Blood Sampling And Packaging Notes

Blood Sampling

1. Plasma versus serum

Plasma is the liquid part of blood that contains red blood cells, white blood cells and nutrients. Plasma is extracted by spinning a blood sample in a centrifuge. Heavier blood cells settle at the bottom and blood plasma is collected from the upper layer using a pipette.

Serum is the fluid part of the blood, without clotting factors or blood cells. Serum is isolated by allowing a blood sample to clot. The liquid is then extracted using an applicator stick and centrifuged to further remove any traces of cells or clot.

The key difference between plasma and serum samples is that plasma contains fibrinogen.

Plasma or serum can be used for most tests, however plasma is not recommended for some analyses.

2. Haematology versus biochemistry

Haematology profile measures the cell components of the blood, such as red blood cell, white blood cell and platelets.

Biochemistry profiles measure chemical substances carried by the blood, such as ions, glucose, enzymes, urea and creatinine.

3. Blood containers

Blood containers are either plain or contain anticoagulant.

Anticoagulant prevents clotting of the blood and is used for plasma and whole blood samples. Anticoagulants include:

• Sodium citrate (blue) – used for determining number of white or red blood cells.

• Heparin (green) – contains lithium or potassium to make chemicals more stable.

• EDTA (purple)

• Sodium fluoride and potassium oxalate (grey) – the fluoride prevents glycolysis, allowing measurement of glucose.

Containers that do not have an anticoagulant are the most commonly used tubes, and are used for serum...

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