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The page below is a sample from the LabCE course Minimizing Pre-Analytical Variability During Venipuncture and Urine Sample Collection Processes. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Time Between Collection and Centrifugation

Following the collection of the sample, there are variables related to the sample handling that may have an effect on result accuracy.
The first to be discussed is the time period between collection and centrifugation. When processing blood for serum, manufacturers of evacuated collection tubes often recommend a period of time to allow the blood to clot prior to centrifugation. This may range from 20-30 minutes depending on the manufacturer. Some manufacturers use a clot activator which is coated onto the interior surface of the tubes. These clot activators serve to reduce the required dwell time to 5-10 minutes. Failure to adhere to these wait periods may result in fibrin clots forming within the serum phase of the centrifuged sample, which may require additional handling to rim the clot and may introduce sample contamination.
On the other extreme, waiting too long between collection and centrifugation provides the environment for ongoing metabolic processes of the viable blood cells within the collection tube. This may result in decreased blood glucose levels and the tendency of components from within the blood cells to leach into the serum. Glucose in whole blood is known to decrease by 7-10% per hour.