A common question often asked of laboratory professionals is the length of time an analyte is stable in a sample. This question may arise simply because a sample has been delayed reaching the lab, but can also be asked in the case of adding on a test to an existing sample a day later, or a week later. Most laboratory professionals can tell you the stability of an analyte in a patient sample, at both ambient temperature and refrigerated, because assay manufacturers perform those short term stability studies when they create their tests. And many of them also include the stability of the analyte in a frozen sample. Beyond this information, it’s harder to find stability information for analytes.
Some stability information can be found at large reference labs, as they have often done their own stability studies and may know how stable an analyte is when frozen for a month, or for 6 months. The really difficult information to come by is how stable an analyte is for really long term storage. This is a question that needs to be answered as biobanking becomes increasingly popular.
Biobanking is the use of repositories to store biological samples, usually for use in later research. Biological material can be stored frozen in many forms, including tissue, cell culture, serum and plasma and dried blood spots. Determining how stable an analyte is under long term storage conditions is important in order to be able to use those samples for research in the future. And yet sometimes determining the long term stability is itself difficult. For example, if a person wished to see if albumin was stable frozen at -80 degrees for 25 years, the difficulty would be in having the same assay available 25 years apart to perform both sets of measurements. (Not to mention the personnel). Measurement technologies change over time, some very rapidly, making longitudinal studies difficult.
The design of studies utilizing biobanked samples will be important. Even when not performing longitudinal studies, if a sample has been stored for 10 years frozen in a biorepository and I remove it and measure the calcium, how do I know the calcium present is the amount of calcium that was present when the sample was stored? If I have knowledge of the patient the sample came from, I could use this data to say that in stored samples, patients with X disease have higher calcium than patients without disease, but I could not necessarily make the jump to what is true in vivo, without knowing how stable calcium is upon long term storage.
Often stored samples are used for measuring analytes that weren’t able to be measured when the samples were originally stored. In those cases, you may be able to infer stability if the amount of analyte measured in the stored samples is comparable to the amount measured in fresh samples.
Biobanking is a growing enterprise, and stability studies will need to grow along with it.
-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.