Minimizing Sources of Error with Laboratory Sample Handling and Collection
By Natalie Short, R.V.T., Maple Woods Veterinary Technical Program, Kansas City, Missouri
Your laboratory results are only as good as your sample! Getting accurate results is key in collecting information for a proper diagnosis and creating a specific treatment plan. As technicians, it is our job to make sure that the sample we submit is exceptional quality. Let’s look at the most common sources for error with blood, urine, tissue pathology and fecal samples.
- Make sure patient is fasted to decrease lipemia, which can affect the ability of the machine to properly read chemistry pads. Reduce stress and excitement in animal, as catecholamine release can alter values such as cortisol and glucose.
- Clean stick minimizes platelet activation
- Control aspiration either by not pulling back too hard on the plunger or by choosing a vacutainer system; this will minimize hemolysis which can affect chemistry values.
- Fill tubes appropriately by noting the draw amount on the tube or choose vacutainer that will automatically fill. If the anticoagulant to blood ratio is off it will dilute the sample affecting hematology results.
- Allow proper clot time before spinning; 20-30 minutes
- Spin samples at proper speed; 3500 RPM for 10 minutes to prevent damage of cells.
- Separate serum from red top tube within 1 hour to prevent changes in serum levels.
- Do not use serum separators for hormone or drug analysis testing, such as phenobarbitol, as the gel interferes with levels.
- Ideally a CBC should be done within 2 hours. If that is not feasible, store sample in refrigerator and send to lab with ice packs to prevent high temperatures. At 24 hours, the total WBC and erythrocyte counts should still be viable, but platelet counts may be inaccurate and the differential becomes questionable due to changes in the WBCs. Serum may be frozen if needed.
- Urine samples begin to change very quickly, so they should be run ASAP.
- When collecting, choose method and collector that can minimize trauma. For example, manual expressions are no longer recommended due to the potential for iatrogenic trauma as well as contamination with RBCs. Proper cystocentesis technique can also minimize hemorrhage associated with a traumatic stick.
- Spin at proper speed to minimize cellular damage; 2000 RPMs for 5 minutes.
- As the urine sits, bacteria will begin to grow, pH changes, cells begin to break down and lyse, and glucose values change.
- Refrigeration of sample is preferred if it cannot be read immediately, however that can induce crystal formation
- Samples for parasite identification should be as fresh as possible. An old, dry, crumbly sample will not provide adequate results.
- Ideally the feces should be collected rectally or immediately after evacuation and the middle portion of the sample is best.
- Store in the refrigerator in an airtight container until sample can be read.
- Do not freeze; feces can be prepared with formalin if longer term preservation is needed.
Tissue pathology samples:
- Different tissue samples should be sent in individual jars, with suture tags for orientation if possible.
- Do not store blood smears in the same bags as anything containing formalin.
Proper sample collection, preparation and handling can easily be overlooked. Take a minute to reevaluate your practice’s protocols to make sure samples are yielding the optimal results. Ensure your team is on the same page by creating SOPs that everyone follows to streamline accurate and efficient results.
Natalie Short is one of the two full time RVTs at Maple Woods Veterinary Technology Program in Kansas City, Missouri. She is directly involved in hands-on labs for Clinical Pathology, Small Animal Nursing, Anatomy, Large Animal, Equine and Lab Animal sections. In addition, Natalie oversees the animal care program. For information please contact Natalie at 816-604-3227 or NatalieShort@MCCKC.edu.