood film evaluation to rule out clumping Pearls
• Dogs: 150,000-500,000/mcL and look for hemotropic infectious agents • Breed-related thrombocytopenia does not
• Cats: 150,000-400,000/mcL or macroplatelets; assess history and physical result in bleeding, but breed-related throm-
• 9-15 platelets per 100× field (blood film) exam to identify underlying disorder/trigger; bocytopathia often does result in abnormal
associated with adequate platelet numbers coagulation profile to rule out coagulopathy, bleeding.
DIC; serologic titers or PCR for infectious • Thrombopathia should be considered in
Causes of Abnormally High Levels agents; bone marrow aspirate a bleeding patient with prolonged buccal
Redistribution (exercise, epinephrine release), mucosal bleeding time when platelet
neoplasia (essential thrombocythemia, acute Important Interspecies Differences count, hematocrit, coagulation param-
megakaryocytic leukemia), increased production • Greyhounds have lower platelet counts. eters (prothrombin time, activated partial
(inflammation, iron deficiency, rebound from • β-1 tubulin defect in Cavalier King Charles thromboplastin time), and vWF are normal.
thrombocytopenia), hyperadrenocorticism, spaniels, cairn and Norfolk terriers Document with specific platelet function
immune-mediated hemolytic anemia • Cats: strong propensity for platelet clumping tests.
Next Diagnostic Steps to Consider Drug Effects AUTHOR: Deborah G. Davis, DVM, DACVP
if Levels are High • Thrombocytosis: vincristine, vinblastine, EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
Examine blood film to confirm increase; exogenous corticosteroids
CBC/serum biochemistry profile for evidence

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