Siemens ADVIA 1800 Operator's Manual page 84

The use of urine preservatives is beyond the scope of this document. Special analyte-
specific storage conditions such as freezing or protection from direct exposure to light are
noted in the specific clinical method. For example, timely separation of serum from cells is
especially important to prevent elevated results for aspartate minotransferase, lactate
dehydrogenase, magnesium, potassium, and total bilirubin. Erythrocytes normally contain
high concentrations of these analytes, which may increase the serum or plasma
concentration upon standing. Also, glucose test values may decrease upon prolonged
contact with erythrocytes due to the presence of glycolytic enzymes.
In general, separate plasma and serum from cells within two hours of collection. If you
cannot assay samples immediately after separation, store them in stoppered containers at
°
2–8 C.
1. After drawing the specimen from the patient, perform identification procedures
consistent with your laboratory protocol. For serum samples, place the collection
tube in an upright position and allow the specimen to stand undisturbed thirty
minutes to allow clot to form.
2. If you have not used gel separation tubes, carefully separate the clot from the glass
by rimming the collection tube with a wooden stick.
Do not allow the wooden stick to stand (remain) in the tube. Perform this procedure
carefully so the cells are not hemolyzed.
3. If plasma is an acceptable sample type for the particular method, draw the patient
specimen into a tube containing acceptable anticoagulant (lithium heparin or as
indicated in the specific clinical method).
4. Centrifuge the collection tube according to the tube manufacturer's recommendation.
Consult centrifuge manufacturer's instructions for further information on centrifuge
performance.
5. If the clot is attached to the side of the tube and has not dropped to the bottom, repeat
rimming the tube and centrifugation. After centrifugation, examine the primary
collection tubes to ensure that there is a level horizontal separation for serum and
clot. If using a gel tube, you can place the primary collection tube directly into the
sample rack on the system.
6. Alternatively, you can carefully decant the serum from the primary collection tube
into a clean sample cup or secondary tube.
NOTE: Make certain that no clots are decanted into the clean cup or tube. In the case of
plasma, make certain that no fibrin or strands appear in the plasma.
When determining the sample volume requirements for the assays, include the applicable
dead volume:
for collection tubes: 200 μL minimum
for sample cups: 50 μL minimum
IMPORTANT
To avoid having insufficient sample when using sample cups, carefully dispense the
specimen so no air bubbles are entrapped in bottom of the sample cup.
84 ADVIA 1800 Operator's Guide