Blood collection tubes must be drawn in a specific order to avoid cross-contamination of additives between tubes.
The recommended order of draw for plastic vacutainer tubes is:
1. blood culture bottle (yellow or yellow-black top)
2. coagulation tube (light blue top).
3. non-additive tube (red top)
additive tubes in this order:
SST (red-gray or gold top) - Contains a gel separator and clot activator.
Sodium heparin (dark green top)
PST (light green top). Contains lithium heparin anticoagulant
EDTA (lavender top)
ACDA or ACDB (pale yellow top)
Oxalate/fluoride (light gray top)
NOTE: Tubes with additives must be thoroughly mixed. Erroneous test results may be obtained when the
blood is not thoroughly mixed with the additive.
Why SERUM is preferred over PLASMA?
1. certain substances like lipemia clearing factor or lipoprotein lipase are co-precipitated during clotting.
2. serum is optically clearer
3. there are potential interference with the use of anticoagulants.
Types of serum:
1. Icteric = yellow colored serum due to increase bilirubin pigment
2. Hemolyze = reddish due to rupture of RBC membrane releasing hemoglobin and other red cell components
3. Lipemic = white colored serum due to high fat content
Serious effects of hemolysis:
1. release of RBC contents including water ↑ K,ACP,Zn,Mg,Na
2. direct interference of hgb. with assays involving color reactions.
transport of specimen
1. Specimen must reach the lab. ideally within 45 mins.
2. During transport agitation must be avoided.
3. prevent direct exposure of the specimen to light especially when planning to measure bilirubin.
4. use dark bottles or cover the specimen receptacle with aluminum foil.
5. transport it in ice especially for unstable substances (ammonia, acid phosphatase, blood gases, catecholamines, plasma renin activity).
Specimen must be stored under suitable conditions:
Ideal temp. for storing serum (long term) is rapid freezing in liquid nitrogen ( -800 C).
For short term storage (6 weeks) -200 C.
prevent clotting of whole blood. They are used when plasma is preferred sample
as in the analysis of acid phosphates whose value is very ↑ when serum is used
because of the disintegration of platelet during clotting.
prevent coagulation by either removing calcium needed in the clotting process or
by neutralizing the enzyme thrombin which converts fibrinogen to insoluble fibrin.
1. Dilution of plasma
2. Inhibition of plasma enzyme activities
3. ↓ calcium levels
4. interference with electrolytes analysis