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Spherocytes 1383

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• Sodium gain: excess ingestion (e.g., seawa- • Intracellular shifting: Na may shift intra- Relative Cost: Individual test, electrolyte
ter, beef jerky, salt-flour dough mixtures), cellularly when severe tissue damage (e.g., panel, or other partial panels: $; included in
VetBooks.ir • See p. 1237. • See p. 1241. Pearls
rhabdomyolysis) or hypokalemia is present
full chemistry panel: $$
hypertonic fluid or sodium bicarbonate
administration, hyperaldosteronism
Next Diagnostic Steps to Consider Next Diagnostic Steps to Consider • Sampling from an improperly cleared intra-
if Levels are Low
venous catheter commonly causes inaccurate
if Levels are High Evaluate hydration status; evaluate for listed values.
Evaluate hydration status; evaluate for listed diseases; measure plasma osmolality. • Most reference laboratory methods are
diseases. subject to electrolyte exclusion effect artifacts.
Drug Effects Portable point-of-care analyzer methods
Causes of Abnormally Low Levels • Increase: osmotic diuretics, furosemide, usually not affected.
• With high measured osmolality: hypergly- phosphate enema, corticosteroids • Hypovolemia causing both hypo- and
cemia, mannitol administration • Decrease: chronic diuretic use hypernatremia may seem paradoxical. Loss of
• With normal measured osmolality: artifactual hypotonic fluid may initially result in volume
(hyperlipidemia, hyperglobulinemia) Lab Artifacts depletion and a relative hypernatremia.
• With low measured osmolality: • Marked hyperlipidemia or hyperglobu- Subsequent water intake and renal water
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○ Hypovolemia: vomiting, diarrhea, peri- linemia may decrease measured Na by conservation may effectively dilute serum
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tonitis, pleural effusion, uroabdomen, electrolyte exclusion effect (if using indirect [Na ].
hypoadrenocorticism, prolonged diuretic potentiometry). • Chronic hypo- or hypernatremia must be
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administration, ketonuria, Na -wasting • Marked hemolysis: may interfere; effect is corrected slowly to prevent brain injury.
nephropathy method dependent
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○ Hypervolemia: heart failure, severe hepa- • Sample handling: Na increases if free water AUTHOR: Mary Leissinger, DVM, MS, DACVP
topathy, nephrotic syndrome, advanced loss from improperly stoppered tube EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
kidney disease (oliguric/anuric)
○ Normovolemia: hypotonic fluid therapy, Specimen Collection and Handling
psychogenic polydipsia, syndrome of inap- Serum (red top tube) preferred. Heparinized
propriate antidiuretic hormone secretion plasma may be used (lithium or ammonium
(SIADH; rare) heparin, green top tube).

Spherocytes

Definition Next Diagnostic Steps to Consider Pearls
Small, dense-staining erythrocytes with no if Levels are High • Microcytic erythrocytes of severe iron- Laboratory Tests
central pallor, considered the hallmark of Evaluate history for causes of anemia; slide deficiency anemia differ from spherocytes
immune-mediated hemolytic anemia (IMHA) autoagglutination test +/- Coombs’ test if in that they are hypochromic and truly
or a normal finding after blood transfusion IMHA suspected microcytic (mean corpuscular volume is
(p. 1327) decreased); spherocytes have normal red
Important Interspecies Differences cell volume and appear hyperchromic.
Physiology Spherocytes are easily detected in dogs because • In anemic patients, a CBC and/or fresh blood
Partial phagocytosis of antibody-coated of normally prominent central pallor; difficult smears to screen for spherocytosis (suggesting
erythrocytes by macrophages causes loss of to identify in cats, which normally have no IMHA) should always be obtained before
surface membrane without loss of volume, central pallor in their erythrocytes. Some breeds transfusion. Spherocytosis after transfusion
resulting in spherocyte formation. Pitting of dogs (shiba inu and Akita) normally have does not discriminate between IMHA and
(excision) of Heinz bodies in the spleen also microcytic erythrocytes that should not be normal post-transfusion phenomenon.
leads to spherocyte formation. May also be seen confused with spherocytes. • Spherocytic anemia or IMHA may not always
in cases of canine babesiosis and hemotropic be accompanied by a positive Coombs’ test
mycoplasmosis in cats and dogs. Specimen Collection and Handling (false-negative result in some cases).
EDTA whole blood (lavender top tube) for • Lack of spherocytes does not rule out IMHA.
Causes of Abnormally High Levels evaluation of gross agglutination and CBC, • Submission of fresh direct blood smear at
Immune-mediated hemolysis, viper and bee fresh blood smear for morphologic evaluation time of blood collection is recommended
sting envenomation, hemoparasitism, zinc to minimize artifacts of morphology due to
toxicosis, neoplasia, or idiopathic; normal phe- Relative Cost: $$ (reported as part of CBC) sample aging.
nomenon beginning 2-3 days after transfusion
of erythrocytes (even if properly cross-matched) AUTHOR: Fidelia R. Fernandez, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP

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