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HLT-VET42-09 · Lesson 3 · 26 clock hours · lab

Hematology and Serum Chemistry: In-House Diagnostics

Objective. The student will collect a blood sample using correct venipuncture technique, process it for a complete blood count and basic metabolic panel using in-house analyzer equipment, and interpret results against species reference intervals.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Hematology and Serum Chemistry: In-House Diagnostics

In-house laboratory diagnostics allow the veterinary team to generate critical clinical information within minutes, supporting faster diagnosis and treatment decisions. As a credentialed veterinary technician, you are responsible for the entire diagnostic cycle: collecting the sample correctly, processing it without error, running the analyzers, and interpreting results against species-specific reference intervals.

Pre-Analytical Phase: Venipuncture and Tube Selection

The pre-analytical phase—everything that happens before the sample reaches the analyzer—is the most common source of laboratory error. Errors here cannot be corrected by any analyzer.

Cephalic vein (canine foreleg): Place the patient in sternal recumbency or sitting position. An assistant occludes the vein proximal to the elbow by wrapping a thumb around the lateral foreleg. Insert the needle bevel-up at approximately a 15–30° angle into the raised vein. Release occlusion as you withdraw the needle, and apply gentle pressure with dry gauze.

Jugular vein (feline): The jugular is preferred for cats when a larger sample volume is needed. The cat is restrained in lateral or sternal recumbency with the head extended. The vessel runs from the ramus of the mandible to the thoracic inlet. Use the smallest gauge needle appropriate for the sample volume to reduce patient stress and hemolysis risk.

Tube selection is not interchangeable:

Label every tube at the patient's side, before leaving the room, with patient name, ID, date, time, and your initials. Aseptic technique (clipping and wiping the site with an appropriate antiseptic) protects both the patient and the sample.

Processing: CBC and Chemistry Panel

Complete Blood Count (CBC): The CBC measures red blood cell count (RBC), hemoglobin (Hgb), hematocrit/packed cell volume (HCT/PCV), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), white blood cell count (WBC) with differential, and platelet count. Gently invert the EDTA tube 8–10 times to mix anticoagulant thoroughly before loading the hematology analyzer. Never shake—shaking causes hemolysis and platelet clumping.

Blood smear: Prepare a fresh smear within one hour of collection for best morphology. Place a small drop of well-mixed EDTA blood near one end of a clean slide, use a spreader slide at roughly 30–45° to pull a thin feathered edge, and air-dry immediately. Stain with Wright-Giemsa following the kit protocol. The smear confirms automated differential counts and reveals cell morphology abnormalities the analyzer cannot classify, such as toxic neutrophils, spherocytes, or hemoparasites.

Serum Chemistry Panel: After clotting is complete, centrifuge the SST at the speed and time specified by the tube manufacturer. Remove the serum (the yellow supernatant above the gel barrier) and load it onto the chemistry analyzer cartridge or chemistry rotor. Common analytes include blood urea nitrogen (BUN), creatinine, alanine aminotransferase (ALT), alkaline phosphatase (ALP), total protein, albumin, glucose, and electrolytes.

Centrifuge safety: Balance the centrifuge with tubes of equal weight opposite each other. Never open a running centrifuge. Centrifuge failure during an unbalanced run can cause catastrophic rotor release.

Interpreting Results Against Reference Intervals

Reference intervals represent the range of values found in a healthy reference population of that species. A value outside the reference interval is flagged as high (H) or low (L) but does not by itself establish a diagnosis—it is a finding that must be integrated with the history, physical exam, and other results.

Always use the reference interval printed for the specific analyzer and species you are testing. Canine and feline reference intervals differ substantially for many analytes (e.g., feline ALT and ALP reference ranges are not the same as canine). Confirm the species setting on the analyzer before running.

When you identify abnormal values, ask:

1. Is the abnormality pre-analytical (hemolysis, lipemia, improper tube, improper storage)?

2. Is it consistent with a recognizable pattern (e.g., elevated BUN and creatinine together with low urine specific gravity suggesting azotemia)?

3. What differential diagnoses fit the entire panel, not just one value?

Safety and Scope-of-Practice Reminders

Documenting Findings: The SOAP Note

In the Objective (O) section of the SOAP note, record all laboratory values with units and reference intervals. In the Assessment (A) section, list abnormal findings and at least two differential diagnoses consistent with the panel. The Plan (P) section is completed by or in close collaboration with the supervising veterinarian.

Key terms9

EDTA tubeA blood collection tube containing ethylenediaminetetraacetic acid, an anticoagulant that chelates calcium; required for CBC analysis. Identified by a purple or lavender stopper.
Serum separator tube (SST)A blood collection tube with a clot activator and gel barrier that separates serum from the clot after centrifugation; used for chemistry panels. Identified by a red or gold stopper.
HemolysisThe rupture of red blood cells, releasing hemoglobin into the sample; causes falsely elevated or decreased values for multiple chemistry analytes and renders many results unreliable.
Reference intervalThe statistically derived range of a laboratory value found in a defined healthy population of a given species; values outside this range are flagged as abnormal and require clinical interpretation.
Packed cell volume (PCV) / Hematocrit (HCT)The percentage of whole blood volume occupied by red blood cells; a key indicator of anemia or polycythemia.
AzotemiaAn abnormal elevation of nitrogenous waste products (BUN and creatinine) in the blood, indicating reduced renal filtration; may be pre-renal, renal, or post-renal in origin.
Differential WBC countThe classification of white blood cells by type (neutrophils, lymphocytes, monocytes, eosinophils, basophils) expressed as percentages and absolute counts; used to characterize infection, inflammation, or immune disorders.
Pre-analytical errorAny error that occurs before the sample reaches the analyzer, including improper tube selection, insufficient mixing, hemolysis, mislabeling, or delayed processing; the most common category of laboratory error.
Wright-Giemsa stainA polychromatic stain used on blood smears to differentiate cell types by color; allows visual evaluation of cell morphology, including detection of toxic changes, parasites, and abnormal cells.

Worked examples4

1. A dog's CBC shows a PCV of 28% (reference interval 37–55%). Calculate the percentage by which this value falls below the lower reference limit.
  1. Identify the lower reference limit: 37%.
  2. Subtract the patient value from the lower limit: 37 − 28 = 9 percentage points below the lower limit.
  3. Express the deficit as a percentage of the lower reference limit: (9 ÷ 37) × 100 = 24.3%.
  4. Interpret: The patient's PCV is approximately 24% below the lower reference limit, consistent with moderate anemia.
Answer: The PCV is 9 percentage points (approximately 24%) below the lower reference limit; this finding is consistent with moderate anemia and warrants immediate reporting to the supervising veterinarian.
2. After centrifugation, a serum separator tube yields 2.4 mL of serum. The chemistry analyzer requires 0.5 mL per run. How many replicate runs can be performed from this sample?
  1. Divide total serum volume by volume required per run: 2.4 mL ÷ 0.5 mL = 4.8.
  2. Since a partial run is not possible, round down to the nearest whole number: 4 complete runs.
  3. Note: retain a small aliquot for potential recheck or send-out, so plan for no more than 4 runs in practice.
Answer: 4 complete replicate runs can be performed from the 2.4 mL sample.
3. A feline blood sample is collected into an EDTA tube that should be filled to 1.0 mL but only 0.4 mL of blood was collected. The MCV result reads falsely low. Explain the arithmetic relationship between EDTA volume and blood volume that causes this artifact.
  1. The tube contains a fixed amount of EDTA designed to anticoagulate exactly 1.0 mL of blood (a 1:1 ratio by design of the manufacturer).
  2. With only 0.4 mL of blood, the ratio of EDTA to blood is approximately 2.5 times higher than intended.
  3. Excess EDTA pulls additional water out of red blood cells (osmotic effect), causing them to shrink.
  4. Shrunken cells are measured as having a lower volume, producing a falsely decreased MCV.
  5. Conclusion: underfilling an EDTA tube introduces a systematic pre-analytical error in red cell indices.
Answer: The excess EDTA-to-blood ratio caused osmotic shrinkage of red blood cells, artifactually lowering the MCV. The sample should be recollected in a properly filled tube before results are reported.
4. A canine chemistry panel shows BUN = 58 mg/dL (reference interval approximately 7–25 mg/dL) and creatinine = 3.1 mg/dL (reference interval approximately 0.5–1.5 mg/dL). By how many times do each value exceed the upper reference limit?
  1. BUN: 58 ÷ 25 = 2.32 — BUN is approximately 2.3 times the upper reference limit.
  2. Creatinine: 3.1 ÷ 1.5 = 2.07 — creatinine is approximately 2.1 times the upper reference limit.
  3. Both values are elevated proportionally, supporting azotemia as a true finding rather than a single-analyte artifact.
  4. Report both values with units and reference intervals in the SOAP Objective section and note the pattern to the supervising veterinarian.
Answer: BUN exceeds the upper reference limit by approximately 2.3-fold and creatinine by approximately 2.1-fold; the concurrent elevation of both analytes is consistent with azotemia and must be communicated to the supervising veterinarian promptly.

The math in this lesson1

Learners find a PCV of 28% is 9 points, or 24.3%, below the 37% lower reference limit.
7.RP.3
Brush up in the math halls at newSchoolWorks.com:
In class: Perform venipuncture on a canine foreleg (cephalic vein) and feline jugular (simulated or supervised live) using appropriate restraint, correct tube selection, and aseptic technique, then properly label and process specimens. · Run a CBC and chemistry panel on the collected sample using the in-house hematology and chemistry analyzers; record all numerical values and units on the diagnostic worksheet. · Compare results against printed canine and feline reference intervals, circle abnormal values, hypothesize two differential diagnoses consistent with the panel, and present findings in a structured SOAP note.
Materials: Vacutainer system, EDTA and serum separator tubes, in-house hematology analyzer, in-house chemistry analyzer, centrifuge, microscope, blood smear slides, Wright-Giemsa stain, canine/feline reference interval chart, SOAP note template, Cowell & Tyler's Diagnostic Cytology and Hematology of the Dog and Cat
Check: Instructor-graded diagnostic worksheet and SOAP note: correct technique documented for all pre-analytical steps, all analyzer values recorded accurately, and at least two clinically relevant abnormal values correctly identified and discussed; pass = 85%.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Laboratory Procedures
1. Which blood collection tube is required for a complete blood count (CBC) and why?
Laboratory Procedures
2. A technician collects blood from a cat's jugular vein and notices the sample in the EDTA tube appears pink-red and clear rather than the usual dark red. What pre-analytical error has most likely occurred, and what is the primary concern?
Laboratory Procedures
3. When preparing a blood smear for Wright-Giemsa staining, the technician should make the smear:
Clinical Pathology
4. A dog's serum chemistry shows elevated ALT and ALP with normal BUN and creatinine. Which organ system does this pattern most directly suggest investigating further?
Safety and Infection Control
5. During centrifugation of a serum separator tube, the technician realizes she placed one tube on one side of the centrifuge rotor without a counterbalance tube opposite it. What is the most appropriate action?
Professional Ethics and Legal Issues
6. A canine CBC reveals a WBC of 24,000 cells/µL (reference interval approximately 6,000–17,000 cells/µL) with 90% segmented neutrophils on the differential. Which of the following statements best describes the technician's appropriate role?
Laboratory Procedures
7. Which of the following best describes the purpose of the feathered edge on a properly made blood smear?
Clinical Pathology
8. A feline chemistry panel shows BUN = 65 mg/dL and creatinine = 4.2 mg/dL, both markedly elevated above the reference interval, while the urinalysis specific gravity is 1.012. Which of the following is the most clinically significant interpretation to document and report?
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