sample collection

chemistry collection

measurements should be completed within 1 hour after blood collection. Freeze sample if testing will be delayed. Freezing will preserve most of the constituents but may affect others. Do not refreeze after thawing.

Preprandial samples

samples from an animal that has not eaten for 12 hours are preferred.

postprandial sample

samples collected after an animal has eaten may produce erroneous results. can produce false values for a number of blood components, including glucose, urea, and lipase.

sample id

date, time of collection, owners name, patients name and patients number.

plasma

fluid portion of whole blood in which the cells are

suspended. It is composed of approximately 90% water and

10% dissolved constituents, such as proteins, carbohydrates,

vitamins, hormones, enzymes, lipids, salts, waste materials,

antibodies, and other ions and molecules. Procedure 19.1 de-

scribes the method for obtaining a plasma sample. The sample

must not be contaminated with any cells from the bottom of the

tube after centrifugation. If the sample cannot be centrifuged

within 1 hour, it must be refrigerated. If heparinized plasma has

been stored overnight after separation or has been frozen, the

sample should be centrifuged again to remove any fibrin strands

that may have formed. Freezing may affect certain test results; the

test instructions should be consulted for all of the tests that must

be run before a plasma sample is frozen.

serum

plasma from which fibrinogen (a plasma protein) has been removed. During the clotting process, the soluble fibrinogen in plasma is converted to an insoluble fibrin clot matrix. When blood clots, the fluid that is squeezed out around the cellular clot is serum. Centrifuging at speeds of more than 2000 to 3000 rpm or for a prolonged time may result in hemolysis. Serum separator tubes (SSTs) contain a gel that forms a physical barrier between serum or plasma and blood cells during centrifugation. The inside walls of the tube also contain silica particles that assist with clot activation. Blood collected into an SST should be mixed by inverting the tube several times and then allowing the sample to clot for 30 minutes before centrifugation. Serum separator transport tubes are also available. These contain approximately double the amount of gel found in a standard SST. The additional gel barrier helps to minimize any interaction between the serum and the cells after centrifugation so that test results are not likely to be affected if tests are delayed. Any prolonged delays in testing require that the serum be removed from the SST and placed in a sterile tube. The tube can then be refrigerated or frozen. Freezing may affect some test results; therefore, the test instructions should be consulted for all tests that must be run before a serum sample is frozen.

hemolysis

may be produced as an artifact when a blood sample is drawn into a moist syringe, mixed too vigorously after sample collection, forced through a needle when being transferred to a tube, or frozen as a whole blood sample. A syringe must be completely dry before it is used, because water in the syringe may cause hemolysis. The needle from a syringe should be removed before blood is transferred to a tube. Forcing blood through a small needle opening may rupture cells. When transferring a blood sample to a tube, the veterinary technician should expel the blood slowly from the syringe without causing bubbles to form. Hemolysis can also result when excess alcohol is used to clean the skin and not allowed to dry before beginning the blood collection procedure. regardless of cause, can greatly alter the makeup of a serum or plasma sample. For example, fluid from ruptured blood cells can dilute the sample, thereby resulting in falsely lower concentrations of constituents than are actually present in the animal. Certain constituents that are normally not found in high concentrations in serum or plasma escape from ruptured blood cells, thus causing falsely elevated concentrations in the sample. Hemolysis may elevate levels of potassium, organic phosphorus, and certain enzymes in the blood. Hemolysis also interferes with lipase activity and bilirubin determinations. Plasma or serum are frequently the preferred sample types over whole blood, and serum is frequently preferred over plasma. can result in release of analytes, release of enzymes, reaction inhibition, increased optical density (absorbance), release of water.

chemical contamination

Sterile tubes are not necessary for the collection of blood samples for routine chemical assays. However, the tubes must be chemically pure. Detergents must be completely rinsed from reusable tubes so that the detergents do not interfere with test results.

improper labeling

Serious errors may result if a tube that contains a sample is not labeled immediately after the sample is collected. The tube should be labeled with

• the date,

• he time of collection, and the

• patient's

• identifying number or name.

The veterinary technician should double check the sample identification with the request form, if one is used, as the sample is prepared and the test is run.

improper sample handling

Ideally, all chemical measurements should be completed within 1 hour of sample collection, but this is not always feasible. In this case, samples must be properly handled and stored so that the levels of their chemical constituents approximate those in the patient's body at the time of collection. Samples must not be allowed to become too warm. Heat may be detrimental to a sample, and it may destroy some chemicals and activate others (enzymes). if a serum or plasma sample has been frozen, it must be thoroughly mixed by gentle inversion after thawing to avoid concentration gradients

patient influences

If practical, a sample should be obtained from a fasting animal (pre-prandial sample)

The blood glucose level can be elevated, and the inorganic phosphorus level decreased, immediately after a meal (postprandial) addition, postprandial lipemia results in turbid plasma or serum. Kidney assays are also affected as a result the transient increase in the glomerular filtration rate after eating. Water intake need not be restricted before obtaining a blood sample.

reference ranges

are also known as normal values. The reference range for a particular blood constituent is a range of values that has been derived when a laboratory has repeatedly assayed samples from a significant number of clinically normal animals of a given species via specific test methods. Therefore, reference ranges may differ depending on the specific test method and analyzer used. Numerous medicine and clinical pathology books list the reference ranges of blood constituents for domestic species. Alternatively, reference ranges may be formulated by local diagnostic laboratories or in individual practice laboratories. Appendix B contains reference ranges for common biochemical constituents. Establishing reference range values for any laboratory is time consuming and expensive. To establish a list of reference values for the laboratory, the veterinary technician would have to assay samples from a significant number of clinically normal animals. Some investigators recommend the analysis of at least 20 animals, and others recommend the analysis of more than 100 animals with similar characteristics. Other considerations include the variety of breeds and species most often seen in the veterinary practice; the gender and reproductive status (e.g., intact, neutered) of the tested animals; and the environment, including husbandry and nutrition, of these animals Climate is also a consideration, because drastic seasonal changes may affect assay results.

lipemia

can cause light scattering, volume displacement, hemolysis

icterus

spectral interference, chemical interaction

hyperproteinemia

can cause hyperviscosity, analyte binding, volume displacement