what is the shelf life of blood and journey of a blood sample?
by Christa Nuber | 5 min read
Once a blood sample has been collected and labeled, it must be delivered, shipped or otherwise transported to a lab for testing. What is the shelf life of blood samples? Whole blood samples of liquid or “wet” blood have a short shelf life. For example, six weeks is considered the maximum "shelf life" of a blood donation intended for transfusion. After just three weeks, blood is less effective at delivering oxygen-rich cells through the body, and also is less able to flow through the body's smallest capillaries. Here we explore the shelf life of blood and the journey of a blood sample that is collected for lab testing.
Blood Collection for Lab Testing
“For specimen integrity and accurate test results, blood samples must be transported and stored in specific ways,” says James Rudge, PhD, Technical Director, Neoteryx. “The way the blood is initially collected and how it's transported and stored affect its long-term viability.”
For example, a wet blood sample that has been collected via a traditional phlebotomy blood draw into vials or tubes cannot remain at room temperature longer than eight hours.
The Challenges of Keeping Wet Blood Samples Viable
If a wet blood sample is kept at room temperature, in most cases it should be in the laboratory for testing within eight hours of the blood collection event. If testing cannot be completed within that 8-hour timeframe, the sample is typically placed in cold storage at +2°C to +8°C for no longer than seven days. If testing assays are not completed within seven days, or if the sample is to be stored for longer than seven days, it should be frozen at -15°C to -20°C.
The Advantages of Dried Blood Samples
"On the whole, dried blood remains stable at ambient temperatures much longer than wet blood," adds Dr. Rudge. "Dried blood samples usually stay viable for a few weeks at room temperature. Further, many dried blood samples don't require cold shipping or cold storage for medium and sometimes even long-term viability, which is why many research scientists and healthcare professionals have switched to using dried blood samples for their lab testing."
Whether a blood sample is considered “wet” or “dry,” what happens to it once it has been collected?
The Journey of a Blood Sample
Once a blood sample is delivered or shipped to the lab, trained technicians use various methods to analyze it, based on which types of tests are needed. If multiple tests are needed, the lab technicians will use more than one sample of blood. This is why a phlebotomist performing a venipuncture blood draw collects multiple tubes of blood for a single blood test. The phlebotomist knows that if a blood sample is too small, a lab test cannot be repeated to confirm the first result.
Understanding Sample Volume for Lab Testing
A traditional approach to "wet" blood draws is to collect between 2 and 2.5 times the volume that a blood test requires--enough to run two tests of each type. However, most standard blood draws take too much blood, and even after running two tests from a single sample, much of the blood is thrown away.
The same "two times the volume" rule applies to dried blood testing, though a much smaller volume of blood is needed for each test. For example, if you are using a portable device to collect small drops of blood from your fingertip for dried blood testing, you will need to collect the blood drops onto 2-4 device tips or 2-4 spots on filter cards.
Labeling Blood Samples for Proper Identification & Documentation
When blood is being collected, the tubes, devices or filter papers are labeled. This ensures proper matching of blood samples and results to all documents for that individual. In some blood draw centers or labs, the label is pre-printed with the individual's name and their patient identification number. Alternately, the tubes or devices may be labeled with a unique barcode that includes an individual’s pertinent information or a unique string of numbers. If you are self-collecting blood samples at home for dried blood testing, make sure the device or filter paper is labeled with a unique barcode or patient label. It is essential that the tubes, devices or papers are properly labeled before the blood samples leave your side.
At the lab, the label on your blood samples will be logged into a tracking system. This information ensures your samples are tested appropriately and the results are identified with you throughout processing. After testing, the lab will send an electronic form listing your results and other information to the appropriate person, such as your physician or clinical trial manager.
Blood Processing and Testing
For whole blood testing, a blood sample can be analyzed directly with perhaps just a simple dilution. However, depending on which tests are needed, your blood sample is often further processed before it is analyzed. Many blood tests are performed on either plasma or serum, which require a separation step to remove the cellular fraction. Some blood tests, such as neonatal screening for inborn errors of metabolism, are performed from dried blood, which also requires sample processing before analysis.
Plasma, which is the liquid portion of blood, is collected into a tube with anticoagulant. At the lab, plasma is separated from the cellular portion of the wet blood sample by rapidly spinning it in a centrifuge. This centrifugation process pellets the cellular fraction, leaving the straw-colored plasma at the top of the tube.
Serum, which is essentially the liquid left from the clotting process, is obtained by centrifugation where the clotted cellular fragments pellet at the bottom of the tube, leaving the clear liquid at the top of the tube--ready for analysis.
Dried blood is a sample of capillary blood collected from a fingertip or heel-stick that dries on a blood microsampling device or dried blood spot (DBS) card. The tip of the microsampling device or spot on the DBS card that has absorbed the blood is typically added to a tube of liquid for extraction and analysis in the lab. The extractant used will vary according to the type of test. While capillary blood is not identical to venous blood or arterial blood, dried capillary samples deliver results that are equivalent to venous blood samples. They furnish scientific and clinical data that provide both researchers and healthcare providers with critical information.
Blood test results are usually generated electronically as a report that is sent directly to the health practitioner or researcher.
Advances in technology have shortened the time it takes to generate lab results after a blood draw or blood collection event. More complex blood testing may require a few weeks, but in many cases, test results are ready within days after the blood collection event. Once the researcher or healthcare practitioner receives the lab report, they can follow up with the trial participant or patient in the clinic or remotely via telehealth channels: email, phone or video chat. This brings the journey of a blood sample full circle.