Cortisol Stability at 16 and 30 Years in Urine Specimens Stored at −20°C

OBJECTIVE: This study aims to investigate whether urinary cortisol can be reliably measured after long-term storage at -20°C, using urine samples collected in 1993 from rural Bangladeshi women, and assayed after 16 and 30 years (2009 and 2023). METHODS: Specimens were collected by participants, placed in coolers with ice packs, transported to a field lab, and then refrigerated for up to 1 week before processing. Specific gravity was measured, and a 6.5 mL sample was archived at -20°C. Urinary cortisol was assayed in 2009 as part of a prior study using enzyme-linked immunosorbent assay (ELISA). In 2023, cortisol was measured in a subsample of 200 specimens using the same assay. RESULTS: = 0.795; p < 0.0001). A paired t-test revealed a bias toward slightly greater values in the 2023 measurements (p < 0.0001). CONCLUSION: These results suggest that urinary cortisol remains largely intact and measurable in specimens stored at -20°C for three decades, and there is a strong correlation between cortisol measured after 16 and 30 years in storage.