Hematology Red Flags: The Value of Blood Smear Examination in Horses

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Key points

  • •

    Hematologic numerical results provide red flags as to the presence of underlying disease.

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    Examination of a blood smear for morphologic changes, for example, left shift, toxic change, abnormal cells, or infectious agents, is a crucial part of a diagnostic workup; do not rely only on numbers alone.

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    Interpret laboratory data with pertinent clinical information (history, physical examination, and diagnostic imaging).

Blood is our window into the animal. From clinical pathologic results, we can

Case 1

A 21-year-old Quarter Horse mare presented with fever, inappetence, and limb edema. The mare was tachycardic, tachypneic, and febrile, with injected sclera, hyperemic, and tacky mucous membranes, prolonged capillary refill time, and skin tenting. Pertinent results are shown.

Case 1: Hemogram
Test NameResultEmpty CellReference IntervalUnits
Hematocrit (HCT)86(H)34–46%
Red blood cells (RBC)15.8(H)6.6–9.7× 106/μL
Mean cell volume (MCV)5443–55fL
Mean cell hemoglobin concentration (MCHC)3434–37g/dL
White blood cells

Case 2

A 12-year-old Quarter Horse gelding presented with a 3- to 4-day history of colic, fever, and anorexia. The horse had been given penicillin 3 weeks earlier for a leg laceration, which was switched to trimethoprim-sulfonamides. The gelding was quiet, tachycardic, and febrile, with icteric mucosa and the urine was dark red. Pertinent results are shown.

Case 2: Hemogram
Test NameResultEmpty CellReference IntervalUnits
HCT17(L)34–46%
RBC6.5(L)6.6–9.7× 106/μL
MCV5343–55fL
MCHC3734–37g/dL
Red cell distribution width

Case 3

A 15-year-old Hanoverian gelding presented with acute ataxia. Cerebrospinal fluid analysis revealed normal counts and protein, with lymphocytes dominating in a smear. Hemogram results are shown.

Case 3: Hemogram
Test NameResultEmpty CellReference IntervalUnits
HCT33(L)34–46%
MCV4743–55fL
MCHC3534–37g/dL
RDW18.516.3–19.3%
WBC18.0(H)5.2–10.1× 103/μL
Segmented neutrophils9.0(H)2.7–6.6× 103/μL
Band neutrophils0.00× 103/μL
Lymphocytes8.7(H)1.2–4.9× 103/μL
Platelets19094–232× 103/μL
RBC examinationNo significant

Case 4

A 2-year-old Quarter Horse gelding presented with progressive lethargy and decreased performance for 1 month. The horse was tachycardic and tachypneic with pale mucosa. Hematologic results are shown.

Case 4: Hemogram
Test NameResultEmpty CellReference IntervalUnits
HCT10(L)34–46%
MCV59(H)43–55fL
MCHC3634–37g/dL
RDW27.6(H)16.3–19.3%
WBC4.2(L)5.2–10.1× 103/μL
Segmented neutrophils2.2(L)2.7–6.6× 103/μL
Band neutrophils0.00× 103/μL
Lymphocytes1.81.2–4.9× 103/μL
Monocytes0.10–0.6× 103/μL
Platelets29(L)94–232× 103/μL
Mean

Disclosure

The author has no conflicts of interest to disclose.

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