Standardized blood sample preparation is critical for ensuring diagnostic results accuracy. “Garbage in, garbage out” remains a central principle in clinical research, diagnostic development, and laboratory medicine because improper sample handling can lead to specimen degradation that negatively impacts diagnostic reproducibility.

 

Here we summarize the standardized guidelines and best practices for the collection and preparation of blood plasma and serum samples. These recommendations summarize the current guidelines from the Clinical and Laboratory Standards Institute (CLSI) and the Early Detection Research Network (EDRN) standard operating procedures for serum and plasma collection, as well as published specimen collection guidelines from LabCorp and Quest Diagnostics.

 

What is the difference between plasma and serum?

Plasma is the liquid component of whole blood, whereas serum is the liquid component that remains after the blood has clotted. The blood clotting process removes fibrinogen and other components from the sample. Plasma collection requires an anticoagulant to prevent clotting, while serum collection often includes clot activators to allow the sample to fully clot prior to separation.

 

For some diagnostic assays, serum and plasma can be used interchangeably while for others the choice of plasma or serum, and the anticoagulant used, will impact the test results.

 

Use an appropriate plasma or serum collection tube or disc

Whole blood should be collected into an appropriate tube or disc, depending on the desired specimen type (plasma or serum) and assay requirement.

 

Blood for plasma samples should be collected into a tube or disc containing an anticoagulant to prevent blood clotting. The choice of anticoagulant depends primarily on the assay as some anticoagulants can interfere with analytical results. The most common anticoagulants include EDTA, heparin, and sodium citrate.

 

Blood for serum samples, on the other hand, should be collected with clotting activators to help the sample clot prior to the sample separation step. These samples should sit for 30-60 minutes at room temperature to fully clot.

 

Collect the correct blood volume

It is also important to collect the correct volume of blood, as the ratio of blood to additive (anticoagulant or clotting factor) is optimized by the tube or disc manufacturer. Collecting too little blood can cause deleterious effects on the specimen due to an excess of additive, while collecting too much blood can make the additive ineffective.

 

For both plasma and serum, the tube or disc should be inverted 5 to 10 times by hand following collection to adequately mix the specimen with the additive.

 

Centrifuge the sample ASAP

It is important to promptly centrifuge specimens following collection to separate the liquid plasma or serum from the cells and other blood components and preserve the in vivo state of the specimen. Delays in centrifugation can lead to hemolysis and other sources of sample degradation and analytical interference that can impact test accuracy.

Serum and plasma should be separated from cells ASAP graphic
Plasma samples can be spun immediately upon collection, while serum samples can be spun following 30-60 minutes of clotting at room temperature.

 

The severity of delayed centrifugation varies by assay. For example, a maximum delay of 2 hours is recommended for glucose, potassium, lactate dehydrogenase, catecholamines, lactic acid, homocysteine, and molecular RNA assays including HIV-1 and Hepatitis C. Other assays can withstand longer delays, but best practice is to centrifuge and test the specimen as quickly as possible.

 

CLSI guidelines recommend keeping separated plasma or serum samples at room temperature for no longer 8 hours. Separated samples can be kept refrigerated (2 to 8 °C) for up to 48 hours. If samples cannot be tested in this timeframe, the samples should be stored frozen (at or below -20 °C).

 

Sandstone’s Torq System enables new decentralized plasma and serum collection options by bringing the critical centrifugation step to the point of collection so that blood samples can be immediately separated. With Torq, samples are no longer susceptible to hemolysis and other degradation that occurs when conventional centrifuges are not readily available. See our shop for current capillary blood and venous blood collection products available.

 

References

 

  1. Clinical and Laboratory Standards Institute (CLSI).Procedures for the Handling and Processing of Blood Specimens for Common Laboratory Tests; Approved Guideline. Fourth Edition. Wayne, PA, USA: CLSI; 2010. CLSI GP44-A4.
  2. Tuck MK, Chan DW, Chia D, et al. Standard operating procedures for serum and plasma collection: early detection research network consensus statement standard operating procedure integration working group. J Proteome Res. 2009;8(1):113-117. doi:10.1021/pr800545q
  3. Introduction to Specimen Collection. Webpage, accessed Oct 2020. https://www.labcorp.com/resource/introduction-to-specimen-collection
  4. Quest Diagnostics. Serum, plasma, or whole blood collection. Webpage, accessed Oct 2020. https://www.questdiagnostics.com/home/physicians/testing-services/specialists/hospitals-lab-staff/specimen-handling/serum-plasma-whole-blood/

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