Chapter 7 Review: Veterinary Blood Collection and Sample Handling

Practical Principles for Veterinary Blood Collection and Sample Handling

• Core goal: maximize sample quality by using the largest vein and largest needle comfortably tolerated by the animal to minimize cell lysis and obtain more accurate results.
  • General rule: use the largest vein possible with the largest needle comfortable for the patient.
  • Rationale: larger needles reduce shear and lysis of cells during collection.

Vein choices and syringe considerations

• Common small-vessel choices:
  • Lateral saphenous vein
  • Medial saphenous vein
• Syringe size:
  • Typically use a 1 mL syringe when drawing from small vessels.
  • If you switch to a 3 mL syringe and the vessel collapses from negative pressure, switch to a smaller syringe.
  • If you need a larger volume (e.g., 3 mL+), consider using a butterfly catheter or leave the needle attached and spit into a tube, then reattach to avoid multiple punctures.
• For very slow draws or poor venous access, heparin-coated strategies may help (see anticoagulant section).

Fasted sampling and timing

• Some panels (especially GI panels) require fasting; follow your practice protocol.
• Check IDEXX and ANTECH diagnostic panels for fasting requirements and pre-collection fasting duration.
• Always remember: the needle size should be as large as comfortable for the animal to reduce cell damage.

Preferred collection method

• Vacutainer (vacutainer system) is technically preferred in many settings due to:
  • Consistent negative pressure
  • Fewer needle sticks and better cell preservation
  • Reduced risk of introducing air and contamination
• In cats or small volumes (< ~6 mL), a vacutainer may be less practical; consider alternatives (e.g., syringe method) as appropriate.
• Practical note: color-coded tubes contain specific anticoagulants; always verify label and volume requirements.

Needle gauge and catheter sizing

• Needle gauge vs diameter: smaller gauge number = larger diameter.
  • Common shelter range: 25G to 28G; occasionally 18G to 16G in larger or special cases.
  • Equine jugular catheter: typically 12G or 14G and quite long.
• Practical implication: larger gauge reduces hemolysis risk but can be harder to place in small patients; balance with patient comfort.
• When transporting through tubes, minimize the number of times blood travels through a needle to limit lysing and clotting risk.

Equine jugular access and catheter use

• Jugular venipuncture in horses is common but requires hemostasis after puncture.
• For jugular catheters in equines:
  • A catheter kit includes a needle (stylet) and plastic catheter; puncture with the needle, remove the stylet, and place the catheter.
  • Hold pressure for several minutes after placement to ensure hemostasis and reduce hematoma risk.
  • The catheter is typically thick; expect to hold it for a few minutes due to clotting dynamics.

Handling and sample collection etiquette

• Be prepared: have all supplies ready before starting; approach confidently and quickly to minimize animal stress and movement.
• restraint considerations: prolonged restraint increases pain perception and stress; do not restrain longer than necessary.
• if you nick the animal during venipuncture, it increases reactivity; perform clean, decisive punctures.
• after removing the needle, proceed to the collection tube to minimize handling and time the cells spend outside optimal conditions.

Anticoagulants, plasma, and serum basics

• Key definitions:
  • Plasma: blood with anticoagulant preserved, containing clotting factors.
  • Serum: formed after clotting; plasma without clotting factors.
  • Note: clotting factors are found in plasma; once clotting consumes those factors, the resulting serum lacks them.
• When to use anticoagulants:
  • If testing requires whole blood or plasma (e.g., CBCs, certain chemistry panels), use an anticoagulant.
  • If testing is intended on serum, allow the blood to clot and then separate.
• Refrigeration vs freezing:
  • If tests cannot be run immediately, refrigerate samples.
  • Do not freeze blood for most diagnostic tests, as freezing damages cells and skews results.
  • Freezing may be appropriate for transfusion supplies in an emergency, but is not a general practice for diagnostic tests.

Anticoagulants and common tubes (color codes and purposes)

• EDTA (ethylene diamine tetraacetic acid)

  • Color: purple/top depending on brand; EDTA is preferred for CBCs and direct analysis of white blood cells, red blood cells, and morphology.
  • Rationale: preserves cell morphology without altering morphology analyses.
  • Volume considerations: tubes specify how much blood to collect (short tubes ~1 mL; longer tubes ~3 mL).
  • Pitfall: too much EDTA can skew calcium measurements and reduce apparent RBC counts; too little EDTA can cause calcium-rich artifacts and unreliable chemistry results.
  • Order of draw caution: EDTA should be collected last to minimize cross-contamination effects.

• Sodium citrate (blue top)

  • Primary use: coagulation panels and tests requiring intact clotting factors.
  • Ratio caution: too little citrate or too much blood can skew coagulation results; ensure correct blood-to-anticoagulant ratio by filling to the tube’s marked volume.

• Heparin (green top, lithium heparin common)

  • Use: preserve plasma for certain chemistry panels; less interference with certain tests but not universally ideal for all assays.

• Fluoride/oxalate (gray top or sometimes green/blue depending on brand)

  • Sodium fluoride: preserves glucose for glycolysis-sensitive tests; often used when glucose preservation is needed if analysis is delayed.
  • Sodium fluoride-containing oxalate tubes are commonly gray (brand-dependent); always verify with label due to color-code variation.
  • Note: some brands may use green tops for fluoridated/heparin mixtures; verify on tube label.

• Oxalate tubes (less commonly used now)

  • Historically used for glucose preservation and some chemistry tests but less common today.

• Red top (serum)

  • Serum tests after clot formation; lacks clotting factors.

• Practical tube-collection tips:

  • Always fill to at least 3/4 of the tube capacity for EDTA tubes to maintain proper anticoagulant-to-blood ratio and avoid skewed results.
  • Avoid cross-contamination: EDTA drawn first can contaminate other tubes if the needle touches other anticoagulants; in most clinics, EDTA is drawn last to minimize this risk.
  • Label every syringe and tube; unlabeled tubes are discarded to prevent misidentification and errors.
  • Expect variation in color-coding between brands and clinics; always read the label to confirm contents and fill volumes.

• Hypercalcemia diagnostic considerations

  • Two major causes discussed: parathyroid-related disease and anal gland adenocarcinoma (malignancy-associated hypercalcemia).
  • When collecting data, be mindful that improper tube selection or contamination can artifactually influence calcium readings.

Dehydration, PCV interpretation, and anemia considerations

• Dehydration effects on PCV (packed cell volume):

  • Dehydrated animals typically have an elevated PCV; reference dog range is roughly ext{PCV}_{ ext{ref}}

    o 34 ext{ to }55 ext{ extbackslash%}

  • If PCV exceeds the reference range, evaluate for dehydration and clinical signs (see below).

• Clinical signs of dehydration include:

  • Tachycardia? (not explicitly stated, but common)
  • Tacky mucous membranes or dry mucous membranes
  • Skin tenting or reduced skin elasticity
  • Sunken eyes

• Overhydration yields a lower PCV relative to normal range.

• Anemia considerations, especially with kidney disease:

  • Kidney disease can cause anemia due to reduced erythropoietin production.
  • In chronically vomiting dehydrated patients with kidney disease, a normal PCV might mask anemia; consider the clinical context and possible anemia even if PCV appears within reference.

Blood collection technique and post-collection handling

• Supplies should be ready before starting; plan the draw sequence and labeling to minimize errors.
• Confident and efficient technique reduces animal stress and improves sample quality.
• Jugular venipuncture in horses: practical tips include brief compression and quick collection to limit bleeding risk.
• Jugular catheter management in equines:
  • After catheter placement, hold for several minutes to ensure hemostasis.
  • The catheter assembly includes a stylet (needle) and a long plastic catheter; after puncture, remove the stylet and leave the catheter in place.
• Labeling and traceability:
  • Always label tubes; unlabeled syringes/tests will be discarded.
  • Carefully plan the order of draw to minimize cross-contamination between tubes.

Practical exam-style reminders and common pitfalls

• Order of draw (summary):
  • Start with citrate (blue top) when applicable, then other tubes as needed; EDTA should be collected last to avoid interference with chemistry and calcium measurements.
  • In practice, many clinics collect blue top and green top together or red top and purple top together, then complete the set; EDTA is kept last.
• Calibrations and expectations:
  • Be mindful that cross-contamination with EDTA can skew calcium and RBC indices.
  • If a test is sensitive to the anticoagulant used, make sure you have the correct tube type and fill volume.
• Color code awareness:
  • Colors vary by brand and practice; always read the label to confirm contents and fill volumes, not just color.
  • Inconsistent orders or unexpected colors (e.g., 18G appearing where 25G is expected) require double-checking labels and inventory.

Quick reference recap for exam readiness

• Dehydration indicator: PCV > ext{PCV}_{ ext{ref}} ext{ (e.g., }>55 ext{%)} suggests dehydration; assess clinical signs.
• Common anticoagulants and uses:
  • EDTA (purple): CBC and morphology; last in draw order; preserve cellular morphology.
  • Sodium citrate (blue): coagulation panels; plasma required; proper blood-to-anticoagulant ratio.
  • Heparin (green): plasma chemistries; provide quick access to plasma without affecting CBCs.
  • Fluoride/oxalate (gray): glucose preservation when delayed analysis is expected. Color can vary by brand.
  • Oxalate tubes: less common today; check protocol.
• Plasma vs serum: plasma contains clotting factors; serum is plasma minus clotting factors after coagulation.
• Practical tip: have all supplies ready, speak and act confidently, and restrain animals efficiently to minimize stress and movement during collection.

Reflective practice and resources

• Always consult diagnostic panel guidelines (e.g., IDEXX, ANTECH) for fasting requirements and sample handling specifics.
• Review each tube’s fill volume and anticoagulant type on the label before drawing.
• Consider dehydration status and underlying diseases (e.g., kidney disease) when interpreting PCV and related hematology results.

Quick glossary

• PCV: Packed Cell Volume (hematocrit).
• CBC: Complete Blood Count.
• EDTA: Ethylenediaminetetraacetic acid.
• CBC morphology: evaluation of white blood cell and red blood cell shapes and sizes.
• Plasma vs Serum: Plasma contains clotting factors; serum does not.
• Anticoagulant-to-blood ratio: critical for accurate test results; improper ratios can skew results.

End of chapter review: Chapter 7 review questions and practice problems within your transcript materials