Specimen Handling - General Requirements
SERUM, PLASMA OR WHOLE BLOOD COLLECTION
Draw blood in the color-coded Vacutainer® tube indicated in the alphabetical test
listing. For serum or plasma, draw approximately 2 1/2 times the requested volume.
For serum, allow the blood to clot sixty minutes and separate by centrifugation.
For plasma and whole blood, completely fill the Vacutainer whenever possible to
eliminate dilution from the anticoagulant or preservative and immediately mix the
blood by gently and thoroughly inverting the tube five to ten times. Separate plasma
by centrifugation. Transfer the serum, plasma or whole blood to a plastic transport
tube (see Pediatric Specimen Tubes below). To prevent injury and exposure to potentially
infectious material, do not ship frozen serum, plasma, or whole blood received in
glass tubes or SST (glass or plastic).
The color-coded Vacutainer tubes on the inside cover are recommended unless otherwise indicated in the alphabetical test listing. Color-coded pediatric Vacutainer tubes are provided to facilitate special handling.
Most blood specimens can be obtained using routine phlebotomy techniques; however, there are some exceptions. The use of a tourniquet can cause stress and is not recommended in some cases. The patient’s posture either sitting, standing or lying down, or the time of day relative to the patient’s sleep cycle can be important factors in some tests. Whenever specific issues of this nature are important, they will be listed as part of the specimen requirements or patient preparation for the individual tests in the General Test Listing section.
Collect whole blood according to instructions provided for the individual test.
Thoroughly mix the blood with the additives by gently inverting the tube eight times
(four times in the case of light blue-top (sodium citrate) tubes. Maintain the specimen
at room temperature or on cool packs before submitting to our laboratory unless
instructed otherwise by the specimen requirements. Never freeze whole blood unless
specifically instructed in the specimen requirements.
If you store cool packs in the freezer, be sure to allow enough time for them to warm to refrigerator temperature before placing whole blood specimens near them. To minimize the risk of hemolysis, do not place whole blood specimens in direct contact with cool packs.
Plasma contains fibrinogen and other clotting factors when separated from the red blood cells. Evacuated tubes used to collect plasma specimens contain anticoagulant and, frequently, a preservative. The additive in each tube is specified on the label and tube stoppers are color coded according to the additive present. Consult the individual test specimen requirements to determine the correct additive/tube to use. Indicate that the specimen is plasma on the plastic screw-cap vial for transport and test requisition.
Centrifugation: When plasma is required, or when not using a serum gel separator tube, follow these instructions:
- Draw 12 mL of whole blood for each 5 mL of serum or plasma needed. Collect in an appropriate collection tube.
- Centrifuge for at least 15 minutes at 2200-2500 RPM.
- Pipette the serum or plasma into a clean plastic screw-cap vial and attach the label. Do not transfer red cells to the vial. Screw cap on firmly to prevent leakage.
Please check individual specimen requirements for restrictions. When using a serum separator tube, follow these instructions:
- Perform venipuncture as with any other blood collection device.
- Invert the tube gently no more than eight times. Further inversion may cause alterations in sample integrity.
- Do not remove the stopper at any time. Do not centrifuge immediately after drawing blood. Allow the blood to clot in an upright position for at least 30 minutes but not longer than 1 hour before centrifugation.
- Perform venipuncture as with any other blood collection device.
- Centrifuge for at least 15 minutes at 2200-2500 RPM within one hour of collection.
- Transfer the serum to a plastic screw-cap vial for transport to the laboratory.
Note: Do not use serum separator tubes for therapeutic drug monitoring or toxicological analysis. The plastic serum separator material extracts lipophilic substances (most drugs), resulting in a falsely low drug concentration result. Instead, collect the specimen in a plain red-top tube containing no anticoagulants or preservatives. Transfer the serum with a pipette to a plastic vial for transport to the laboratory. Serum should be clear and free from all red cells.
FROZEN SERUM OR PLASMA SPECIMENS
Serum or plasma specimens need to be frozen only if specifically stated in the specimen
requirement. However, in these cases, it is essential to freeze the specimen as
soon as it is separated from the cells. Always freeze specimens in plastic tubes
unless specifically instructed otherwise.
Lay the tube at a 45° angle to avoid tube breakage caused by expansion during freezing. Do not freeze plastic Serum Separator Tubes. An exception is a specimen submitted in a PPT tube; the plasma can be frozen and transported in the original tube.
Extreme cold may cause ordinary plastic labels to become brittle and detach from the specimen tube. Use clear tape to secure label to specimen transport tube.
Note: If more than one test is requested on a frozen specimen, split the sample prior to freezing. Use a separate test requisition when submitting a frozen specimen; frozen and non-frozen specimens must not be submitted on the same test requisition. Indicate on specimen container and test requisition if specimen is plasma or serum.
If more than one test is ordered on a single frozen sample, we will call you to choose which test you want performed before testing can proceed.
COMMON CAUSES OF UNACCEPTABLE SERUM OR PLASMA SPECIMENS AND INACCURATE TEST RESULTS:
Hemolysis occurs when the membrane surrounding red blood cells is disrupted and hemoglobin and other intracellular components escape into the serum or plasma. Hemolyzed serum or plasma varies in color from faint pink to bright red, rather than the normal straw color. Grossly or moderately hemolyzed specimens may be rejected and even slight hemolysis may alter certain test results.
Icteric serum or plasma varies in color from dark to bright yellow, rather than the normal straw color. Icterus may affect certain determinations. Upon receipt of such specimens, we may request a new sample to assure results of diagnostic value.
Turbid, cloudy or milky serum (lipemic serum) may be produced by the presence of
fatty substances (lipids) in the blood. Bacterial contamination may also cause cloudy
serum. Moderately or grossly lipemic specimens may alter certain test results.
A recent meal may produce transient lipemia; therefore, we recommend that patients fast 12-16 hours before a blood specimen is obtained.
Diagnostic procedures or therapy involving radioactive compounds may invalidate radioisotope assays. Obtain specimens for anticipated radioisotope assays before administering isotopes to the patient.