GENERAL POINTS
Proper Specimen Identification

Identification of specimens is critical if the right result on a given patient is to get back to the right clinician on a timely basis. This includes:

• Writing the animal/client name on each specimen container.
• Writing the animal and client name on the requisition form. The collection date is also helpful.
• Assuring that the originating clinic name and account number is clearly identified on the requisition form.
• Checking that the needed tests are marked or written on the form.
• Indicating the source, if other than a blood sample.
• Identifying the tissue or fluid source and clinic ID # with a lead or wax pencil on all slides submitted for cytology.

Fasting Samples

Fasting the animal for 8-12 hours is often helpful to reduce the likelihood of lipemia, as this may interfere with several tests by falsely increasing or decreasing the results. When applicable, comments about the presence and influence of lipemia appear on the laboratory reports.

• Stabilize serum from serum separator tubes (SST) by centrifuging the specimen before submission. If being mailed, it is preferable to transfer the separated serum to a plain red top tube (RTT).
• Blood samples in plain RTT should be centrifuged and the serum transferred to another RTT.
• Refrigerate and transport all blood specimens, cytology fluids, tissues, viral cultures, and urines for urinalysis (UA! or culture with ice packs. Leave all routine microbial cultures (except urine) and blood cultures at room temperature.
• For specimens that must remain frozen for transport, please obtain your own dry ice.

BLOOD COLLECTION
Tube Sequence

The sequence in which the collected sample is added to the specimen tubes is important to avoid introducing significant variables. Specific concerns include:

• Specimens collected in citrate anticoagulant (blue top tube, BTT> for coagulation testing give the most accurate results with clean venipuncture to minimize contamination with tissue juice. When using the vacuum tube collection system, the SST or RTT is collected first to flush activated clotting factors from the needle. For the direct syringe method, the BTT should be tilled first, unless a blood culture is desired (see Table). All BTT should be collected before the green, gray or lavender tops, as even trace amounts of other anticoagulants can affect the accuracy of coagulation tests.
• As trace amounts of EDTA (lavender top tube, LTT> clinging to a vacuum tube needle can affect the calcium, sodium, potassium and iron levels, fill the RTT or green top tubes beforehand (see Table).
• Trace amounts of sodium fluoride (gray top tube) will affect cell morphology evaluation of the CBC.

The most desirable sequence depends on whether you are using a vacuum tube or syringe assembly for the phlebotomy or are collecting capillary blood from a skin or other puncture site. See Table for a practical guideline.

Hemolysis

The presence of hemolysis of moderate or greater degree can adversely affect the blood specimen in several ways:

• It colors the blood plasma and serum which will interfere with colorimetric chemistry assays.
• It releases intracellular contents, such as proteins and potassium ions, into the serum thereby elevating serum potassium levels of several species and affecting other chemistry values.
• As some red blood cells have been damaged, a falsely depressed Packed Cell Volume (PCV) and Red Cell Count (RBC) will likely be obtained. Although the Hemoglobin value will be accurate, the calculated red blood cell indices will be affected by the depressed PCV and RBC.

Common causes of hemolysis during blood drawing can be minimized with the following suggestions:

1. During phlebotomy, negative pressure created by the vacuum tube or syringe collapses the lumen of the vein against the needle, thereby crushing numerous red cells. The flutter of the lumen against the needle can be stopped by reducing the negative pressure exerted during collection and by repositioning the needle with slight rotation or deeper insertion.
2. Applying excessive negative pressure as the blood enters the vacuum tube or syringe can create hemolysis. This occurs during a slow or difficult collection as the natural tendency is to use more negative force to enhance blood flow. More patience and "milking" the vein by alternating gentle negative pressure with a short release of all pressure usually solves the problem.
3. Hemolysis often occurs during the transfer of blood from a syringe into vacuum or other tubes. If a small gauge needle is used, transfer of blood to specimen tubes is slowed especially if small clots are present. Forcing the blood through a small bore needle contributes further to hemolysis. This problem can be avoided by removing the needle and top of the specimen tube, and transferring the blood directly into the open tube, recapping and aspirating a small amount of air to re-establish negative pressure.

Clots and Platelet Clumps in Anticoagulated Samples

Presence of clots and clumped platelets in anticoagulated blood is most commonly caused by slow blood draw and the resulting delay in mixing it with the appropriate anticoagulant. If the venipuncture was traumatic, tissue juices, activated clotting factors and hemolysis will quickly promote clot formation. The slight transfer delay when using a syringe for collection can also contribute to this problem. The best methods for avoiding clots are:

• Select a vein with good blood flow.
• Minimize the trauma of venipuncture.
• Collect blood directly into anticoagulated vacuum tubes (BTT, LTT).
• Mix the tube well by inverting several times immediately after filling.

If the syringe method is selected and a difficult draw is anticipated, the chance for clotting can be minimized by first rinsing the needle and syringe with a small quantity of liquid citrate (BTT), heparin (green top), or EDTA (LTT). However, the anticoagulant must be emptied from the syringe before proceeding, and care must be taken to match the anticoagulant chosen with the tests to be performed. Even trace amounts of heparin or EDTA will invalidate coagulation testing, whereas EDTA or citrate will alter the accuracy of several chemistry assays. A small amount of heparin contamination is acceptable for most chemistry assays and CBC parameters. Platelet clumping in samples from cats is very common and is caused by contact aggregation. An effective method to prevent this clumping has not been found.

Small Specimen Volumes

Small volumes of blood or other fluids obtained from Avian, Exotic, and Small Mammal species are best collected and transported in Microtainer vessels. The containers are specially constructed to preserve the small specirnen properly and maximize the serum or plasma yield. They are available with all the common anticoagulants used in standard vacuum tubes, including RTT, SST, LTT, and heparin. Microtainers can be filled from a syringe draw, vessel catheterization/drip, or a capillary/skin puncture. However, Microtainers are not vacuum tubes. Please note that capillary hematocrit tubes are not recommended for collection of small specimen volumes.