Collection, processing, and storage of biological samples in epidemiologic studies: sex hormones, carotenoids, inflammatory markers, and proteomics as examples.

The measurement of biomarkers in blood specimens has become an integral component of many epidemiologic studies and introduces several decision points about specimen collection, processing, and storage for the investigator. We briefly discuss the current state of knowledge for four commonly assessed biomarkers: estrogens and other sex hormones, ascorbic acid and carotenoids, cytokines involved in the inflammatory response, and proteomics. Sex hormones are relatively robust to type of sample collected, delayed processing (if chilled), and long-term storage at <-70 degrees C. Ascorbic acid and carotenoids also are relatively robust to sample type and delayed processing (if chilled); however, the blood sample should not be exposed to sunlight and must be stored at <-70 degrees C to prevent substantial degradation. If ascorbic acid is of primary interest, an acid stabilizer should be added during processing. Less is known for cytokines and proteomics, although initial research suggests that these assays are sensitive to varying collection, processing, and storage methods. Overall, we recommend conducting pilot studies if any nonstandard collection, processing, or storage procedure is used. Finally, decisions about these issues depend primarily on the scientific questions of most interest, cost, flexibility, and resources.