Specimen Collection, Handling & Chain of Custody

Why Specimen Quality Matters

Every laboratory result depends on the quality of the specimen collected. A poorly collected, mislabeled, or mishandled sample can lead to inaccurate results, delayed diagnosis, and patient harm. As a veterinary assistant or technician, you are responsible for collecting specimens correctly, documenting them completely, and moving them to the right processing station without delay. This lesson covers the four specimen types you will encounter daily: blood, urine (including cystocentesis), fecal, and swab samples.

Blood Collection: Tubes and Technique

Blood is drawn from three common sites in dogs and cats: the cephalic vein (foreleg), the saphenous vein (hindleg), and the jugular vein (neck). Jugular venipuncture yields larger volumes and is preferred for multiple tubes or critical patients. Always use the smallest-gauge needle appropriate for the vessel and the patient's size.

Tube selection sequence is critical. When drawing into multiple tubes from a single venipuncture, the standard order prevents additive carryover that can skew results:

1. EDTA tube (lavender top) — drawn first for complete blood count (CBC). EDTA is an anticoagulant that preserves red and white blood cell morphology.

2. Serum separator tube (SST, gold or red-gray top) — drawn for serum chemistry panels. The gel barrier separates serum from the clot after centrifugation.

3. Red-top plain tube — no additive; used for serology, blood typing, or urine storage when required by the laboratory.

After filling each tube to the manufacturer's fill line, invert it gently the number of times specified for that tube type to mix the additive with blood. Under-filling or over-filling changes the blood-to-additive ratio and invalidates results. Never shake tubes; this causes hemolysis, which falsely alters chemistry values.

Safety: Wear gloves and eye protection for all venipuncture. Cap needles using a one-handed scoop technique or a mechanical recapping device. Dispose of sharps immediately in a puncture-resistant sharps container. Treat all animal blood as potentially zoonotic.

Urine Collection: Cystocentesis

Cystocentesis — aspiration of urine directly from the bladder through the abdominal wall using a needle and syringe — provides the most diagnostically pure urine sample because it bypasses urethral and environmental contamination. It is commonly used for urinalysis and bacterial culture.

On a simulation model, locate the bladder, insert the needle at approximately a 45-degree angle into the bladder lumen, and withdraw urine by gentle negative pressure. Transfer the sample to a labeled red-top tube or sterile urine cup. Record the collection method as "cystocentesis" on the submission form; this information changes how the laboratory interprets bacterial growth on culture. Also record collection time, because urine cellular elements and casts degrade quickly. If analysis is delayed beyond 30 minutes, refrigerate the sample and note the storage temperature.

Other collection methods — free catch (voided) and catheterization — must also be documented, because each method affects result interpretation differently.

Fecal and Swab Specimens

Fecal samples are submitted for parasite identification (direct smear, flotation) or culture. Collect a fresh sample — ideally less than one hour old — using a fecal loop or gloved collection. Place the sample in a labeled fecal cup and note collection time. Refrigerate if processing is delayed. Avoid contamination with litter, soil, or urine.

Swab specimens (ear, skin, wound, nasal, conjunctival) are collected by gently rolling a sterile swab over the target tissue. Use culturette swabs with transport media when the sample will be submitted for culture; the media prevents desiccation and maintains organism viability during transport. Label the swab with the collection site — "left ear canal" is more useful than just "ear."

Labeling: The Non-Negotiable Step

Every specimen must be labeled at the patient's side, before you leave the room, with at minimum:

• Patient name and species
• Client (owner) last name or ID number
• Date and time of collection
• Collection method (e.g., cystocentesis, jugular venipuncture)
• Initials of the collector

An unlabeled tube must be discarded and the patient re-sampled if identification cannot be confirmed with certainty. Never label a tube after the fact from memory.

Chain of Custody and Routing

Chain of custody means that every person who handles a specimen is documented from collection through analysis and disposal. In a clinic setting, this is recorded in the practice-management software or a paper log that captures: who collected it, when, and where it went next.

After labeling and logging, route each specimen correctly:

• EDTA tubes (CBC): immediate analysis or refrigerator (not freezer) if brief delay.
• SST tubes (chemistry): allow to clot (approximately 30 minutes at room temperature), then centrifuge.
• Urine: immediate analysis preferred; refrigerate if delayed.
• Fecal and swabs: process promptly; refrigerate if needed; never freeze swabs in transport media.

Safety Summary

Always wear personal protective equipment (PPE). Treat all biologic specimens as potential biohazards. Dispose of needles in sharps containers immediately after use. Clean and disinfect the work surface after specimen processing. Wash hands before and after handling specimens. Follow your practice's exposure-control plan if a needlestick or splash occurs.