Serum and Plasma Specimen-preparations for Clinical Chemistry Testing

After patient identification and preparation, the next vital step towards quality assurance is sample preparation.  It is in this stage that specimens are carefully prepared depending on the substance that will be determined.  Methods differ from one substance to another and these depend upon the intrinsic and extrinsic factors that affect the substance.  Correct sample preparation is one of the factors that ensures reliable laboratory results; hence  the vital  contribution of this step should be reiterated.

In the Clinical Chemistry section, the most  common specimens used  are serum and plasma and sometimes whole blood. Necessary skills to prepare these  blood  specimens should therefore be acquired by the laboratory technologist.

These are the materials needed in the preparation of these blood specimens:

5 test tube, 13 x 100                applicator stick

centrifuge machine                    vial with anticoagulant

pasteur  pipette                        aspirator

test tube rack                            rubber stopper

parafilm                                     evacuated tubes

      A.  SERUM PREPARATION:

1.     Extract  5 ml  of  blood,  or the needed volume, using venipuncture.

2.     Remove the needle and dispense into test tubes. If vacutainer tubes are used, use the red top tube.

3.     Allow to stand at room temperature for 15- 30 minutes. Do not shake.

4.     When the blood has clotted. Rim or ring the specimen by encircling the edges of the test tube with an applicator stick to dislodge clotted blood that hast clung to the tube. We call this process ringing or rimming.

N.B. The indication that the blood has clotted is when it no longer oozes from the tube when it is tilted.

5.     Centrifuge the specimen at 2,500 revolutions per minute (rpm) for 5-10 minutes.

6.     Separate the yellow supernatant fluid, which is your serum,  to another clean and sterile test tube by using a Pasteur pipet. Be certain not to disturb the clot that had settled to the bottom of the tube.

7.     Cover with parafilm and label your sample  completely.

B.    PLASMA PREPARATION:

1.     Extract  5 ml  of  blood, or the needed volume,  using venipuncture.

2.     Remove the needle and dispense into test tubes. Removing the needle would avoid hemolysis.  If vacutainer tubes are used, use specified anticoagulant.

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3.     Mix immediately by gentle inversion to avoid hemolysis. This would also ensure proper sample and anticoagulant mixing.

4.     Centrifuge the specimen at 2,500 revolutions per minute (rpm) for 5-10 minutes.

5.     Separate the yellow supernatant fluid, which is your plasma,  to another clean and sterile test tube by using a Pasteur pipet. Be certain not to disturb the cellular elements that had settled to the bottom of the tube.

6.     Cover with parafilm and label your sample  completely.

Differences of Plasma from Serum