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.
- Sample, when collected, should be subjected to examination.
- Serum and plasma should be separated as soon as possible within 2 hours of collection.
- Don’t try to separate prematurely serum from the blood.
- Give at least 20 to 30 minutes for the clot to form.
- Centrifuge the sample to get a clear serum.
- Premature centrifugation will give rise to the microclots formation and they may create a problem for the automation.
- 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.
- Avoid these samples and possible cause are:
- 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.
- Dark green serum often indicates biliverdin and may be seen in severe obstructive jaundice.
- 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.
- 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.
- If serum shows fine fibrin threads after separation may be due to heparin therapy or other anticoagulant treatment.
- Rarely may see brown tint in the serum and that may be due to the presence of myoglobin following muscle injury or myositis.
- Serum looking more bright yellow may be due to drugs or vitamin supplements.
- Ladies on contraceptive pills may have a green tint in the serum is due to ceruloplasmin.
- The jaundiced serum is yellow and it should be handled with care.
- If the yield of the serum is small, that may indicate hemoconcentration or another possibility is polycythemia.
- The methods and precautions to get a good blood sample are:
- Improve the venepuncture procedure.
- Use plastic beads or gel tubes to get the better serum.
- Plasma if obtained with lithium heparin anticoagulants is a more clear sample.
- Can use serum clarifying filters to get the good serum.
- For glucose use the preservatives which will preserve the glucose and enzymatic methods like lithium iodoacetate.
- Avoid the exposure of the sample to high temperatures.
- Avoid the use of trauma to the sample e.g vigorous handling.
- Don’t keep serum or plasma more than 30 minutes in contact with the cells.
- Potassium level increases 2 to 8 mmol/L without hemolysis and even in the refrigerator.
- If glucose plasma left in contact with cells at room temperature will lose 10% glucose per hour.
- Glucose serum or plasma separated immediately will remain stable for 4 hours in the fridge.
- Serum or plasma for hormones needs even more precautions, best is to freeze the sample.
- Storage of the sample:
- 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.
- If there is a delay in the test then keep serum or plasma at 4 °C.
- If the temperature 4 °C is not suitable for the special test then keep the serum at -20 °C.
- Centrifuge the sample with a stopper which will decrease the evaporation.
- Stopper also avoids the evaporation of volatile analytes like ethanol.
- Stopper also maintained the anaerobic conditions which are needed for CO2 and ionized calcium.
- The use of plastic beads or silicone gel forms a barrier to separate clot from the serum and allow the easy transfer.
- The serum or plasma should not be allowed in contact with cells for more than 30 minutes.
|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|