Laboratory:- Part 4 – Serum, Plasma Preparation, Specimen Storage Precautions

For the preparation of serum or Plasma following precautions or steps are very important to get accurate results.

1. Sample, when collected, should be subjected to examination.
2. Serum and plasma should be separated as soon as possible within 2 hours of collection.
   

   Plasma contents

3. Don’t try to separate prematurely serum from the blood.
4. Give at least 20 to 30  minutes for the clot to form.
   1. Centrifuge the sample to get a clear serum.
   2. Premature centrifugation will give rise to the microclots formation and they may create a problem for the automation.
5. The process of coagulation is complete in 20 to 30 minutes in the glass and silicon tubes but it is delayed in the plastic tube.
   

   Blood sample which should be avoided

6. Avoid these samples and possible cause are:
   1. Dark brown serum indicates intravascular hemolysis with the formation of methemalbumin. This may occur in severe sepsis, hemolytic crises of sickle cell anemia, and paroxysmal nocturnal hemoglobinuria.
   2. Dark green serum often indicates biliverdin and may be seen in severe obstructive jaundice.
   3. If serum was clear and after some time if turbidity appears indicates cryoglobulins, this is usually seen if the serum is kept in the fridge.
   4. If serum is more viscous then check for the paraproteins. In multiple myeloma cases, serum protein may reach 13 g/dL and will produce noticeable changes in the serum.
   5. If serum shows fine fibrin threads after separation may be due to heparin therapy or other anticoagulant treatment.
   6. Rarely may see brown tint in the serum and that may be due to the presence of myoglobin following muscle injury or myositis.
   7. Serum looking more bright yellow may be due to drugs or vitamin supplements.
   8. Ladies on contraceptive pills may have a green tint in the serum is due to ceruloplasmin.
   9. The jaundiced serum is yellow and it should be handled with care.
   10. If the yield of the serum is small, that may indicate hemoconcentration or another possibility is polycythemia.
7. The methods and precautions to get a good blood sample are:
   1. Improve the venepuncture procedure.
   2. Use plastic beads or gel tubes to get the better serum.
   3. Plasma if obtained with lithium heparin anticoagulants is a more clear sample.
   4. Can use serum clarifying filters to get the good serum.
   5. For glucose use the preservatives which will preserve the glucose and enzymatic methods like lithium iodoacetate.
   6. Avoid the exposure of the sample to high temperatures.
   7. Avoid the use of trauma to the sample e.g vigorous handling.
   8. Don’t keep serum or plasma more than 30 minutes in contact with the cells.
   9. Potassium level increases 2 to 8 mmol/L without hemolysis and even in the refrigerator.
   10. If glucose plasma left in contact with cells at room temperature will lose 10% glucose per hour.
       1. Glucose serum or plasma separated immediately will remain stable for 4 hours in the fridge.
   11. Serum or plasma for hormones needs even more precautions, best is to freeze the sample.
8. Storage of the sample:
   1. If there is a delay to centrifuge the sample for any reason then keep the sample at room temp. and don’t refrigerate which may lead to hemolysis.
   2. If there is a delay in the test then keep serum or plasma at 4 °C.
   3. If the temperature 4 °C is not suitable for the special test then keep the serum at -20 °C.
9. Centrifuge the sample with a stopper which will decrease the evaporation.
   1. Stopper also avoids the evaporation of volatile analytes like ethanol.
   2. Stopper also maintained the anaerobic conditions which are needed for CO2 and ionized calcium.

10. The use of plastic beads or silicone gel forms a barrier to separate clot from the serum and allow the easy transfer.
11. The serum or plasma should not be allowed in contact with cells for more than 30 minutes.

	Plasma	Serum
Fibrinogen	0.2 to 0.4 G/dL	Nil
Presence (Site)	Present in the body fluid	Prepared outside the body
Outside the body	Always contains anticoagulant	Never anticoagulant added

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