Stability of selected serum proteins after long-term storage in the Janus Serum Bank

Background: Human serum from biobanks is frequently used in prospective epidemiological studies. Long-term storage may modify its composition. A better understanding of the stability of the serum components may improve the interpretation of future studies. Methods: The concentrations of selected proteins; immunoglobulins, carrier proteins and enzymes in samples stored at -25 degrees C for 25 years and 2 years were compared with 1-month-old samples. For each length of storage time, 130 specimens were randomly selected from apparently healthy male blood donors aged 40-49 years. We examined the distribution of values, compared dispersion and localization of central tendency, and established reference intervals for each component. Results: The study demonstrated non-significant or numerically small group differences in the concentrations of albumin, aspartate amino transferase, cystatin C, immunoglobulin E, immunoglobulin G, and sex hormone binding globulin. Mean values between fresh and 25-year-old samples suggested larger differences during storage for alanine amino transferase (-73.4%), creatinine kinase (-96.1%), insulin C-peptide (-98.7%), ferritin (-18.5%) and transferrin (+8.2%). Conclusions: The findings showed that long-term storage can introduce a considerable bias for vulnerable components. Clin Chem Lab Med 2009;47:596-603.